Coolant temps too low sticking toward cold!! Help!!?

[mrb5_supra_wrx]

So this really boggles my mind so I got 11 S4 it started having issues with what what I thought was a stuck open thermostat. After replacing said thermostat in less than 3 weeks back to the same issues being.. staying closer toward the cold line or stays on the cold line on colder nights. (Acting like what a stuck open thermostat would ) But weird thing is car will get to temp and stay there at idle but moment you get on the freeway at those speeds with more airflow than a typical street drive coolant temp starts to drop. Sometimes it will do this for a week then go back to acting normal and should hold temps regularly for like couple days, weeks or maybe even a month then goes back to staying to cold. After two thermostat replacement's with brand new thermostats and cts replaced it's blowing my mind . Does anyone one have a clue what else this could be?

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[seandon_792]

Not to be funny but I’d check the thermostat again. The Audi ones just suck, it can be hit or miss. With it being a plastic design it’s prone to failure even after recently being replaced. I have no idea why they only revised the water pump to metal and not revise the thermostat as well.


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[mrb5_supra_wrx]

Not to be funny but I’d check the thermostat again. The Audi ones just suck, it can be hit or miss. With it being a plastic design it’s prone to failure even after recently being replaced. I have no idea why they only revised the water pump to metal and not revise the thermostat as well.


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ive replaced two thermostats and they both did the same thing within the same time frame car drives normal for 2-3 weeks and then back to staying too cold. Im really at a loss for words being i know two thermostats couldnt have just failed sticking open back to back. So its gota be something else. But i have no clue what else could cause it

[CollecTTor]

Im really at a loss for words being i know two thermostats couldnt have just failed sticking open back to back.

Why not? It's a known failure point, and could just be horrible "luck." Absolutely possible though.

[mrb5_supra_wrx]

Why not? It's a known failure point, and could just be horrible "luck." Absolutely possible though.

if thats the case then ecs is to blame being thats where i got both . But theres no reason for two thermostats to both fail open one would have failed closed or something. Yes its a known failure point but something different should have occured by now and then both failing around the same time seems fishy especially when the original thermostat that was in the car when i bought was sticking open as well so technically thats 3 thermostats so how can all three stick open?

[Dr GP]

The T stats in this car usually fail closed. Not saying that can't fail open, but that is more rare. No need for Audi to change t stat design from their prospective. They usually don't fail under 5 yrs or 50k miles. Plus it provides a constant source of revenue for the dealers since it generally fails out of warranty and the process costs more than it should since the SC has to be removed. its always about the money.

[mystik4l06]

if thats the case then ecs is to blame being thats where i got both . But theres no reason for two thermostats to both fail open one would have failed closed or something. Yes its a known failure point but something different should have occured by now and then both failing around the same time seems fishy especially when the original thermostat that was in the car when i bought was sticking open as well so technically thats 3 thermostats so how can all three stick open?

What coolant mix percentage are you using?


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[badazzstang]

if thats the case then ecs is to blame being thats where i got both . But theres no reason for two thermostats to both fail open one would have failed closed or something. Yes its a known failure point but something different should have occured by now and then both failing around the same time seems fishy especially when the original thermostat that was in the car when i bought was sticking open as well so technically thats 3 thermostats so how can all three stick open?

Its not ECS fault but I am sure that they would help correct the problem.

[mrb5_supra_wrx]

What coolant mix percentage are you using?


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50/50 mix g12

[theweebabyseamus]

The T stats in this car usually fail closed. Not saying that can't fail open, but that is more rare. No need for Audi to change t stat design from their prospective. They usually don't fail under 5 yrs or 50k miles. Plus it provides a constant source of revenue for the dealers since it generally fails out of warranty and the process costs more than it should since the SC has to be removed. its always about the money.

I can vouch for him in THIS case, as we’ve been going back and forth with the same issue. My second replacement has been *knocking on wood* performing correctly since then. Mrb5 I forgot to ask on PM, have you done a pressure test of the cooling system?

