Engine overheat fix with coolant pressure release... but WHY? - Alfa Romeo Forum
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Engine overheat fix with coolant pressure release... but WHY?

Hi Forum

Help!! I had a 2003 Alfa 156 jts and a weird scene just happen. Wonder if this also happen to other 156 owners

I was having overheat message on the dash warning when i am in a traffic with my air conditioner on after a intense day of driving. So I pull over and put on my signal light.

Pop the hood and check everything; no signs of water leak, no signs of fan stop, coolant level seems to be down a bit.

So I starts to open the coolant tank slowly..intend to put some water in. But when i turn a bit, sizzling sounds comes up (which kinda normal). but suddenly clear coolant water seems to pour back in rapidly and seems to almost overfill the tank. So I turn it back tight again and level go down a bit.

I repeat this motion a few time until the pressure of the coolant is completely neturalize to open and I check the coolant now is back to the normal level.

I go back to turn my engine on and the coolant seems to be back to the normal and even a bit lower. My overheat problem seems to be fix with me depressurize the coolant system.

But WHY? Does anyone have this experience before? What is the common problem that cause this and why the depressurize fix the issue?

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Water boils at a higher temperature when it is under pressure. When you release the pressure, the water will boil, expand and turn to steam........
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There is an airlock in the coolant system.
Get the car up to temperature while standing so that the cooling radiator fan kicks in twice. Remove the filler cap slowly as before and leave it off. Top up the coolant to the correct level.
Leaving the car ticking over, proceed to the next step.
Look at the left hand headlight side of the engine bay as you are standing in front of the car.

There is a plastic flat head screw at the top left side of the radiator. This is the bleed screw...
Undo it slowly until you see coolant leaking continously from the radiator without any hesitation, it should be a nice steady flow.
It should take quite a few full turns of the bleed screw to see the coolant start to appear but dont remove the plastic screw completely, just be patient. Once you have a nice steady flow, retighten up the plastic bleed screw up and top up the lost coolant again. Let it tick over until the radiator fan kicks into action yet again and replace the filler cap. Job done.

Just be mindful of the temperature gauge. It should reach just below 90 while moving after at most 5-6 miles (8-10Km) of normal driving and go slightly above 90 when sitting in traffic... If it doesnt do any of these and sits at a lower temperature than that, your thermostat is siezed and needs replacing as soon as possible. That will be the initial reason why it overheated and let air in the system

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coolant , engine , fix , overheat , pressure , release

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