Coolant temperature goes up when driving uphill

[jaynav33]

I have a 2002 a4 1.8T.

So about 2 months ago my thermostat housing started to leak.. so I decided to change that out and also my heater core since I haven't had hot air in a couple years.. so a month goes by and car is running great, early this month I noticed a little puddle of coolant on street. Checked it out and looks like my water pump has a small leak that drops on floor when the car is left cold over night..

Fast forward to this past Thursday night I noticed my temp gauge for the first time ever rise above the 1/2 way mark. When im driving on leveled road or downhill it goes back down to normal. I get home and park and noticed my fans are on (took about 4 minutes for fans to turn off). My coolant overflow tank isn't low, im starting to think I may have. Clogged radiator and most likely air In the system since my water pump has a slow leak... any thoughts guys? I'd appreciate it

[jaynav33]

Damn, over 160 views/hits and no one has any ideas??

[ADCS]

I think you answered your own question :-)
Fix the leaks and see what happens.
Original rad? replace it for sure.

Uphill will be high engine load so the temp rise makes sense.

[ozMatt]

Is it a stock water pump with the plastic impeller? If so the impeller could be slipping on the shaft, causing reduced flow.

...or is it an aftermarket water pump with metal impeller? If yes, and it's leaking, I'd say replace it asap before the bearings go and it strips your timing belt.

[BARRY]

as others have said...if your water pump is still leaking, replace or repair it. if you have the original radiator, replace it.

[jaynav33]

Yes I am going to do the timing belt/water pump in the next week or so as soon as I get the parts from ecs tuning and I am also gonna put a radiator just to be safe. I already put a radiator when I did my first timing belt because it was leaking. I currently have 186k miles, drove the car around the streets for about 10 minutes and parked it back at home. Temps didn't rise above 1/2 because it was mostly leveled roads, did notice my coolant level in the overflow tank did rise when hot and my upper radiator hose has pressure and gurgling sounds on all coolant lines when I parked it and turned vehicle off..

[Protection]

I'd be willing to wager that if you have coolant leaking out, you have air getting into the system. The air pocket is the reason your car overheats--it is preventing the coolant from flowing normally. How many miles are on your current radiator (you said you replaced it previously)? I don't know that that is the problem. I had 150k on my B5 S4 radiator with no issues.

The gurgling sound you hear is the air expanding as the coolant cools down and the pressure in the system drops. As the air expands it makes that gurgling sound. So that fact you hear gurgling, confirms air in the system.


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[jaynav33]

My first radiator got replaced around 95k miles and that's when I just decided to do the timing belt and water pump with it. The plastic side part of the radiator had a crack, now also im cool with an Audi mechanic and he actually does all the big repairs on my car and he did the t-stat and heater core/flushed coolant at his home . He did say my coolant system was so dirty with some nasty black and sediment (due to clogged heater core) that's why maybe I suggested changing radiator if any of that crap is trapped in there..

[old guy]

The normal operation of a mapped cooling system is to reduce the block temperature when it is under load. On a long upgrade I have seen my rear CTS drop to as low as 179°F. If yours is increasing I can think of three possibilities. Failed heating element in the thermostat housing, impeller slipping on the water pump, or a head/head gasket issue.

First check to see if you have any DTC’s relating to the mapped cooling system function. Something like a P1296. If you do, you can use VCDS to determine if it’s a faulty signal to the heater or the heater itself isn’t working.

The next thing I would suggest is to perform a block gas test. I suspect this will probably be your problem. You are getting combustion gasses into your cooling system. This would be caused by a failed head gasket or cracked head. Unfortunately that was my problem several years ago.

Good luck!

[jaynav33]

Yes, I believe it should be water pump related. I doubt its head gasket related, I don't get any white smoke out of my exhaust on cold starts that smell sweet and both my oil (not milky) and coolant colors are normal.

And I have 0 DTCS currently as well, only time i've ever had a DTC for cooling system was around 50k miles when the CTS sensor in the rear coolant flange went bad and my fan would turn on randomly when cold. I replaced that sensor again around 130k miles when I replaced the leaking rear coolant flange and valve cover gasket was done at that time also.

My tech also replaced all 4 spark plugs last month when he changed out the heater core/t-stat and said he doubts its head gasket, he didn't find coolant in any of the cylinders and said my car would be running like shit also if that were the case.

I have never replaced the other coolant sensor though, the one that sits on lower radiator hose that we pull out to drain the coolant. Should replace that also as well?

Thanks!

[jaynav33]

Pics of when I did valve cover gasket and chain tensioner seal around 40k miles ago (186k miles now). I remember there was a little bit of oil on cylinder #4 because of the leaky valve cover gasket.

[old guy]

I doubt it’s the lower CTS causing an overheat condition. The ECM utilizes the rear CTS reading along with engine load requirements to determine the thermostat heater duty cycle. The lower temperature sensor is simply used to determine if the thermostat is reacting properly to the ECM input. If something gets out of whack the default is to apply full power to the heater. When that happens you will get a DTC for the mapped cooling system.

Since you aren’t getting any DTC’s for an open circuit or a mapped cooling system error you really need to look elsewhere. I believe you have a mechanical issue and not a controls issue. That leads back to a slipping impeller or a cracked head. A cracked head probably won't exhibit a mix of oil and coolant nor will it necessarily put out white smoke or smell sweet.

You can either replace the water pump or remove the thermostat and reach your fingers in to see if the impeller is slipping. You can also check block gasses for a possible cracked head. Are you losing any coolant at all?