[mrb5_supra_wrx]

I can vouch for him in THIS case, as we’ve been going back and forth with the same issue. My second replacement has been *knocking on wood* performing correctly since then. Mrb5 I forgot to ask on PM, have you done a pressure test of the cooling system?Haven't pressure tested yea but will when I can get to my buddies shop

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[theweebabyseamus]

I’d be curious to see how it does, mainly because I’m out of ideas.

[mrb5_supra_wrx]

I’d be curious to see how it does, mainly because I’m out of ideas.Another thing to notice if I burp the system by letting it sit and idle get to Temp and then relieve pressure by taking the reservoir cap off it seems to act fine for a few days or however long and then it goes back to staying cold. Could this be from air getting in the system somehow? Would that was it Maybe? And I don't know I'm out of ideas as well

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[xtim8719x]

Another thing to notice if I burp the system by letting it sit and idle get to Temp and then relieve pressure by taking the reservoir cap off it seems to act fine for a few days or however long and then it goes back to staying cold. Could this be from air getting in the system somehow? Would that was it Maybe? And I don't know I'm out of ideas as well

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Maybe the thermostat is fine and your temp sensor is failing?

If you have the old thermostats that you removed available, test them to see if they operate correctly. Put them in a pot of water on the stove and see if they open/close at the correct temp. If they work correctly, look elsewhere.



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[xtim8719x]

Maybe the thermostat is fine and your temp sensor is failing?

If you have the old thermostats that you removed available, test them to see if they operate correctly. Put them in a pot of water on the stove and see if they open/close at the correct temp. If they work correctly, look elsewhere.



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Sorry I missed in your initial post that you replaced the cts already. But I would till test the old thermostats if you have them.


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[mrb5_supra_wrx]

Maybe the thermostat is fine and your temp sensor is failing?

If you have the old thermostats that you removed available, test them to see if they operate correctly. Put them in a pot of water on the stove and see if they open/close at the correct temp. If they work correctly, look elsewhere.



Sent from my iPhone using Audizine (http://r.tapatalk.com/byo?rid=87676)Temp sensor was replaced 6 months ago and temp sensor wouldn't make the heat not operate to proper temp as well when it's staying cold

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[theweebabyseamus]

Another thing to notice if I burp the system by letting it sit and idle get to Temp and then relieve pressure by taking the reservoir cap off it seems to act fine for a few days or however long and then it goes back to staying cold. Could this be from air getting in the system somehow? Would that was it Maybe? And I don't know I'm out of ideas as well

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That's the direction I was heading. I cant say how it would affect the car to make it run cold, maybe just forcing the t-stat open more? The cap is supposed to relieve pressure when it gets to a certain point, maybe you have air getting in the system and the cap isn't releasing it.

Edit: I would test the old t-stats as well.

[mrb5_supra_wrx]

That's the direction I was heading. I cant say how it would affect the car to make it run cold, maybe just forcing the t-stat open more? The cap is supposed to relieve pressure when it gets to a certain point, maybe you have air getting in the system and the cap isn't releasing it.

Edit: I would test the old t-stats as well.

starting to wonder could a bad pcv/crankcase breather cause this? Being coolant flows through the the valve?

[Dr GP]

What would happen if you drove without the cap for 20-30 miles?

[mrb5_supra_wrx]

What would happen if you drove without the cap for 20-30 miles?

havent tested this yet why do say that?

[Dr GP]

havent tested this yet why do say that?

Might be helpful to remove any trapped air if there actually is some.

[S4'ed]

starting to wonder could a bad pcv/crankcase breather cause this? Being coolant flows through the the valve?

The pass thru coolant passage, through the PCV unit, can't have anything to do with your too-cool issue.....it is just a pipe....

