Pressure cap blow off!!

M

mcbutler

New member
Hi all,

Well, dragged the car out for a spin today, popped into town to get a pressie for Kat then over to a garden centre to pick up a plant for her. On the way back I smelt a distinct 'puff' of hot coolant!!.
'Someones got a water leak' I thought, seconds later a gong and orange low water lamp!!!
Only a mile from home so nursed her back, no red lights or overheat warnings, oil temp steady and hot air coming from heater vents (always a good way to check).
Pulled up and could see steam emanating from the front of the bonnet drivers side, opened bonnet and pressure cap is sat on top of the rocker cover!! and coolant boiling and hissing all over the place.
Topped her up, took 2 1/2 boiled kettles, ran the coolant prime process and now shes stood outside 'cooling down' so I can check the level cold.

So, whats the chance of that happeing I wonder, you might all want to check your coolant tank caps are clicked all the way on, nice and tight......
 
Hmm, very interesting.

Just today I replaced my cap by a new one, as the old one had several traces of broken material.

White/Blue traces of water blown out:
20220812_105820_cpr.jpg

Several broken parts, inner o-ring lost: :o
20220812_201309_cpr.jpg

Old cap on the left, new one on the right:
20220812_193040_cpr.jpg

Yes, 10 year old caps should be checked or better replaced in advance. I will put this as an additional task into my recommendations.



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Yeah i need to check my seals, no obvious marking on the top of the header tank though.
Thanks for taking the time to post the pics, i appreciate that :thumbsup:
 
Is a very common problem on E46's and i've replaced a few caps with newer better ones, and also changed bleed screws for brass ones. Obviously any older car needs the whole cooling system going through at some point.
 
In 70,000 miles, my engine's used between 4 and 5 litres of Comma Extream G48 coolant. The 'floating prong' is a clever level indicator and makes the coolant level easy to check. That said, I noticed from the beginning that the cap didn't close tight, but assumed it tightened as it heated. I've never tried it to find out because there have been no sign of leakage or excess use.

It is noticeable in your 2nd photo, RobbiZ4, that the prong isn't central and this corresponds to the white marks on the inside of the cap. Seating the prong centrally under the cap is a bit fiddly. Is it possible that, once upon a time, yours wasn't central, was caught between the O-ring and its rim and coolant escaped? Or something like that?

p.s. Presumably, you've drained the system of kettle water by now and re-filled it with an equivalent of G48, have you?
 
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