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MG MGF Technical - expansion tank cap

What are the symptoms of a failed expansion tank cap?

I have a 96VVC with 60K, The temperature gauge is midway when the tank starts to boil and bubble over. I have check the rivet in the cap and it is very slightly off centre.

Does the cap always use its valve or is it only opened in extreme circumstances.

I don't wnat to go to the expense of a new HG if its just the cap.

The tank starts to bubble over after about 10mins of running.
Rich

Change the cap anyway - they're cheap.

If it still bubbles over then it's not the cap.

SF
Scarlet Fever

The wifes car did the same, Rover 214. Would boil over after 10-15 mins. Garage spent half a day looking at it, then changed the exp. cap. Never saw the problem again.
Richard

Its has a white dot on it which I think means its a newer improved one.
Rich

>>If it still bubbles over then it's not the cap.<<

Unfortunately, there are some duff new caps out there in circulation... Get the cap pressure tested, and replaced if not hold the pre-requisite 12psi pressure
Rob Bell

>12psi pressure<

I though it was 14..... Anyway, get it tested of easier still buy a new one 3.50 from MGR.

I had a symptom of boiling and rising level of coolant in the expansion tank a few months ago. Techspeed suggested it was probably the cap and duly tested it for me and bingo, the cap vented early at about 10-11 psi. With a new cap fitted the coolant doesn't boil and doesn't rise up the expansion tank.

Tim
tim woolcott

You're probably right Tim: I tried to check this before posting, but couldn't find the rating in any of the documentation I had here...

14psi it is :o)
Rob Bell

This thread was discussed on 03/09/2003

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