P38 overflow bottle cap Repair

[peter51]

The washer on the Cap hardens fairly quickly inside 2 years on aftermarket versions. I noticed that the system wasnt holding the usual 0.6 bar via a pressure guage I have fitted to the cooling system. I have a cooling system pressure guage permantly plumbed into the line to the throtle body. If you do boat towing etc then accurate pressure is an essential parameter to monitor in older vehicles. Low, nil or high pressure in the cooling system is good to know in my opinion.

This washer can be replaced with a nitrile oring size AS 568-214. It seals the sytem really well as long as you dont over tighten the cap to tear the oring.

The picture shows the original washer and the oring.

Much cheaper than a new cap.

If you decide to renew the cap - keep the old one and fit a schrader valve to test your cooling system - especially after engine work. E.G after a cam change and before start and 20 minute run in, you should pressurize the cooling system to check for leaks. Therefore you will not have the misfortune of having to shutdown within the first 5 minutes of the breakin.

[peter51]

I added a picture of the oring in place. It is at the base of the stem in place of the washer.
You will also notice 2 new brown VITON orings on the stem of the cap. With the original flat rubber washer in place, the cap still didnt hold pressure with these 2 slightly oversize orings in place. I took the bottle off, sealed up the outlets, pressurized it to 5 psi and sure enough air was leaking from the flat washer - by screwing it down hard I could reduce the leak but it still came from the same point. I then fitted an oring instead of the flat rubber washer as an experiment and i was delighted to see only the odd bubble appear at the same pressure.

Once back on the car the system now holds pressure for quite a while after shutdown.

[TheTree]

Hi,

I just bought a spare cap from the UK for the princely sum of about 4 quid :cool:

But this is good to know !

Steve