Unstable temp gauge
Discussion
Hello All.
Bit of an unusual one. I have an Infiniti Q50 2.2d (Nissan electrics, Mercedes engine).
About 3 months ago I noticed that from start up when cold, the temp gauge on the dashboard will get almost up to normal running temp, but then drop back down to somewhere between a quarter and a third warm. This will generally go on until the car is what I would consider to be 100% up to running temp (but tonight took about 12 miles before it was stable). This usually happens on my journey home from work, which is mainly A Roads, with no sitting in traffic.
The car has been back to the dealer twice, with full diagnostics run - firstly the instrument cluster was changed as a faulty gauge was suspected, then a coolant temp sensor changed as readings showed it was slightly out of tolerance. Neither ‘repair’ has fixed the fault, so it’s now booked back in for a third time. Frustrating as you can probably understand.
Would anyone have any other ideas what could be causing this? I’ve been assured that the engine / car is running absolutely fine, but I need to be able to trust what the gauge is telling me.
Any ideas much appreciated.
Bit of an unusual one. I have an Infiniti Q50 2.2d (Nissan electrics, Mercedes engine).
About 3 months ago I noticed that from start up when cold, the temp gauge on the dashboard will get almost up to normal running temp, but then drop back down to somewhere between a quarter and a third warm. This will generally go on until the car is what I would consider to be 100% up to running temp (but tonight took about 12 miles before it was stable). This usually happens on my journey home from work, which is mainly A Roads, with no sitting in traffic.
The car has been back to the dealer twice, with full diagnostics run - firstly the instrument cluster was changed as a faulty gauge was suspected, then a coolant temp sensor changed as readings showed it was slightly out of tolerance. Neither ‘repair’ has fixed the fault, so it’s now booked back in for a third time. Frustrating as you can probably understand.
Would anyone have any other ideas what could be causing this? I’ve been assured that the engine / car is running absolutely fine, but I need to be able to trust what the gauge is telling me.
Any ideas much appreciated.
This seems to be more common nowadays because cooling systems are better at shutting off flow to the radiator when they are cold. As a result the radiator stays full of dead cold water until the engine is good and hot. Then the stat opens and shoves hot water into the radiator, displacing the cold water into the engine which causes the stat to close again. It can repeat several times until things settle down. Many cars use a temperature gauge which is very insensitive around the normal running temp and that hides this effect.
If the stat is slow acting or even sticking closed it can make the problem worse, but it can happen in a healthy engine too.
If the stat is slow acting or even sticking closed it can make the problem worse, but it can happen in a healthy engine too.
GreenV8S said:
This seems to be more common nowadays because cooling systems are better at shutting off flow to the radiator when they are cold. As a result the radiator stays full of dead cold water until the engine is good and hot. Then the stat opens and shoves hot water into the radiator, displacing the cold water into the engine which causes the stat to close again. It can repeat several times until things settle down. Many cars use a temperature gauge which is very insensitive around the normal running temp and that hides this effect.
If the stat is slow acting or even sticking closed it can make the problem worse, but it can happen in a healthy engine too.
My only concern here is that the car / gauge never used to do this, only started about 3 months ago. If they tell me its all perfectly normal, I guess I'll live with it!If the stat is slow acting or even sticking closed it can make the problem worse, but it can happen in a healthy engine too.
stevieturbo said:
nevermind the OEM gauge, what does a proper scan tool show the temperature doing ?
OEM dash gauges rarely reflect the actual temperature.
Appreciate this, and according to data coming off the car all is running ok - but issue as far as I see it is that up until 3 months ago it didn't do it, and I want to be able to trust the reading from the gauge, otherwise I cant be 100% sure that all is running fine under the bonnet. OEM dash gauges rarely reflect the actual temperature.
The Aardvark said:
stevieturbo said:
nevermind the OEM gauge, what does a proper scan tool show the temperature doing ?
OEM dash gauges rarely reflect the actual temperature.
Appreciate this, and according to data coming off the car all is running ok - but issue as far as I see it is that up until 3 months ago it didn't do it, and I want to be able to trust the reading from the gauge, otherwise I cant be 100% sure that all is running fine under the bonnet. OEM dash gauges rarely reflect the actual temperature.
The Aardvark said:
Appreciate this, and according to data coming off the car all is running ok - but issue as far as I see it is that up until 3 months ago it didn't do it, and I want to be able to trust the reading from the gauge, otherwise I cant be 100% sure that all is running fine under the bonnet.
OEM gauge is rarely a reflection of actual temperature. they're programmed to keep the driver happy under most circumstances, rather than reflect actual temperatures. So you can never "trust" the dash gauge.Get a proper scan tool and view temperature readings directly if you have any concerns, and take things from there. But the gauge behaviour you are describing is not normal either, but you need to know what the temperature is actually doing..or at least what the sensor is doing.
stevieturbo said:
The Aardvark said:
Appreciate this, and according to data coming off the car all is running ok - but issue as far as I see it is that up until 3 months ago it didn't do it, and I want to be able to trust the reading from the gauge, otherwise I cant be 100% sure that all is running fine under the bonnet.
OEM gauge is rarely a reflection of actual temperature. they're programmed to keep the driver happy under most circumstances, rather than reflect actual temperatures. So you can never "trust" the dash gauge.Get a proper scan tool and view temperature readings directly if you have any concerns, and take things from there. But the gauge behaviour you are describing is not normal either, but you need to know what the temperature is actually doing..or at least what the sensor is doing.
So question is what else within the cooling system would cause the gauge to give unstable readings?
Further diagnostics booked in for next week, but really wondered whether there was something obvious that's been missed, or something completely obscure that could be worth checking out.
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