PDA

View Full Version : Coolant temperature below 90



paul.decowski
01-08-2007, 06:47 PM
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
01-08-2007, 06:55 PM
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
01-08-2007, 07:06 PM
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
01-08-2007, 07:17 PM
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
01-08-2007, 07:44 PM
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
01-08-2007, 07:54 PM
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
01-08-2007, 07:57 PM
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
01-08-2007, 08:00 PM
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
04-08-2007, 12:39 AM
i would try a thermostat first be4 going any further:D:D:D 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
04-08-2007, 09:20 AM
OK I had it plugged with VAG COM and it came up with one fault (fuel mixture, as the car does roundabout 13 MPG :aargh4:) 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?

cronic
15-01-2008, 01:35 PM
i would try a thermostat first be4 going any further:D:D:D 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


i think i have the same issue also...temp sensor for water reading low and the oil temp never really gets above 65-70° + fan is running constantly...!

Eshrules
15-01-2008, 01:45 PM
OK I had it plugged with VAG COM and it came up with one fault (fuel mixture, as the car does roundabout 13 MPG :aargh4:) 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?

i'd be tempted to go at this the reverse way round, the temp sender first, then the thermostat. i think it's highly unlikely it'll be the stat if you're finding no issues with the engine running constantly cold/warm, if it's simply a dash reading fault, its more than likely going to be the temp sender, a very well known fault througout the range and an easy part to replace.