i've searched the forums and i've applied what i've learned so far, but i'm still having engine/coolant overheating issues. people here have come through for me in the past - hoping someone can assist with this one...

here's the issue: as the weather warms up (anything over 50/60 degrees) outside, my temp gauge keeps climbing towards "H" - sometimes it will be 1 tick past the middle (somewhat normal), but most of the time it's 2 ticks or buried on "H". during idle (which i understand the car will run a bit hotter since no air is being forced into the radiator), this happens quite frequently. recently, the needle has been climbing to "H" (and stays on "H") only after driving 2 or 3 blocks! over the past couple weeks, three times i've had the water/coolant symbol flash on the center display (once that comes on, i immediately stop the vehicle and let it cool down). the weird thing is, while i'm driving and while the needle is still buried on "H", all of sudden, things will go back to normal and the needle will drop down towards the center of the gauge - car runs normally for maybe an hour and the problem reappears. this problem started to happen around August/September of last year - the weather started to cool down so i never had the problems during the Fall or Winter here in Chicago.

i've used the A/C readout for coolant temp and when the gauge is in the middle, i'm at around 96 to 102 degrees. when it's 2/3rds of the way to "H", it's around 115 degrees. when it's buried on "H", it's at 121 degrees. the car's performance degrades when it's on "H" as well - i've verified that both of the fans are working up front (both kick in when i'm at "H"; both kick in when the A/C is on). also, when i got my timing belt replaced recently (@ 70K miles), the water pump and thermostat were replaced as well. when i had the original, black coolant temp sensor in (first 3 years of ownership), i never experienced this problem. i put in the green sensor and the problems appeared (not sure if that's associated though). i've gone through 2 green coolant temp sensors already, hoping that would resolve the issue. i'm about to put in my 3rd one in tonight to see if it fixes things. i'm searching for the old black version as well. btw, no fault codes to be found.

is there another sensor that needs to be checked and/or replaced that i'm missing? or is there another area i should be looking at? any way i could use the VAG-tool to help diagnose this cooling issue? it's a 2001 225 (AMU, April 01 build), original owner, and lightly modified.

sorry this post is long. appreciate any thoughts or input before i drag her to the dealership or my local VW/Audi shop.

thanks,
chris

 

levels are up to snuff?

 

I'm betting on thermostat!

 

Also, make sure that OEM coolant was used during the tbelt change and that it was mixed properly.

 

and coolant level is fine from what I can see in the resevoir.

I forgot to mention that part in my long post.

Thanks though.

 

and have them recheck it or replace it - won't hurt. Can't say that the coolant was mixed properly though - I just assumed it was since they've done this before.

Thanks for your input.

 

looking at it, but if it worked well for a little while and all of a sudden started overheating, I would suspect the T-stat. Basically, it doesn't open and so heated coolant never leaves the engine to be cooled off in the radiator. Which thermostat did they use? Was it done by Audi dealer? Check to make sure that they used OEM coolant and that they mixed it with water. If they tell you that coolant comes pre-mixed...I'd be cautious.

 

Based on what you've told me, maaliish is prolly right, bad Tstat.

 

sounds like your thermostat is sticking in the closed position.

 

The job wasn't done by an Audi Dealership, but an independent Audi/VW/Porsche shop (with former Audi techs). Actually, it was done by a friend of mine who works there so I trusted him.

Coolant is reddish/pink (Pentosin); I was told they used an OEM thermostat.

Well, thanks again for your input!