I replaced my thermostat a few weeks ago, and I recall that there is a hole, at the bottom of the opening in the aluminum engine block (where the thermostat sits in), that the metal rod, at the center of the thermostat has to fit into. Maybe the new thermostat is not being installed straight down into the opening, and therefore the metal rod is not mating into the hole. Maybe that cocks the thermostat seal off its base, which then allows coolant to flow when it shouldn't. Was it difficult to seat the thermostat into the opening? It is not easy to install it straight down, as you have to also engage the connection of the cross over pipe too. Did you loosen and/or remove the screws that hold the crossover pipe to the left and right cylinder head? (this allows the crossover pipe to be moved forward, so you can engage the center slip-joint into the thermostat).

[mrb5_supra_wrx]

Anyone have thoughts on if leaking intercoolers could also cause cooling temps to be too cold? I know I have minor misfire at idle which I know is prob not plugs and just had a carbon cleaning done. Thoughts?

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[CollecTTor]

Anyone have thoughts on if leaking intercoolers could also cause cooling temps to be too cold?

No. But are you losing coolant over time?

[mrb5_supra_wrx]

No. But are you losing coolant over time?

yea i am actually. Trying to figure this out so any random lil thing that could possibly maybe be it trying to rule it out

[CollecTTor]

yea i am actually. Trying to figure this out so any random lil thing that could possibly maybe be it trying to rule it out

Sounds like your IC is leaking into the cylinders, but that wouldn't have any affect on operating temps.

[S4'ed]

So...what do you think of post #22...I bet that is your issue. Who did the thermostat replacement work ? You?

[theweebabyseamus]

So...what do you think of post #22...I bet that is your issue. Who did the thermostat replacement work ? You?

It would have to go into that channel or the t-stat wouldn't sit down far enough to secure the bolts.

[mrb5_supra_wrx]

Sounds like your IC is leaking into the cylinders, but that wouldn't have any affect on operating temps.
Well im kinda wondering that some have mentioned before that maybe could be from air in the system or no enough flow. But was wondering the air getting into the coolers from them leaking and also cooling the system down too much . But idk still at a loss for words been this is the third thermostat and still have the same issues. Only other thing i could think of it being is my lack of flow / restriction in the plumbing or heater core or something. Weird thing is on warmer days its fine most of the time but here during the winter now its been doin it and staying cold. Also burping the system allows it to function properly for a while then it goes back to sticking cold eventually. I dont understand it never seen something like this before.



So...what do you think of post #22...I bet that is your issue. Who did the thermostat replacement work ? You?
I had the work done at a local indie shop. And i pretty sure its what weebabyseamus said about it not being able to be secured and sealed if not properly level or in the spot but i havent dont the thermo myself but from what ive seen i thought that was the case as well

[CollecTTor]

Well im kinda wondering that some have mentioned before that maybe could be from air in the system or no enough flow. But was wondering the air getting into the coolers from them leaking and also cooling the system down too much . But idk still at a loss for words been this is the third thermostat and still have the same issues. Only other thing i could think of it being is my lack of flow / restriction in the plumbing or heater core or something. Weird thing is on warmer days its fine most of the time but here during the winter now its been doin it and staying cold. Also burping the system allows it to function properly for a while then it goes back to sticking cold eventually. I dont understand it never seen something like this before.




I didn't even think about it because I've only seen it mentioned that the IC's leak into the cylinders. Boost would push coolant into the charge path but vacuum would pull air from the charge path into the cooling system. That may be why you burp/purge/bleed the system, and it acts normal until enough air gets into the system to cause the cooling issue.

[mrb5_supra_wrx]

I didn't even think about it because I've only seen it mentioned that the IC's leak into the cylinders. Boost would push coolant into the charge path but vacuum would pull air from the charge path into the cooling system. That may be why you burp/purge/bleed the system, and it acts normal until enough air gets into the system to cause the cooling issue.Yea I was kinda starting to wonder if something like this was possible.. idk tho

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[S4'ed]

The opposite : boost would force air into the cooling system. and vacuum will pull water into the cylinders. But I can't think of a reason that air pockets in the cooling system will cause the engine to run too cool, usually an air pocket causes an overheat condition, as the pocket can impede coolant flow.

