Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Mystery coolant loss

I've had my 1983 +8 since 1988, it has always blown the coolant out of the expansion tank i.e. I fill the system to the marked level go for a spin and the coolant has gone!
It's happy to run like that all the time, no further loss when I look at the level in the radiator
There are no puddles in the garage. no anti freeze stains in the engine bay or around the expansion tank
I've run it up to temperature in the garage when topped up and the coolant doesn't appear to be lost, level doesn't change and no puddle.

It's had a new engine and radiator (a rebuild not diagnosis by changing parts!) some years ago.
I've changed both radiator and pressure caps (melvyn R suggested a higher pressure one)
The mystery fluid loss was unchanged.
The only constant is the expansion tank itself, but it looks ok with no splits
I assume the coolant is going out through the overflow pipe when driving

Any thoughts welcome

Hi there

Please remember that your expansion tank was not made by Morgan motor company it’s a bought in item and the markings on it will relate to the position in terms of height above coolant level that the original manufacturer of the model it was taken from decided. It has nothing whatsoever to do with the installation in a Morgan the markings are therefore irrelevant.

When the system burps out the excess water that’s the correct level for your installation and as long as you don’t lose fluid below this level anything above it will be blown out as you’re experiencing.

Hope that helps.

BR
Colin

Thanks Colin, I never thought of that & my Roadster will never hold fluid to the max line.

Interesting one about coolant fluid as my Mog has a silly habit of dumping it somewhere I know not where exactly and after a few months the low coolant light flicks on and off which is a little scary when far from home. Need to get KH to have a look !

Neither would my 2002 +8, I was having a good look and that’s when the penny dropped it was a LR header tank. One of my first meets with Peter Mulberry of Mulfab ended up with one of his header tanks and problem of loosing half the water from the OE was gone.

BR
Colin

I have the same issue with my 04 +8 and have come to the conclusion that when the system is full to the mark the OE expansion tank is not big enough to hold all the expanding coolant. So some coolant is lost. When the coolant is cold and contracted the tank is empty. So I would be interested to know if the Mulfab tank has a larger volume to handle the full range of expansion.

Mine would, but you had to ensure the tank cap was on VERY, VERY tightly down, if not it used to mysteriously drop a few mm after each run, so I assume under pressure a tiny amount of unseen vapour was escaping via the rubber cap seal - it took months of experimenting to find it was something so simple