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View Full Version : What would cause slight overheating at low speeds and idle



2.7taudi
11-23-2014, 05:43 PM
So the story starts with a leaky water pump. I go to the mechanic and get the water pump, thermostat and housing changed.

IMMEDIATLY car starts heating up past the middle mark. It goes between the middle mark and one mark past the middle. In between those 2 marks.


It happens all the time but at idle it gets worse. And starts to cool a little bit once I start moving. It is still not perfectly centered. But less than it is at idle.

It happens once the engine has been running a while.

Example
Cold start then temp needle rises to perfect center. Once it has been warmed up as in the oil temps reach 175-200F then the coolant temp starts creeping to the Hot side.

I have vag com the car and the temp difference is 6-8 degrees Celsius. At dead center it's at 96C (same as my 2.7t) then when at its highest point the temp is 102-105

I have changed the coolant temp sensor and the connector as my mechanic declines to acknowledge that it is his fault or his parts fault even tho it happened r8ght after the repair.. So that's new...

What do you guys think???

Saskwatch
11-23-2014, 05:52 PM
sticky thermo stat, partial clogged heater core, clogged rad fins or condenser fins, (poor air flow through radiator)...
Poor performing cooling fan, many avenues to take. take ur pick.

pbcrazy
11-23-2014, 05:59 PM
Sounds to me like you need to bleed the system

2.7taudi
11-23-2014, 06:15 PM
Sounds to me like you need to bleed the system
Wouldn't the bubble cause the cause to run normal and then heat up when the bubble approaches or am I talking nonsense? Basically once the needle rises above the middle it never perfectly centers. And when I turn the heat on it cools perfectly.

2.7taudi
11-23-2014, 06:17 PM
sticky thermo stat, partial clogged heater core, clogged rad fins or condenser fins, (poor air flow through radiator)...
Poor performing cooling fan, many avenues to take. take ur pick.
How can I look at if the thermostat is faulty? The fan is fine. The electric fan does not kick in so the car is not completely overheating. It does however turn on when the ac is on and at 2 different speeds as well.

pbcrazy
11-23-2014, 06:19 PM
Wouldn't the bubble cause the cause to run normal and then heat up when the bubble approaches or am I talking nonsense? Basically once the needle rises above the middle it never perfectly centers. And when I turn the heat on it cools perfectly.

Bubbles can move or stay put and limit coolant flow, you can also have more than one which can cause some pretty weird symptoms. Regardless, after any cooling system repair you should bleed the system. Turn the heater on high and pull the passenger side heater core hose (next to battery) off until the small hole is off the nipple. Hold it off until a small stream of coolant is constantly coming out. It might not be a bubble, but it is definitely the easiest thing to try with overheating problems

Saskwatch
11-23-2014, 06:27 PM
I'd hate to think he paid a shop for the repair, and they didn't do the usual warm up/bleed routine. Especially with a water pump replacement/tstat swap.
You can check to see when it opens via infra red laser heat gun checking temps on either side of the thermostat to see when it is opening. (at what temp)

bhusted
11-23-2014, 06:33 PM
Fan clutch? Since it cools down when you start moving, I would guess that the viscus fan clutch is shot.

pbcrazy
11-23-2014, 06:37 PM
Fan clutch? Since it cools down when you start moving, I would guess that the viscus fan clutch is shot.

If it's not an air bubble this would be my guess. I'm just hoping for his sake it's an air bubble, the fan clutch is not the most fun job in the world

2.7taudi
11-23-2014, 06:45 PM
Fan clutch? Since it cools down when you start moving, I would guess that the viscus fan clutch is shot.
Actually I just came off the highway at 70 mph and the temp stayed above normal. Can't be the fan. I'll edit the post

Saskwatch
11-23-2014, 06:46 PM
on mine it was the electric fan lagging... i got lucky. LOL

2.7taudi
11-23-2014, 06:46 PM
What I mean is that the temperature fluctuates as I'm idle to acceleration then at constant speed it stays at an inflated temp. Then when I coast, off the ramp it cools a bit. Then heats up again if idling for too long....

2.7taudi
11-23-2014, 06:49 PM
The temperature is NEVER back to normal once it heats up. But it fluctuates. The temp is dead center from a cold start for about 5 miles then it starts flucating..

pbcrazy
11-23-2014, 06:50 PM
What I mean is that the temperature fluctuates as I'm idle to acceleration then at constant speed it stays at an inflated temp. Then when I coast, off the ramp it cools a bit. Then heats up again if idling for too long....

Air bubble, fan clutch, or both. The fact that is higher than middle at speed makes me lean towards bubble though. Generally a bad fan clutch will let the temp rise at idle as it doesn't pull in enough air to keep it cool, but at speed the fan doesn't need to do much at all as there is plenty of air moving already.

chris164935
11-23-2014, 06:52 PM
Have you not tried to bleed the coolant system yet? I had the EXACT same problem and I bled the system and everything was perfect after that.

2.7taudi
11-23-2014, 06:55 PM
How do I bleed the system? I have heard pulling the hose near the battery actually pull in air and some say it releases the bubbles...

2.7taudi
11-23-2014, 06:56 PM
I have opened the coolant tank and let it idle till the OIL temp was 200+ and it didn't pass the temp one bit. As soon as I put the cap back on the tank it started to creep towards the heat side...