[jaynav33]

Oh Okay, and no I actually am not losing coolant or atleast not enough to where i notice it. Have only topped it off once and it was like 4 ounces of distilled water that I added to make it back to the max level and that was a few days after I got that service done. Just a tiny puddle accumulates on floor and a few drops of pink g13 on oil pan.

[jaynav33]

Update on my thread.

So my Audi mechanic came over to my house on Saturday and Replaced the water pump, timing belt and radiator. Everything went smooth but again the coolant temperature would go over 1/2 ways and he connected his Vagcom and saw that there was a thermostat fault in the system.
So he told me the aftermarket thermostat (ECS Kit with upgraded Billet j-plug) we put in in July is most likely faulty or there is still air in the system. He told me to take off the coolant cap from the expansion tank overnight and see if it would burp out any excess air out the system.
Sunday morning i put the cap on and started the car and drove it around the neighborhood for about 5 miles and the car didnt overheat, so i decided to drive it to work.10 hours later When I was driving back home though the temperature got to 3/4 for a bit and then cooled back down after i got him on phone and told me to turn on the AC in the car. So he said to Buy the Oem thermostat from the dealership because hes pretty sure the T-stat is partially stuck open..
Drove the car around the neighborhood this morning for about 3.5 miles and the temperature again went a tad bit over 1/2. So I'll update you guys when we throw in the OEM t-stat to see if thats the issue..

[imnuts]

So he said to Buy the Oem thermostat from the dealership because hes pretty sure the T-stat is partially stuck open..

Not to say that the thermostat isn't the issue, but if it were stuck open, you'd have issues keeping the coolant at temperature, not with the coolant getting to hot. It may be stuck partially closed though. There is a thread here though that gives instructions on how to test a thermostat to see if it's working, if you wanted to test yours before buying a new one. Also, are you sure all of the air is out of the system?

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[jaynav33]

*UPDATE*

Looks like the issue was the Aftermarket Thermostat that came with the "Thermostat Replacement Kit With ECS Billet Aluminum J-Plug", when the mechanic pulled out the T-stat housing and compared it to the OEM one I bought at the dealership. Looking inside the actual housing and compared the t-stat spring it was way off compared to the OEM one.

Already put 60 miles on vehicle and so far the temp gauge has stayed right in the middle.. Also when replacing the CTS that's in the rear coolant flange the o-ring was so flat and busted like it was going to crumble anytime..

Now I have to see and return the T-stat to ECS Tuning and get refunded ...

[egovreau]

*UPDATE*

Looks like the issue was the Aftermarket Thermostat that came with the "Thermostat Replacement Kit With ECS Billet Aluminum J-Plug", when the mechanic pulled out the T-stat housing and compared it to the OEM one I bought at the dealership. Looking inside the actual housing and compared the t-stat spring it was way off compared to the OEM one.

Already put 60 miles on vehicle and so far the temp gauge has stayed right in the middle.. Also when replacing the CTS that's in the rear coolant flange the o-ring was so flat and busted like it was going to crumble anytime..

Now I have to see and return the T-stat to ECS Tuning and get refunded ...

I think ECS may want to rethink that kit and use a different thermostat housing. I bought the same kit and the thermostat failed after only 3500 miles

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[jaynav33]

I think ECS may want to rethink that kit and use a different thermostat housing. I bought the same kit and the thermostat failed after only 3500 miles

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Yes I agree, if you had issue with that same kit as I did. If I were them I'd just drive the cost of the Kit and have it be an OEM T-stat with the upgraded J-plug...

[egovreau]

My thermostat was functioning just fine. I just wanted to swap it, and the J-plug, out while I was down in there anyway.

So, when the new one failed, I still had my OEM thermostat sitting on a shelf (I just couldn't throw it out).

As it was still in the warranty period (just barely), ECS sent me a replacement. Unfortunately, it was the same as the failed part, but if I ever need a temp spare, I'll have one.

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[5ktq]

What brand is the bad thermostat?

[egovreau]

What brand is the bad thermostat?

Mine was HT. Hamburg-Technic

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[jaynav33]

What brand is the bad thermostat?

Mine was also HT aka Hamburg-Technic.. That's the one they throw in with that T-stat kit with the upgraded J-plug

[jaynav33]

My thermostat was functioning just fine. I just wanted to swap it, and the J-plug, out while I was down in there anyway.

So, when the new one failed, I still had my OEM thermostat sitting on a shelf (I just couldn't throw it out).

As it was still in the warranty period (just barely), ECS sent me a replacement. Unfortunately, it was the same as the failed part, but if I ever need a temp spare, I'll have one.

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Yeah a few weeks ago I called ECS and they emailed me some return forms to fill out and I am going to send them back that "HT" Hamburg-Technic and get a refund back hopefully

[egovreau]

Yeah a few weeks ago I called ECS and they emailed me some return forms to fill out and I am going to send them back that "HT" Hamburg-Technic and get a refund back hopefully

Chances are, they'll probably send you a replacement part. But, you could probably decide you don't want it and request a return on that one. Never really thought of it before.

They do generate a new order so it's possible. There might be a timeline on it though.

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[jaynav33]

Chances are, they'll probably send you a replacement part. But, you could probably decide you don't want it and request a return on that one. Never really thought of it before.

They do generate a new order so it's possible. There might be a timeline on it though.

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Yes, I believe the lady said they would just refund me and take it back as a defect. Told them I was gonna keep the Billet J-plug and the other hardware and send them thermostat only. I would be happy just getting back the $69.99 that they price the HT brand T-stat alone without the kit. Also noticed that the OEM one from the dealership has the Audi/Vw logos AND MAHLE logo. Looks like they make it for OEM