Oil/Coolant Temp - Not reaching operating temp

[abaird]

Hello,

I just replaced my water pump assembly, thermostat, and CTS, before the pump failed my oil and coolant temps were normally around 210°-230°f. Now they won't get above 185°-190° no matter how long it's running for, and it takes longer to warm up, is this normal? I've bled/burped the cooling system several times from the top of the system from the heater core hose. I've scanned it and it shoots no fault codes, and the radiator fans are not running all the time, could the new thermostat be bad? Could the CTS be bad?

[MetalMan]

Which thermostat went in? Generally speaking, the thermostat is responsible for coolant temperature (assuming there are no cooling limitations, i.e. clogged radiator). Usually air in the system would cause high temperature, not low (because of reduced system functionality), so this is why thermostat is my guess.

On the flip side I don't know what is a normal temp for these engines. One thought is that with these new components your cooling system is working better. now.. whereas maybe before it wasn't working as well, and now the temp doesn't go as high / as quickly.

[Smac770]

After changing the coolant along with the coolant pump/thermostat/temp sensor, I noticed it seemed to take a bit longer to come up to temp, maybe an extra mile or two vs before. But I don't notice it so much now, 3 months later.

The thermostat doesn't even open until 95°C (203°F), and unless you're smashing it hard, it tends to sit right around that point. That it was normally "210-230", that's way high, and it should never really go over 105°C (221°F), when the thermostat is full open and the fans kick in. Maybe the system is just working better now. But at the same time, 85°-88°C would seem below "normal", which I'd expect to see in the mid 90s°C. Is it possible the thermostat is bleeding a bit of flow when it should be closed? Is the temp sensor not quite spot on calibration? Who knows. But it's not like it's "completely not in the game"; I'd run with it unless you have a return window you're contemplating or such.

[Theiceman]

i dont know how much truth to assign to this , bu i once read that they dont read actual temperature anymore .. now when the ECU sees the temp rising to a certain temp it just sets the the guage to mid point. As it was creating too many calls unde waranty for overly concerned customers. has anyone else heard this ?

As my car is in Celsius it is hard to compare as i don't know the US gauge layout. but mine goes to 90 and jut sits right there and never moves after a few minutes. I find it more helpful to watch the oil temps if you have that enabled, that's all that really matters anyway.

[Smac770]

That's only for the coolant temp display at the instrument cluster. And that's how Audi operates it in B8 (there's not even a coolant temp gauge in B9.5). But that's only for the display gauge. The actual operation of the car is done per the coolant temp sensor reading.

[abaird]

So is it most likely that the CTS is faulty?

[Theiceman]

That's only for the coolant temp display at the instrument cluster. And that's how Audi operates it in B8 (there's not even a coolant temp gauge in B9.5). But that's only for the display gauge. The actual operation of the car is done per the coolant temp sensor reading.

yes ,, im assuming he is getting his temp readings from the display on the IC ,., but maybe not ?

[abaird]

yes ,, im assuming he is getting his temp readings from the display on the IC ,., but maybe not ?

Im getting the data from an OBD2 scanner

[Smac770]

You'd have to specifically test the temp sensor to conclude it's off. But that the sensor is a simple potentiometer, it could just as easily be something in the wiring or even in the ECM circuit itself. From the table, we see more resistance is a lower temp. So if there's any corrosion or poor connection adding a little extra resistance, ....

ECT Temperature vs Resistance
Temp (C) min value ohms max value ohms
- 40 36816 43714
- 35 28840 33978
- 25 17680 20530
- 15 10940 12534
- 5 6897 7804
0 5535 6226
5 4443 4970
15 2923 3235
25 1978 2167
35 1369 1486
45 965 1039
55 692 738
65 503 533
75 372 392
85 279 292
95 213 223
105 164 172
115 127 134
125 99 106
135 78 84

[Theiceman]

ive never checked mine from OBD stream , i will check it next time out to provide some comparative data .. I imagine your gauge goes to where it should though right ??

Im wondering if your questions are exactly why Audi did that .... lol

[Smac770]

Audi already said as much. Owners weren't capable of just letting the coolant temp do its thing without getting all concerned, so Audi just said f it', once it's 75°C, and as long as it's not over 105°C, it'll just park in the middle of the gauge. This was at the start of B8, if not earlier.

Anyone trying to use the instrument cluster gauge to assess the actual coolant temp is doing it poorly. The only thing the gauge is going to tell you is "it's too cold, it's too hot, it's just right".

[Theiceman]

Audi already said as much. Owners weren't capable of just letting the coolant temp do its thing without getting all concerned, so Audi just said f it', once it's 75°C, and as long as it's not over 105°C, it'll just park in the middle of the gauge. This was at the start of B8, if not earlier.

Anyone trying to use the instrument cluster gauge to assess the actual coolant temp is doing it poorly. The only thing the gauge is going to tell you is "it's too cold, it's too hot, it's just right".

the "goldilocks" gauge..