The only reason the engine can run too cool is that the thermostat is allowing coolant flow to the radiator when it shouldn't. It is either not closing properly, or it is opening at too low of a temperature.

[mrb5_supra_wrx]

The opposite : boost would force air into the cooling system. and vacuum will pull water into the cylinders. But I can't think of a reason that air pockets in the cooling system will cause the engine to run too cool, usually an air pocket causes an overheat condition, as the pocket can impede coolant flow.

The only reason the engine can run too cool is that the thermostat is allowing coolant flow to the radiator when it shouldn't. It is either not closing properly, or it is opening at too low of a temperature.

well ive had three different thermostats and they all do the same thing so idk what else it could be. I have a buddie that a indie tech thats starting to think its the crankcase breather but idk. Only other thing i could think of myself is a restriction on one side not allowing it flow over to the thermostat soon enough but thats just a random theory that holds no merit . Only time ive experienced a staying cold situation its been the thermostat . But with three different thermostats doin the same thing its gota be something else. I really cant believe that a thermostat could work for 2 weeks then fail sticking open and two of them do the same thing after the exact same amount of time . Im really banging my head against the wall on this one

[theweebabyseamus]

well ive had three different thermostats and they all do the same thing so idk what else it could be. I have a buddie that a indie tech thats starting to think its the crankcase breather but idk. Only other thing i could think of myself is a restriction on one side not allowing it flow over to the thermostat soon enough but thats just a random theory that holds no merit . Only time ive experienced a staying cold situation its been the thermostat . But with three different thermostats doin the same thing its gota be something else. I really cant believe that a thermostat could work for 2 weeks then fail sticking open and two of them do the same thing after the exact same amount of time . Im really banging my head against the wall on this one

Im not sure what the hold-up has been on the pressure test. It takes about 15 minutes and would be very good to get to eliminate some things.

[mrb5_supra_wrx]

Im not sure what the hold-up has been on the pressure test. It takes about 15 minutes and would be very good to get to eliminate some things.Been very busy and haven't had the time to go by my buddies shop. going to get with him and hopefully try to do it before the week's out

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[theweebabyseamus]

Been very busy and haven't had the time to go by my buddies shop. going to get with him and hopefully try to do it before the week's out

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Cant wait!

[bhvrdr]

I'll throw one out there. Heater core or control valve?

https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-heater-control-valve

[theweebabyseamus]

I'll throw one out there. Heater core or control valve?

https://www.yourmechanic.com/article/symptoms-of-a-bad-or-failing-heater-control-valve

Very interesting.... Even if the heater doesn't fluctuate in temp that still follows the behavior of the coolant temp, normal at idle and cool at speed.

[S4'ed]

I don't think the S4 has a heater valve. The heat is shut off by the air-blend flap blocking off all the airflow thru the heater core when the heat is supposed to be off. The coolant always flow thru the heater core.

[timzcat]

Thermostat issue. Feel the upper and lower hoses, if car has been running but they are not hot then coolant is circulating to quickly.
The other possibility is the fan is running when it shouldn't but I would think you'd notice that.

[mrb5_supra_wrx]

Still having issues with this... :( Anyone have any clue? Possible blockage pre thermostat hindering flow keeping it open? Pcv? Idk I'm really at a loss trying to figure this out

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[theweebabyseamus]

You've got the ideas so far, need that pressure test brother. Or try another t-stat from a dealer. You should be able to knock them out in no time now. Lol

[mjt2470]

Do you have any updates on this issue?

