hey guys, i am really new to these newer Audi's having owned a 1988 Audi 80 quattro. my question is when i first bought the car i took it into the licensed vw/audi repair shop in my town and had the timing belt, thermostat, water pump and radiator replaced because the car had 200k on it and figured i should just do it all as a precaution. 6 months later i am having a issue of sometimes and its not all the time after the car has been sitting for 12+ hours when i go to fire her up at cold it it will read at operating temp then as i drive it will say its over heating almost going to the 'H' on the gauge. i know its not over heating because everything is cold (hoses, radiator, heat from the heater core not blowing hot air.) and once it is running it doesn't feel hotter than it normally would be. after awhile it seems to reset itself but i don't like the idea that if it does go up all the way i have heard the computer can shut the motor off.

my question is and i hope this doesn't have to do with the ecu. could this just be a faulty temp sensor? or could it be the thermostat was bad? i really love this car to death but it is extremely hard to work on. any advice?

 

The coolant temp gauge like many Audi parts are made out of recycled soviet left-overs(super cheap-***). They have been through a few revisions that I know of, so if you're on the original version that's known to be faulty, I'd replace it.

When mine went out it would always read cold, then shoot up to the middle, then go dead again. So I can't say for sure its your temp sensor.

The other thing it could be is the cluster, as they are also unreliable particularly the LCD screens procured from Chinese production reject bins. But this is less likely.

The temp sensor is a 2 part sensor. Often when they fail it's one side/part. As I understand it one part reports to the gauge and the other the ECU. There is a way to see what temp the ECU is seeing through the climate control screen. Go to: http://www.audiworld.com/tech/int6.shtml and follow the procedure to check temperature. Then you'll know for sure if your ECU is getting the right temp and probably know for sure its the temp sensor and not the thermostat.

Good luck.

 

yeah i just went on a long drive to make the "gauge" and nav led screen say its over heating. and i did that sweet ecu trick you pointed out and the ecu says the coolant temp was at 48c which is 118f which as i'm sure is not anywhere neer over heating and also the car didnt turn off when i reached maximum temp on the gauge. so im sure its just that is out because the car was running fine, hoses again felt no where out of the normal as well as radiator was hot but not to the point of over heating just normal.

thank you theflash for showing me that awesome trick and now i have a place to start from. just have to figure out where to go from there

 

Change your coolant temp sensor. Theirs notorious for failure. Be sure you get a new o-ring with it and also that when you take the old sensor out, the old o-ring comes out too, or you'll have a volcanic coolant leak under pressure.

 

Glad I could help. BTW, 90c is about normal operating temp. ImTheDevil is right, definitely replace the temp sensor, after reading what you described.

 

it wasn't a long drive, just enough to get the gauge to say it was over heating which was a surprisingly 15 minute drive. and after sitting for 15 hours now it is still saying it is a 3/4 up on the gauge. its very annoying when the dash starts beeping at you.

but were is the sensor located at? my haynes manual says its on the back side of the motor under were the air intake goes into the intake manifold granted it is the manual for the passat and a4 96-01. but i noticed one on the bottom radiator hose. did they change were it is between the 12v and the 30v? and i know if it is ether there is not allot of room to change it ether way but im hoping its on the lower radiator hose.

 

The one on the bottom radiator hose controls the electric fan speed, the one you want is back against the firewall on the passenger side of the engine just behind the engine block. Yes its down under the air intake tube and just outboard of the throttle body. Its held in with a C clip that you have to pull out towrds the firewall and then the sender just pulls straight up.

 

When you get your new sensor be sure to also get another C clip and o-ring. The o-ring has been compressed and baked and may not seal right and the C clips get brittle from heat and can break fairly easily.