Saskwatch
11-23-2014, 06:57 PM
take it back to the shop, talk to the owner, you paid for repairs, and you still do not have a properly functioning cooling system. you swapping out a sensor, that has nothing to do with charllie mcknuckle-draggers repair. but make sure you say, "I have heard of problematic sensors and took it upon myself to swap it out", and the same problem occurs. And if nothing then, ask if your mechanic vacuum filled the system, and if he didn't, ask why would he not, when every one worth their salt as an audi mechanic knows to vacuum fill the cooling system.

pbcrazy
11-23-2014, 07:00 PM
How do I bleed the system? I have heard pulling the hose near the battery actually pull in air and some say it releases the bubbles...


Turn the heater on high and pull the passenger side heater core hose (next to battery) off until the small hole is off the nipple. Hold it off until a small stream of coolant is constantly coming out.

Opening the coolant expansion tank won't bleed the system as it is not the highest point in the system (unless you hold it above the heater core)

Drifter420
11-23-2014, 10:23 PM
If the coolant wasn't mixed correctly it's screws with the boiling point which can cause hot or cooler running temps. Check your fan clutch tho it could be going bad

Saskwatch
11-23-2014, 10:26 PM
hell make sure the shop used the right coolant at this point, if they cant even bleed the fuckin system for ya.

2.7taudi
11-24-2014, 04:19 AM
The coolant os correct. This guy used to work at the dealer and has done a lot of my repairs and this is the first I've encountered a problem.

I also thought it was the coolant mixture and I removed 1.5Q from coolant tank and added pure g13. No changes.
And actually when I drove it to him with a leaky water pump it was about 70% water lol and it didn't overheat once.

walky_talky20
11-24-2014, 06:21 AM
You have failed to mention what year the car is and what engine it is equipped with.

Based on symptoms, I would say it sounds like a faulty thermostat or clogged radiator. A faulty clutch fan is possible, but in that case I would expect the temp to only raise at idle, and then retreat almost immediately with vehicle speed. The fan and clutch are pretty easily checked, though. So that would be step 1.

I would be even more suspicious of the thermostat if it was changed along with the pump. This would be more commonly done on an AEB or ATW (97-2000 1.8 liter turbocharged engine) due to the thermostat being mounted directly in the water pump housing. If it was replaced with an aftermarket thermostat, I would be inclined to swap it out for a new OEM t-stat.

It is also possible that the new water pump is lousy at low RPM (idle) speeds due to bad impeller design or manufacturing error. I would say that this is pretty low probability, though.

2.7taudi
11-24-2014, 06:33 AM
The vehicle is ATQ 2.8. What I'm not getting is how it can be anything else besides the 2 parts replaced or bubble. As this was not happening before the repair.

My main concern is how do I get my mechanic to acknowledge it is a faulty thermostat. How do I know he won't pin the problem on something else.

walky_talky20
11-24-2014, 06:36 AM
Gotcha.

If it was a bubble, it would have worked it's way out after a couple hot/cold cycles and topping off the coolant. If it was completely air locked, it would be overheating a lot worse.

What brand t-stat is installed?
Did you get a new t-belt/tensioner too?

I think he should understand it's something he did. You brought it in for a leak, he changed parts, now it overheats. Pretty simple to understand it's one of the parts, or install issue (ie: not bleeding). As a customer, you shouldn't need to worry about what it is or isn't. Just take it back and tell him how to reproduce on a test drive. Pick it up when it's fixed. He should be very inclined to fix it for you. And happy that you didn't cook the engine before bringing it back (leaving him with some responsibility for that damage).

2.7taudi
11-24-2014, 06:48 AM
Gotcha.

If it was a bubble, it would have worked it's way out after a couple hot/cold cycles and topping off the coolant. If it was completely air locked, it would be overheating a lot worse.

What brand t-stat is installed?
Did you get a new t-belt/tensioner too?

I think he should understand it's something he did. You brought it in for a leak, he changed parts, now it overheats. Pretty simple to understand it's one of the parts, or install issue (ie: not bleeding). As a customer, you shouldn't need to worry about what it is or isn't. Just take it back and tell him how to reproduce on a test drive. Pick it up when it's fixed. He should be very inclined to fix it for you. And happy that you didn't cook the engine before bringing it back (leaving him with some responsibility for that damage).
I wish mechanics were that easy to work with. They are the most friendly people when you come in for a repair but are insanely difficult to work with when there is a problem related to the repair.


The brand of the stat I'm not sure. He says he uses oem parts. Another thing that boils my blood. All mechanics charge full retail prices for oem parts when I can get the original audi stamped parts for same price. The point of oem is to be cheaper than OE parts..

Just venting...

walky_talky20
11-24-2014, 06:55 AM
As long as you are willing to wait and pay, I don't think any mechanic should have issue with you demanding genuine OE parts. Shops are able to get a discount from the dealer parts dept. Usually on the order of 10-20%. So he would still be able to mark up the parts and make some money, whilst actually getting the "good stuff" and not have to worry about fixing it again when chinese copy of part "x" craps out.

Saskwatch
11-24-2014, 07:59 AM
that and any (decent) mechanic should be receptive to what your car is doing after a repair, not saying "there is no way in hell I caused that". I guess it was the mouse in the mother ******s pocket who did the repair?

Saskwatch
11-24-2014, 09:21 AM
I wish mechanics were that easy to work with. They are the most friendly people when you come in for a repair but are insanely difficult to work with when there is a problem related to the repair.

most are, it's the hacks/parts changers that get all defensive and but hurt.