I've fixed a few issues on my 01 a4 quattro I just bought to get it running pretty good. Changed crankshaft sensor, coolant temp sensor, fixed a few shorted wires, and a few other misc things. My question is when I am driving the temp gauge will be a little bit past the halfway mark. If I let it sit for a while the gauge will go to the mark past the halfway mark. Which is obviously normal since there isn't as much coolant getting sucked through the engine and there is no airflow going to the radiator. But the weird thing is I used the on board diagnostic codes through the climate controls and put in code 51 which is for coolant temp. It read 90 deg celcius (194 deg F) whether the gauge is at the halfway mark or at the dash above the halfway. Seems odd to me. Anybody know what this problem could be... Thanks

 

Could be the Thermostat maybe?

 

Yeah, that doesn't sound normal to me to have the gauge go to the mark past the halfway mark. Mine always sits on the middle mark when the engine's at operating temp.

 

I really don't see how a thermostat can cause my problem. My problem is my temp is ready 90 deg celcius on the on board diagnostics on the climate controls, but the temp doesn't change when the gauge moves up a dash... So where ever the temp on the climate controls gets its reading from, which I assume is the coolant temp sensor I just replaced, that reading should be accurate. Is there any other sensor that controls the gauge which may be off? Or is the cluster/gauge possibly damaged?

 

Theres two elements in the temperature sender, one for the ECM, and one for the gauge cluster. I woul assume the climate control module gets its reading from the ECM signal, and the other one only works the gauge. You could have a bad gauge element, or the wiring between the sender and the gauge cluster could be damaged, or the cluster itself may be bad.

 

So do you think it is safe to assume that the temp from the climate control is accurate and my car is actually running at 90 deg C, which is perfectly normal? Even if the actual gauge is a little off it never goes past the first mark after the halfway one so it is not like the gauge is saying i'm really overheating.

 

So i found out the temp gauge on the climate control is not accurate. The car overheated today and the gauge on the cluster was 2 marks past the half and the coolant resevior was bubbling and smoking. The gauge on the climate control still read 90 deg celcius. I'm not sure why the coolant was bubbling and why it overheated. I drove to a gas station put some water in a let the engine run with the cap off for a few mins. I began to drive it home there was no heat. Started to overheat again so I pulled over poured some more water in a let it sit with the cap off. Drove it again with the cap on and the gauge never went more than a little bit past half way mark and heat worked. i drove about 20 miles like this. I'm going to drain the radiator and bleed the system.. I don't know what else the problem would be.

 

UPDATE: Flushed radiator and bled the heater core. Drove the car about 15 miles and the temp gauge sits at halfway or slightly above halfway when cruising. At red lights it will go almost to the mark past the halfway line. Temp on the climate controls reads 90 and will not move above of below 90. It will read below 90 when the car is completely cold and will gradually go up to 90 deg. Also the secondary auxiliary fan never comes on. Not with the A/c or not when the car was overheating. I'm guessing the reason is it will only go on when the car gets above 90 deg celcius and the ecu obviously never thinks it is getting hotter than that. Any info or ideas would be great...