I am having almost the exact same issue with my 2011 S4 (same car year/model OP). My issue is that as the car is moving, the heater is blowing hot air but when I stop at a light and idle, you can feel the temp of the blowing air from the heater going down to luke-warm at best (even cold if its a long light).

I took it to an indie shop and I even mentioned the thermostat (which they promptly ignored) and recommended a coolant flush. Their idea was that if they flushed the system it would remove any sediments that were built up and could be blocking the flow.

There was something about their proposed fix that didn't feel right. I felt like they didn't give any real thought to the issue and just threw out an idea. They wanted $300 for this "fix" but wouldn't guarantee that it would work, total guesswork.

Glad I found this thread as I was going to take it to a local dealer and this thread has lots of good information I can query to the dealer.

[mrb5_supra_wrx]

Do you have any updates on this issue?

I am having almost the exact same issue with my 2011 S4 (same car year/model OP). My issue is that as the car is moving, the heater is blowing hot air but when I stop at a light and idle, you can feel the temp of the blowing air from the heater going down to luke-warm at best (even cold if its a long light).

I took it to an indie shop and I even mentioned the thermostat (which they promptly ignored) and recommended a coolant flush. Their idea was that if they flushed the system it would remove any sediments that were built up and could be blocking the flow.

There was something about their proposed fix that didn't feel right. I felt like they didn't give any real thought to the issue and just threw out an idea. They wanted $300 for this "fix" but wouldn't guarantee that it would work, total guesswork.

Glad I found this thread as I was going to take it to a local dealer and this thread has lots of good information I can query to the dealer.Did you mean cold air while in motion? Are you feeling hot air while moving or idle or what ? My issues occur while moving . At idle it gets to temp but when moving the temps go colder or stay cold and I don't get hot air unless I let it idle and get close to temp

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[mjt2470]

Did you mean cold air while in motion? Are you feeling hot air while moving or idle or what ? My issues occur while moving . At idle it gets to temp but when moving the temps go colder or stay cold and I don't get hot air unless I let it idle and get close to temp

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Sounds like my issue is opposite of yours for the most part. Mostly I feel hot air while in motion but cold air at a stop. However, when it dropped to the low 20s for a week my heater was blowing cold almost my whole commute to/from work (about 13 miles each way). We've had an unusually warm season in the Denver metro area and temps have not been below 30s too much (except at night).

[mrb5_supra_wrx]

Sounds like my issue is opposite of yours for the most part. Mostly I feel hot air while in motion but cold air at a stop. However, when it dropped to the low 20s for a week my heater was blowing cold almost my whole commute to/from work (about 13 miles each way). We've had an unusually warm season in the Denver metro area and temps have not been below 30s too much (except at night).That actually sounds more like a thermostat then. I'd do a flush first to save some labor but if you got the funds go ahead and do both

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[b8s4me]

I had the exact same thing happen to me after changing the thermostat, OP. For a few days the temps would take forever to reach operating temps, and would go down if I was on the interstate. The issue was air trapped in the coolant loop somewhere. I just popped the coolant tank open and let her warm up, and filled when air came out and coolant dropped. Did this a few times and the issue never came back.

[mjt2470]

That actually sounds more like a thermostat then. I'd do a flush first to save some labor but if you got the funds go ahead and do both

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Thanks for the advice, I'll be prepared to do both at the dealer!

[s4matty]

Sounds like my issue is opposite of yours for the most part. Mostly I feel hot air while in motion but cold air at a stop. However, when it dropped to the low 20s for a week my heater was blowing cold almost my whole commute to/from work (about 13 miles each way). We've had an unusually warm season in the Denver metro area and temps have not been below 30s too much (except at night).
Let me know what the dealer says.
I'm trying to figure out the same problem on a friend's car.
I've done thermostat and water pump.pcv/oil separator
Complete flush 2 different times,vacuum filled the coolant 2 different times,checked the vacuum pressure for the control valve in heater core hose and the air still blows cold when he comes to a stop.It can sit at idle for 20min with no heat and soon as it rev's to 1500rpm and higher bamm there is heat.Go for a drive and heat is hot and come to a stop and it's blowing cold till it starts driving.
Gonna do head gasket test tmrw I guess.

