4200 GT issues with over heating

ps1

ps1

Junior Member
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Hi all,

I’ve been enjoying my '06 4200 GT all summer, but over the past couple of months I’ve developed an issue with engine temperature management.

Previously, the temperature gauge never exceeded 90°C under any driving conditions. Recently, however, after only a few miles of urban driving — even at low ambient temperatures — the gauge rises above 90°C and intermittently fluctuates/flickers.

When the car is idling, the cooling fans engage, bringing the temperature down, but the cycle then repeats as soon as the temperature climbs again. The fans are running at high speed, creating significant vibration through the chassis and excessive noise, which I have never experienced prior to this issue.

I’ve had it inspected by my mechanic, who advised that because the fans are activating and reducing the temperature, he isn’t concerned. However, the behaviour is clearly abnormal, and I’m not convinced this is operating as intended.

My initial suspicion is a faulty coolant temperature sensor, temperature gauge issue, or a possible ECU misread. Also the fans may be about to die due to the noise and vibration they make. I wanted to check if anyone else has encountered similar symptoms before I start replacing parts unnecessarily.

Any insight would be appreciated and apologies if I have posted in wrong place.
 
It's quite normal for the temperature to rise above 90 degrees.
Infact I'd say it is not normal to be running below 90 all the time, stationary in traffic it should rise above.
However, I take the temperature from my ultragauge plugged into the OBD port.
Stood in traffic, quite normal for the temperature to rise to above 95, fans cut in, it drops to low 90's.
I assume you have experienced the fans cutting in before when stationary?
They shouldn't make unnecessary noise and vibration.
I'd hook something up to the OBD port to live read the temperature and compare to your dash temperature gauge first, the dash temperature gauge is more of an approx indication!
 
Do the fans run at low speed or straight to high?
If straight to high then the fan resistor is dead but a cheap part to replace.
When I first bought my Gs the fan resistor had failed and there was a relatively decent amount of noise / vibration when they cut in straight to high speed.
Also if it’s original replacing the thermostat is a good idea.
 
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If your fans are vibrating it might be because there's an imbalance. That usually happens when then fan blades are dirty because of oil and dirt projections. It might be a good idea to clean the fans before the vibrations starts damaging them.

As for the overheating there are lots of possible causes, so it's not easy to diagnose:
-Low level of coolant/old coolant
-Head gasket (but usually you should be able to see gas escaping from the coolant tank
-Defective coolant tank cap or not well tightened (quite likely)
-Small holes in the coolant tank
-Clog in the radiator or somewhere in the cooling circuit, or very dirty radiator
-Defective thermostat valve that opens at an temperature higher than it was rated for (that would be my guess)
 
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Check live data every time using diagnostic gear and I certainly recommend changing the thermostat as it's going to be over 20 years old unless you know it's been done in the service history.
 
Just checking though if the fans when they go on should be vibrating so much? They make the whole car vibrate!
 
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