Hi guys,
I have just purchased a 1999 A4 (https://www.audiforums.com/forum/sho...22#post1110722) and notice that both the coolant temp and oil temp don't really seem to rise as they should after the engine has warmed up.
If there is not much airflow (ie: slow driving / idling/ in traffic etc) the coolant probably sits just below 90, but then once you speed up and get airflow again it goes below 70.

As for the oil temperature, the needle sits very much to the left of the dial, though I think the gauge works because it rises a little bit (but no where near as much as the coolant gauge) again when there's no airflow.

I'm guessing the above is NOT normal since once the car is warmed up both gauges should sit within the middle of their range???

Perhaps a I need a new thermostat?? or maybe the sensors / temperature gauges are playing tricks... Any advice would be much appreciated!
Cheers,
Rick.

 

how could you know the coolant temp? maybe yours is different but mine is a range of hot through cold.
as for the oil, what line is it on? if it doesnt register at all could be a sensor, but it sounds like it shows something. what?
a thermostat sounds likely for the coolant, but even running with no tstat your coolant will eventually warm up some. i would rule out a gauge problem since they seem to be working, even thought not showing supposed correct readings

 

Sensors are notorious for petering out over time. My coolant gauge likes to be schizophrenic in the winter and the consensus is a buggered coolant temp sensor, I just haven't had the motivation to replace it yet (it's not in a very convenient location on my engine...) so there is a very high possibility your sensors are in need of replacement.

As for the oil tho (not sure how your gauge looks) mine has never gotten to half of its value after warming up (unless I'm cruising up a steep canyon, then it gets close) but it always hangs out about a quarter of the gauge- half way between far left and straight up. Do you mean yours barely moves at all from the far left or does it raise to the marker between the aforementioned two points?

 

Same here... far left is 60c, middle is 130c... mine hangs out about 1/4 the way up at ~100c. And, since the thermostat is rated at ~90c and oil is suppose to be slightly warmer than that, all's good.

 

Thank you all for your replies!
To save any confusion I have taken the liberty of posting a dash photo for all to admire. It seems for most of you, it will feel just like home


The coolant needle will rise (eventually) to 70-80 with slow driving, but if you go on a freeway or something where there's lots of airflow it will go down again. Oil temp stays between 60 and 70, so pretty much to the left of the gauge. I would have thought the oil temp would be a bit higher.. so it must be a sensor thing.

In saying the above I've only driven a couple of times, never on a demanding road, but a good 30 minute trip and saw the symptoms above. I'm pretty easy with the throttle too, (though like to go quick around the corners).

Potentially if the thermo is not letting it get to temp... is that a bad thing as the engine is always "running cold" ??? or does it not matter, as long as it doesnt get too hot (which obviously isn't the case here)

Thanks again heaps for your comments and help.
Rick.

 

Ahh.. yours should be hanging out in the middle

I would think it's most likely a thermostat or maybe your fans are running on HIGH constantly..? If you turn on the a/c and load the engine (hills, dragging brakes, spiritedd riving, etc) can you get it to go up?

 

Thermostat is bad. When they go bad they pop open and stay open. This means the coolant does not stay in the motor long enough to warm up, temps will come up slightly when the car is sitting perfectly still because the coolant does not cool down as it flows thru the radiator because of of the lack of air flow over the radiator when sitting still.

The cool coolant effects the oil temps since they both flow thru the coolant/oil exchanger.

What your seeing is exactly what I saw when driving my car without a thermostat at all.


Allowing the coolant to stay too cool is a bad thing because this means your ECU is still in the "choke" mod running the engine rich, it does not switch to the normal tuning till the coolant reaches over 80 degs.

 

The coolant temp sensor cost me $7 at oreillys and took under 10 minutes to change. Apparently with a bad temp sensor the car stays in warm-up mode, and you dont get quite the same power or response. After changing mine I didnt notice much of a difference at first, I think its somewhat adaptive.

 

But that wouldn't cause the oil temps to be very low since the coolant temps will be up where they should but just show low on the gauge.

 

is it possible for a thermostat to stay closed? I'm having the opposite problem i'm overheating and i don't want to hear that its my water pump lol