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[mrb5_supra_wrx]

Let me know what the dealer says.
I'm trying to figure out the same problem on a friend's car.
I've done thermostat and water pump.pcv/oil separator
Complete flush 2 different times,vacuum filled the coolant 2 different times,checked the vacuum pressure for the control valve in heater core hose and the air still blows cold when he comes to a stop.It can sit at idle for 20min with no heat and soon as it rev's to 1500rpm and higher bamm there is heat.Go for a drive and heat is hot and come to a stop and it's blowing cold till it starts driving.
Gonna do head gasket test tmrw I guess.

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sounds wild but let us know how that goes im interested

[jygesq]

Could there be a defective temp sensor? Dealer could easily check by hooking car up to the Audi diagnostic computer.

[mrb5_supra_wrx]

Could there be a defective temp sensor? Dealer could easily check by hooking car up to the Audi diagnostic computer.Temp sensor has been replaced. So not that and there not heat when its low like that. It's still weird to me that if the car site to idle it gets to temp but as soon as you start driving and gets at a good constant speed like 40-60 mph it starts goin back down to the cold line. Car run good without issues for like a month now it's doing the saying cold thing I don't understand it

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[sonic32]

Temp sensor has been replaced. So not that and there not heat when its low like that. It's still weird to me that if the car site to idle it gets to temp but as soon as you start driving and gets at a good constant speed like 40-60 mph it starts goin back down to the cold line. Car run good without issues for like a month now it's doing the saying cold thing I don't understand it

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Faulty thermostat... replace it and problem solved.


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[mrb5_supra_wrx]

Faulty thermostat... replace it and problem solved.


Sent from my iPhone using TapatalkNot the thermostat it's brand new only has 1500 miles on it. The whole thread talks about how it's not the thermostat. I've the replaced the thermostat twice and has not resolved the issues

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[sonic32]

Not the thermostat it's brand new only has 1500 miles on it. The whole thread talks about how it's not the thermostat. I've the replaced the thermostat twice and has not resolved the issues

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I have the same issue with my newly TDI swapped b7 a4. Car runs damn cold, and when it warms up a bit as soon as I start driving it cools down but it’s weird because in every instance I have perfect heat in cabin


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[RWD2quattro]

@S4matty, Not sure if someone has mentioned it but have you cleaned the heater core water plenum drains? If those get blocked with dirt or debris it will affect heater performance. Sometimes you even get water on your floor mats. My heater was acting up recently, clean them up and no more issues.
https://image.ibb.co/iM79yS/raw_appid_Yahoo_Mail_Basic_ymreqid_bac0b72c_f9a6_3 b15_1352_2f0000010000_token_Ob_IIOH0n_N4_Pg_De_XUp xd2_LEGxvb_Ub6i_Pgq_Yng_Oy_M2b_OVcebb_Qq_Ctaw_Za6o 36_D5dlfp_Iu7xr0_WYYt_I4u_EPgzu_Xc_Eu_XYmu4_K2_Es7 _Q5xt7nq1_ild_JA8i3vzfi_Ne_PJFc_LA02.jpg

[mrb5_supra_wrx]

Let me know what the dealer says.
I'm trying to figure out the same problem on a friend's car.
I've done thermostat and water pump.pcv/oil separator
Complete flush 2 different times,vacuum filled the coolant 2 different times,checked the vacuum pressure for the control valve in heater core hose and the air still blows cold when he comes to a stop.It can sit at idle for 20min with no heat and soon as it rev's to 1500rpm and higher bamm there is heat.Go for a drive and heat is hot and come to a stop and it's blowing cold till it starts driving.
Gonna do head gasket test tmrw I guess.

