Coolant temperature below 90

[paul.decowski]

Hello everyone,

I noticed that the coolant temperature gauge shows low temperatures when driving fast (e.g. motorway). Fair enough, understandable that air flow cools down the water in the radiator but isn't thermostat to block water flow into engine block when temperature drops below 90?

The reason I'm asking is I spoke to a mechanic and he said it's OK until it doesn't go above 90 but i thought that thermostat should keep the optimum coolant temperature which is just above 90.

Is it OK if the temperature in such driving conditions drops to about 70?

Thanks,
Paul

[Col]

It's ok as in it won't cause any damage.

However the sensors are notorius for failure so that could be your problem (you didn't state what age / engine your car is by the way?).

Also does it take a long time to reach normal temperature, is the fan on all the time?

My guesses are in order of likelyhood;

Coolant temp sensor

Thermostate stuck open

Cooling fan always on.

[paul.decowski]

Thanks for quick reply.

The car is 1.8i 1995.

So you're saying it won't do any damage but it IS a fault (i.e. is not normal) ?

Temperature reaches 90 after a few miles in town driving. I'm not sure about the fans, one of them goes off after a while when I stop the engine and the other one runs all the time (it runs quite slow and wobbly but I hope it's not a serious issue, well the engine doesn't overheat so I don't think so).

As to the faults you mentioned that's what I thought before I spoke to the mechanic, but he said it's normal so I don't know if I should trust him now?

Is he plain wrong? Should I be looking for another one?

Regards,
Paul

[RickT]

Thanks for quick reply.

The car is 1.8i 1995.

So you're saying it won't do any damage but it IS a fault (i.e. is not normal) ?

Temperature reaches 90 after a few miles in town driving. I'm not sure about the fans, one of them goes off after a while when I stop the engine and the other one runs all the time (it runs quite slow and wobbly but I hope it's not a serious issue, well the engine doesn't overheat so I don't think so).

As to the faults you mentioned that's what I thought before I spoke to the mechanic, but he said it's normal so I don't know if I should trust him now?

Is he plain wrong? Should I be looking for another one?

Regards,
Paul

Its not noramal for the temp gauge to drop when on the motorway.. its could be a temp sensor which keeps the gauge stable at 90'c... ie... if you pull the car into VAG-COM and monitor the temp on idle i have seen mine go up to 100'c and the gauge will not move, and also seen it at 81'c when the gauge shows 90'c, if there was not a resistor in place the gauge would bounch around all over the place...

I would rule out the thermosat stuck open/closed as i had that issue the the gauge did not move, just stopped warm air into the cabin.

I would be thinking more of a sensor issue.. i will do some digging to see what i can find out..

RickT

[paul.decowski]

That would be much appreciated as I'm happy to do the dirty job myself rather than paying some "mechanic".

Having said that, what are rough prices for a new thermostat and temperature sensor?

Cheers,
Paul

[RickT]

That would be much appreciated as I'm happy to do the dirty job myself rather than paying some "mechanic".

Having said that, what are rough prices for a new thermostat and temperature sensor?

Cheers,
Paul

Thermosat (full unit) cost me £30 from Audi (parts desk), temp sensors are about £15 as they are pretty common..

I would suggest getting it onto VAG-COM as all faults should be reported in there.

RickT

[Frenchman]

I just changed the coolant temp sensor on my 2.8 and it cost £28 from Audi, took me about 45 mins, access was a bit tight but it's easier on some of the other engines 10 minute job.

What happened with mine is would get up to about half way then if I turned the engine off for 5 mins and restarted it would just sit there on cold, and other times just behave strange, anyway the coolant sensor fixed it.

Frenchman

[paul.decowski]

I'm having it VAG-COMmed tomorrow (by the same mechanic unfortunately) so might get some more details.

On the other hand the car hasn't got any service history so there may be plenty faults which have been fixed but not reset which may lead to confusion. Anyway I hope it will give us some idea about where the problem lays.

Thanks,
Paul

[stubbsy]

i would try a thermostat first be4 going any further i had same probs as yourself,would never read over 75/80 water and 65 70 oil, changed thermostat and hey presto both gauges reading as they should

[paul.decowski]

OK I had it plugged with VAG COM and it came up with one fault (fuel mixture, as the car does roundabout 13 MPG ) so no faults whatsoever about the cooling system.

I think I'm gonna replace the thermostate anyway. It looks like it's stuck open and lets cool water into the engine block even though the temperature is way below 90, on the other hand that would be hell lot of coincidence that the gauge is perfectly at 90 in town driving... Well, it's not expensive so I'm gonna do that and if it doesn't help I'll replace the temp sensor as well unless someone else is able to pinpoint the problem.

BTW: Where is thermostate in this model? Is it where the lower hose goes into radiator?