'83 engine, '87 924s, which expansion tank cap?

[jvandyke]

We have an '83 944 engine in an '87 924s car, I believe the expansion tank caps are different, not sure which one would be "correct" or if it even matters. It seems the current one is for the '87. We're having weirdness with coolant. Level seems to migrate, system pressurizes on start up, suspect HG but wonder why it isn't blowing off access since it seems above 13psi, just curious why they changed caps.

[thomasryan]

I may be mistaken but the early cars use a 100kPa cap and the later cars take the 150.

test what you buy. I just replaced a three year old behr cap that only held 75% of its value. (15 vs 22 psi)

[v2rocket_aka944]

thomas' values are right..but it doesnt really matter.
use the cap you can get your hands on if you need a new one...lol

if the cap is good and you're running temperature is enough to make the low-pressure capped system start to boil anyways you got bigger problems..

[thomasryan]

higher psi will keep the size of the nucleate boiling bubbles smaller around the coolant passage around the exhaust valve. same theory as water wetter stuff and making mashed potatoes.

just an observation, higher compression ratios have higher psi caps.

[v2rocket_aka944]

...so if i wanted to boil potatoes i should use the low pressure cap....

[thomasryan]

you would want the 150kPa cap for your mashed 'taters....cuts the cooking time in half.