Temperature Gauge Not Stable
10-23-2007, 11:46 PM
#1
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Temperature Gauge Not Stable
The temp gauge on my 1998 A6 1.8T (UK model) no longer seems to be working properly.
It always used to be rock solid at 90 deg, now it generally sits below this at about 75 deg, and sometimes drops down to zero whilst driving.
I've read it might be a faulty coolant sensor. Does this sensor only affect the gauge reading? Or does it control the car's cooling as well?
The car isn't overheating and the fan seems to cut in OK.
Is this something I should get fixed ASAP? Anyone know what a dealer would charge to do it?
It always used to be rock solid at 90 deg, now it generally sits below this at about 75 deg, and sometimes drops down to zero whilst driving.
I've read it might be a faulty coolant sensor. Does this sensor only affect the gauge reading? Or does it control the car's cooling as well?
The car isn't overheating and the fan seems to cut in OK.
Is this something I should get fixed ASAP? Anyone know what a dealer would charge to do it?
10-24-2007, 04:31 AM
#4
Thermostat? Not "obvious" to me at all. Especially given the high failure rate of the temp sensors
Start cheap and simple!
The sensor is less than $20 and takes half an hour to replace.
The sensor is less than $20 and takes half an hour to replace.
10-24-2007, 05:15 AM
#6
Yep, besides, even with a bad thermostat, it will eventually heat up...
only in freezing weather will it drop a lot, and I've never seen one drop to zero...
But I have seen a faulty sensor cause it to drop to zero...
But I have seen a faulty sensor cause it to drop to zero...
10-24-2007, 05:20 AM
#7
LOL
There does tend to be some confusion about the difference between overheating and boiling over. It is possible to have one without the other.
A car can be overheating without actually boiling over (eventually it will probably overheat to the point where it does boil over though). It can also boil over without overheating (headgasket leak, etc)
A car can be overheating without actually boiling over (eventually it will probably overheat to the point where it does boil over though). It can also boil over without overheating (headgasket leak, etc)
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10-24-2007, 05:44 AM
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Not at all true!
Under normal operating conditions, a motor will not eventually heat up with a thermostat stuck open. The water will constantly flow at maximum capacity, lose heat int he exchanger, and overall run cool. This is bad. Tis is why we have thermostats in the first place.
For a cooling system to work, it must have excess cooling capacity under all normal operating conditions and temperatures. A thermostat can ONLY reduce cooling by blocking water flow from the motor to the heat exchanger (radiator).
If this were not true the car would overheat regularly. Think about it.
If it is running cool, and then runs cooler still with air flowing through it, i would first suspect a thermostat stuck OPEN (not closed, as most are probably more familiar with).
So could it be a lot of things? Sure. But if it consistently acts as a open thermostat would, that is what I suspect first.
Grant
For a cooling system to work, it must have excess cooling capacity under all normal operating conditions and temperatures. A thermostat can ONLY reduce cooling by blocking water flow from the motor to the heat exchanger (radiator).
If this were not true the car would overheat regularly. Think about it.
If it is running cool, and then runs cooler still with air flowing through it, i would first suspect a thermostat stuck OPEN (not closed, as most are probably more familiar with).
So could it be a lot of things? Sure. But if it consistently acts as a open thermostat would, that is what I suspect first.
Grant