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You figure anything in this matt

[s4matty]

@S4matty, Not sure if someone has mentioned it but have you cleaned the heater core water plenum drains? If those get blocked with dirt or debris it will affect heater performance. Sometimes you even get water on your floor mats. My heater was acting up recently, clean them up and no more issues.
https://image.ibb.co/iM79yS/raw_appid_Yahoo_Mail_Basic_ymreqid_bac0b72c_f9a6_3 b15_1352_2f0000010000_token_Ob_IIOH0n_N4_Pg_De_XUp xd2_LEGxvb_Ub6i_Pgq_Yng_Oy_M2b_OVcebb_Qq_Ctaw_Za6o 36_D5dlfp_Iu7xr0_WYYt_I4u_EPgzu_Xc_Eu_XYmu4_K2_Es7 _Q5xt7nq1_ild_JA8i3vzfi_Ne_PJFc_LA02.jpg
The issue on his car was drivers side headgasket.
He later told me he overheated it when a rock hit his charger he and he drove home.
It's been fixed now
And not a fun job that was.

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[S4'ed]

S4matty : So I assume the headgasket was letting cylinder pressure into the cooling system? (Could you verify this from looking at the head gasket?) Can you post a picture of the gasket?

I have the same issue with my S4, where the heater gets cold at idle. I also have the water gurgling sound behind the dash, which is the air pocket that blocks heater coolant flow at idle ( the water pump does not have enough flow to push the air pocket thru the heater, until the engine RPMs are increased.) Basically the bad head gasket causes pressurized air from a cylinder to get pushed into the cooling system, which then collects at the high spot of the system, where the heater hoses go thru the firewall. I have been suspecting the head gasket for a while.....but everyone on this forum has claimed that this is not an issue with the 3.0T...see below.

https://www.audizine.com/forum/showthread.php/625289-Anybody-have-a-head-gasket-fail-on-a-3-0T?highlight=head+gasket

[theweebabyseamus]

For what its worth, my t-stat is acting up again. This will be the forth replacement.

1st instance: car wouldn't get to temp, purchased VW OEM part, issue self-resolved after a few weeks.

2 instance: car wouldn't get to temp, replaced with the VW part I still had from before.

3rd instance: occurred a couple of weeks after the previous replacement. Purchased a t-stat from a local Audi dealer.

4th instance: about 13 months and 15k miles later, the Audi part failed. Purchased an OEM t-stat from I BELIEVE RM Euro towards the end of 11/2018. Anfd a new coolant cap.

5th instance: car has been not getting to temp as fast for a few weeks. This morning it finally wouldn't get to temp.



I'm obviously happy the car is still driveable, but can't help wondering what else could cause this. I have replaced the water pump but not the PCV yet, but soon. The PCV is the only variable I can think of that could affect the cooling system as I cant think of anyway a head gasket failure or incorrect bleed process could manifest these repeated symptoms, especially since the new t-stats work for a bit.

[S4'ed]

I don't think the PCV has anything to do with your problem. The PCV just has a 3 inch long passage through it for the coolant to flow (to heat the PCV unit so that the oil separator doesn't freeze in the winter). It is really no different than any other plastic pipe in the cooling system. If this passage fails (cracked plastic), the coolant either leaks out into the valley V of the engine, then drips on the ground, or the crack occurs in a place that allows coolant to leak into the crankcase, mixing with the engine oil. I can't see how this PVC passage can cause the engine temperature to be too low.

[theweebabyseamus]

I don't think the PCV has anything to do with your problem. The PCV just has a 3 inch long passage through it for the coolant to flow (to heat the PCV unit so that the oil separator doesn't freeze in the winter). It is really no different than any other plastic pipe in the cooling system. If this passage fails (cracked plastic), the coolant either leaks out into the valley V of the engine, then drips on the ground, or the crack occurs in a place that allows coolant to leak into the crankcase, mixing with the engine oil. I can't see how this PVC passage can cause the engine temperature to be too low.

