Expansion tank cap

tom1979 · Nov 19, 2018

does anyone know a good way to test the expansion tank cap vent on a D2?

I recently pressurised my system looking for leaks (found plenty) but I’m sure it’s not meant to hold 30psi in the system!! The cap I have got is a new genuine one but, like the old one, tight to do up

sierrafery · Nov 19, 2018

I can't see a way to test that other than removing the tank, empty it and pressurise it through the bottom outlet port, then the valve should open at 1.4 bar ... be aware that the cap must be tightened to maximum possible otherwise the bottom oring is blocking the overflow hole on the tank where the excess of pressure should leave the system

if you presurised the system through that yellow hose the valve doesnt work cos the pressure goes through it

tom1979 · Nov 19, 2018

sierrafery said:
I can't see a way to test that other than removing the tank, empty it and pressurise it through the bottom outlet port, then the valve should open at 1.4 bar ... be aware that the cap must be tightened to maximum possible otherwise the bottom oring is blocking the overflow hole on the tank where the excess of pressure should leave the system

if you presurised the system through that yellow hose the valve doesnt work cos the pressure goes through it

Ok thanks. no I pressurised it through the right hand hose with the shrader valve on, the yellow hose was blanked off. I didn't block the overflow though, so maybe there is something wrong with the cap as I thought it vented through the overflow not the return from the radiator (where I have my yellow hose blanked off)

sierrafery · Nov 19, 2018

You can buy genuine BMW cap cheaper than the LR one and it's perfect fit https://www.ebay.co.uk/itm/Genuine-...526572?hash=item211ba2102c:g:-5UAAOSwo4pYQDUJ

Expansion tank cap

tom1979

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sierrafery

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tom1979

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sierrafery

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