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Antifreeze Reservoir Tank Pressure Relief Valve

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After a recent water pump replacement on my 1999 996, I filled the resovoir with 50/50 antifreeze as per instructions. The plastic high pressure releif valve keeps lifting indicating very high pressure in the tank. I believe that I may still have air in the system and that's why the valve extends upward after driving the car a few miles. This valve never lifted prior to the water pump R & R. Also, temperature at a red light creeps up to the middle of the zero at the "180" mark with A/C on. What is the normal operating temperature? Also, what is the correct procedure to purge the air out of the cooling system?



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As Loren said Filling with a vacuum filler is the correct way to fill.

If you have a lot of air you could damage the engine by driving, it can cause steam pockets/hot spots in the head.

That said sometimes you can purge the system by lifting the bail (snap it vertical) on the pressure relief valve when the car is cold and there is a vacuum in the system. This will often pull the AF out of the reservoir so you will need to refill it each time.

You will probably need to repeat this a couple of times to get most/all of the air out.

The needle creeping to the center of the "0" is not excessively hot., mine runs between the "8 & 0". On a hot day in stop and go traffic with the air on it will run on the "0"

The system is pressurized when hot, 1 bar-14.4 lbs, the valve lifting is normal operation.

Edited by fpb111
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The pressure relief valve act normal, when hot: valve on full lift, when cold: valve down. The valve will remain down (with hot engine) if the pressure cap is leaking or in case of a relatively large leak elsewhere.

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