I agree with you, but its the only other thing I can think of besides getting 4 bad t-stats. Lol

[S4'ed]

When you are installing the thermostat, are you sure you are getting the pin inserted into the hole at the bottom of the thermostat housing?

[theweebabyseamus]

When you are installing the thermostat, are you sure you are getting the pin inserted into the hole at the bottom of the thermostat housing?

I BELIEVE so. I don't really know how you'd check or verify. And I would think that would manifest immediately.

Edit- what I will say is the last t-stat I pulled out had one of the three internal tabs broken and I don't think that was the first.

[theweebabyseamus]

The issue resurfaced with this new OEM t-stat. My next step is to buy a vacuum bleeder and see if that helps. If I'm getting air in the system I'll troubleshoot that when the time comes.

[morris39]

The issue resurfaced with this new OEM t-stat. My next step is to buy a vacuum bleeder and see if that helps. If I'm getting air in the system I'll troubleshoot that when the time comes.
A long shot that costs almost nothing. Tighten the coolant reservoir so you hear 3 clicks. Someone (dealler?) did not fully tighten and the level dropped from MAX (i think) to just above MIN line in about 4 months and the oil temp struggled to reach 100 deg. C in cold weather. This is on 2.0TFSI

[theweebabyseamus]

SO, I did what some have said and left the res cap off. I let it run with the heater on HI and fan at 1 and around 8 mins in the coolant started to raise. When it seemed like it would over flow I shut the car off and it bubbled. The next morning the t-stat worked BETTER but not correctly. Got to temp and went down a little. I'm likely going to order a vacuum filler but it was encouraging....unless I have air getting into the system.

- - - Updated - - -


A long shot that costs almost nothing. Tighten the coolant reservoir so you hear 3 clicks. Someone (dealler?) did not fully tighten and the level dropped from MAX (i think) to just above MIN line in about 4 months and the oil temp struggled to reach 100 deg. C in cold weather. This is on 2.0TFSI

Thanks, but mine only goes one click.

[Audi_here]

there is a vacuum valve on the front of the block under bank2 cyl head, this actuates the water pump impeller, there is a vacuum line from this valve to the water pump. when the car is cold the impeller is pulled in and is disengaged to let the car warm up, when it gets hot the valve closes and lets the impeller out and engages to pump coolant through the engine to cool it. if this valve is sticking it may cause this issue. just a thought. usually when this valve goes bad the car will take forever to heat up or wont at all. but other than the thermostat and water pump there isnt much else that controls cooling and heating of the engine. but as for cabin heating issues the coolant control valve behind the engine and bolted to a bracket on top of the bellhousing commonly fails causing no heat or very little. it wont throw a code either.

[igotag]

Any update to this? I just replaced my thermostat and now I’m having this same issue.


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[theweebabyseamus]

After doing the open coolant cap trick (I did it again), I haven’t had any issues since.

[igotag]

After doing the open coolant cap trick (I did it again), I haven’t had any issues since.

Just bleed with the over flow cap open?


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[theweebabyseamus]

I had the exact same thing happen to me after changing the thermostat, OP. For a few days the temps would take forever to reach operating temps, and would go down if I was on the interstate. The issue was air trapped in the coolant loop somewhere. I just popped the coolant tank open and let her warm up, and filled when air came out and coolant dropped. Did this a few times and the issue never came back.

Yeah, I just ran the heater on HI and lowest fan speed and started the car with the cap off. Eventually some bubbles came out. Left the cap open overnight and added coolant as needed. Tried this process a few times and its been good since.

[igotag]

Yeah, I just ran the heater on HI and lowest fan speed and started the car with the cap off. Eventually some bubbles came out. Left the cap open overnight and added coolant as needed. Tried this process a few times and its been good since.

Ill give it a few tries.