Collant temp indicator

[Paulwestbrook]

Happy New year to you all.
Question ~ The temperature needle keeps yoyoing whilst driving. I takes a long while to indicate the correct engine temp then randomly drops to just above zero, creaps up again and then back down. The coolant level is just below the markers when cool. There is no apparent performance drop or engine noise at any time. The in car temp also drops with the needle. Is this a thermostat on it way out?
Paul

[Phil]

Originally Posted by Paulwestbrook

Happy New year to you all.
Question ~ The temperature needle keeps yoyoing whilst driving. I takes a long while to indicate the correct engine temp then randomly drops to just above zero, creaps up again and then back down. The coolant level is just below the markers when cool. There is no apparent performance drop or engine noise at any time. The in car temp also drops with the needle. Is this a thermostat on it way out?
Paul

Hi, happy new year.. odd one, the thermostat could be stuck open, does it get cooler the faster you go?

[Paulwestbrook]

No, its totally random. I have noticed that if I stop for around 5 minutes for petrol etc, the needle will go straight to correct temp. Than as the journey continues, the movement starts again.

[Paulwestbrook]

I suppose Phil, your explanation is totally logical. As the water is cooled during the journey via the rad, then the indicator would drop as well as the in car temp. Does the thermostat open and close when engine temp is met. I always thought it would stay open once optimum temp is reached. It is odd though.

[Phil]

Hi, the thermostat will open once running temp is reached.
How long does it take to stablise? My first 75's temp gauge used to "dance" if I drove it, let it stand for half an hour to an hour then start it up, it would dance around as the temp sensor sensed water that had cooled more than some, as it mixed, it settled after about thirty seconds. The temp gauge doesn't follow logic on these cars. It is programmed to display what it does at various temperature ranges.

[Paulwestbrook]

It takes a good twenty minutes to get to where it should be, this lasts for about 5 minutes and then it drops right down, creeps up and so on. What about the sensor, could the problem possible lie there?

[Phil]

Originally Posted by Paulwestbrook

It takes a good twenty minutes to get to where it should be, this lasts for about 5 minutes and then it drops right down, creeps up and so on. What about the sensor, could the problem possible lie there?

I would say yes, but you say the heater goes cold so I think not. Do you have any coolant loss? What does the coolant look like? Is it a nice clear pink/orange colour?

[T-Cut]

Originally Posted by Paulwestbrook

The temperature needle keeps yoyoing whilst driving. I takes a long while to indicate the correct engine temp then randomly drops to just above zero, creeps up again and then back down.

This is not normal in a 1.8 engine, which should pretty quickly reach 'normal' running temperature and stay there, whatever the driving conditions or outside temperature. Having said that the gauge is quite useless for telling you what the temperature is actually doing. Far better to monitor it using the OBD screen. There's info on this if you need it.

The yo-yo temperature gauge could be a reflection of an actual variation. If so, then there's a fault in the cooling system somewhere. First suspect is the thermostat, which will be the in-line Pressure Relief type in a 2004 model. These however, usually perform well.

Second suspect is the temperature sensor mounted at the right end of the head as you look at the engine. If that or the connection is faulty, the gauge will misbehave. Does the cooling fan ever trip on unexpectedly?

Are you absolutely sure the coolant inventory is right? The level may seem OK, but an air bubble in the system could cause erratic gauge activity. Do you check it regularly and do you have to top it up very often?

TC

[Phil]

Originally Posted by T-Cut

This is not normal in a 1.8 engine, which should pretty quickly reach 'normal' running temperature and stay there, whatever the driving conditions or outside temperature. Having said that the gauge is quite useless for telling you what the temperature is actually doing. Far better to monitor it using the OBD screen. There's info on this if you need it.

The yo-yo temperature gauge could be a reflection of an actual variation. If so, then there's a fault in the cooling system somewhere. First suspect is the thermostat, which will be the in-line Pressure Relief type in a 2004 model. These however, usually perform well.

Second suspect is the temperature sensor mounted at the right end of the head as you look at the engine. If that or the connection is faulty, the gauge will misbehave. Does the cooling fan ever trip on unexpectedly?

Are you absolutely sure the coolant inventory is right? The level may seem OK, but an air bubble in the system could cause erratic gauge activity. Do you check it regularly and do you have to top it up very often?

TC

Hi TC, all 1.8T's have PRTS.

[Paulwestbrook]

Phil . The coolant level is fine and 'clean' pink.

T-cut. I have had a coolant loss problem, it turned out to be a split T piece on the hoses at the top of the rad. Its been fine since. Interesting what you say about the fan. Just realised it doesn't come on anymore when I stop driving. It used to all the time for about 3 minutes once the engine was off. Is the fan linked into the sensor as well?