Fluctuating temperature gauge - Alfa Romeo Forum
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Fluctuating temperature gauge

So we know that the temp gauge will rise to just over 90 then drops as the thermostat opens and colder coolant hits the sensor.
On mine this fluctuation happens two times in a row since some time ago. I speculate that the colder coolant is causing the thermostat to close again and when it gets up to temperature, to open again causing a second drop.

Anyone has the same thing occur? Just a note that the engine warms up fairly quickly and temperature is right after that so doesn't seem like a faulty thermostat.
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So we know that the temp gauge will rise to just over 90 then drops as the thermostat opens and colder coolant hits the sensor.
Not in my car....

Gentle rise up towards 90, which slows in it's approach until it settles rock steady on 90.. No fluctuations or bouncing about...

Bare in mind that the gauge on the dash is deliberately dampened in it's response... i.e. anywhere between 85-95 actual temperature will appear as 90 on the dash...

If your dash needle swings about, then your actual coolant temp is bouncing about 10-15 degrees!

Sounds like your thermostat is on it's way out if it's slamming open/closed instead of a gentle response.. Should self-regulate nice and smoothly idealy!

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The gauge is generally pretty unresponsive and provides poor data. If you read from the odb port the temp does rise and fall a little +/- 5oC but my gauge generally stays solid but reads a little lower than it should. Sounds like your thermostat is working but take readings via the odb to check. Mine settles at 87 on a dual carriage way but the gauge reads lower. Only get 90plus if sat in traffic for along time. The fan is rarely needed. Turning the heater on also obviously makes a difference.
I have an infrared thermometer which is quite good to use for observing the heat transfer through the cooling system.
Edit: Having read editors response maybe my thermostat isn't at it's best either!
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Originally Posted by _The_Editor_ View Post
Not in my car....

Gentle rise up towards 90, which slows in it's approach until it settles rock steady on 90.. No fluctuations or bouncing about...

......
But you have a gt, which reacts completely differently compared to 156.
On the 156, the guage has a seperate temp sensor, and displays realtime. On the gt and 147, there is a single temp sensor for the ecu, which then sends the temp to guage via CAN. In this case it processes the temp, temperatures between 80 and 100 degrees C are always displayed as 90 degrees on the guage, so you won't see fluctuations between 80 and 100 .....
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But you have a gt, which reacts completely differently compared to 156.
On the 156, the guage has a seperate temp sensor, and displays realtime. On the gt and 147, there is a single temp sensor for the ecu, which then sends the temp to guage via CAN. In this case it processes the temp, temperatures between 80 and 100 degrees C are always displayed as 90 degrees on the guage, so you won't see fluctuations between 80 and 100 .....
Ah fair enough!

I assumed they'd be the same, I guess not..

Carry on everyone, nothing to see here
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