Right after replacing my power steering lines which I recently posted about and test driving for about 30 minutes, the coolant expansion tank decides to rupture just as I get back onto my driveway. At least I think it was only the tank, since there doesn't seem to be coolant leaking from anywhere else. Is there anything to look for to make sure it's just from the age of the original expansion tank, and not another problem causing overpressurization in the system? It looks like the tank is completely empty, so I was going to just start the motor for a few minutes to see if coolant drips from anywhere else besides the tank.
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No point to run the engine again to check for cooling leaking with a ruptured tank, as there’s little pressure to force the leak.
I would replace the tank, fill up coolant, close cap and drive around the block to get temperature to around 60c then shut down. Slowly open the cap to let the air out then close it. Drive to operating temperature and then squeeze the upper hose to see if it’s very hard or not. If it’s hard then combustion leaking into coolant.
This is one way to run the stock parts at lower pressure than the 2.0 bar / 29psi spec, if the engine doesn’t run hot normally. -
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My main concern is installing a new tank and having it burst because the system is over pressurizing for some reason. Maybe I’m thinking too much?Originally posted by sapote View PostComment
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Also, shouldn’t there be a high pressure release (in the cap or elsewhere) that should have vented the pressure to prevent the tank from being damaged?Comment
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Yes, even a used one will work if you want to test. These tanks are pretty durable.Originally posted by FFWD View PostComment
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Yes the cap would release the pressurized GAS at 29psi but this is high enough to bust an old tank.Originally posted by FFWD View Post
If combustion gas enter the coolant in the head then the cap release valve won’t be able to save you as it can’t release lLIQUID coolant fast enough.Comment
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A lot of people run a lower pressure cap on the expansion tank, so instead of venting at 2.0 BAR, it would vent at 1.2 or 1.4 BAR. I went with the 1.2 BAR cap from German Auto Solutions when I redid my cooling system recently, I'm pretty sure there's a BMW part that works as well. It doesn't fix any overheating issues, but the idea is that it helps save an older expansion tank or radiator if overheating does occur.
Had you checked the coolant level recently or perhaps added any coolant? Apparently they also go boom if they're overfilled, as you loose the air pocket for the fluid to expand and it has no place to go when it heats up.Comment
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If the engine is not operating higher than 110c then no reason to use the 2bar cap.
50% mix coolant will boil above 120C at 10psi.
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2004 Dinan S3-R M3
2023 X3M CompetitionComment
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