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MG MGB Technical - Heater valve leak

I have noticed the tell tale signs on my distributor vacuum advance module of a water leak from my heater valve. The size of the leak is very small at the moment and the area remains dry when shut down.

Can anyone tell me how quickly these leaks tend to develop ? If it is unlikely to get worse quickly I would like to continue to use the car for the next two weeks before fitting a replacement.
P Allen

Do not operate the heater valve! If you move it it will fail much sooner and more leakish. Lots of cars run for long periods with no problem despite seeping valves, how's your carma?
Last guy I ordered one for didn't come back to fit it for a couple of months, until the night he forgot and tried to get demist - was here the very next day!
You can help out by loosening the rad cap to the first notch, which relieves pressure but keeps the water in, so long as you do not get in a situation that requires the insurance of the higher temp boiling given by pressure.
It is possible to block off the valve and heater hoses to remove it from the system, but that is more work than changing it, so is reserved for long term poverty or wilderness rescue.

FRM
FR Millmore

I had a leak develop in the valve in 2002 that had no effect on running, both on a longish trip across Ireland or overnight and the next day back home. However the replacement for that started leaking a couple of months ago and in the garage for a week or two it flooded the distributor. You could experience either, or something else. The diaphragm is pulled one way when fully open, and pushed the other when closed. When left to take it's normal position it's about half-way, so in theory this position should tend to open the split the least. The splits are usually in the outer part of the diaphragm i.e. the heater side of the valve, so closing the valve will stop any leak from the head, but you would need to remove the heater hose from the outlet and plug that with something like a spark plug (insulator end) to stop the leak altogether. If you really want to be able to use the car until a planned replacement, then I'd be doing that.
PaulH Solihull

Thanks for the replies gents. Taking on board what you have said, I will chance my luck and hopefully carry out the planned replacement in a couple of weeks time. I will put a deflector in place as a temporary measure to deflect any water from the valve coming into contact with the distributor cap and also carry in the boot (trunk) some gasket material and a 1/2 inch drill so that I can isolate the heater circuit if necessary.

Thanks again

Phil
P Allen

I just replaced my leaking one with one on e-bay that is claiming to be built to eliminate the issues with the originals. It looks just like the original.

I will keep the group up to date on how it works.
Bruce Cunha

You might also check that the leak is not from the hose/valve connection. That would be a simpler fix.
Roger T

This thread was discussed between 02/07/2011 and 03/07/2011

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