Coolant level

[Chilliman]

Last run before I tucked her up week before last (offshore again) I checked the coolant level before firing her up, and as I unscrewed the top of the expansion tank coolant came flooding out. Now I'm quite sure it wasn't overfilled previously, so why would it overspill? pressure in the system? Couldn't run it then check again as I had to leave before it would have cooled... Any ideas chaps? I have got a very slight and very occasional leak from the little hole on the front of the water pump which will be addressed when I get home.. this is apparently first sign of the water pump seal going, and the little hole is their specifically to allow water passing the seal to escape...

[Wicker Man]

The cap to the expansion tank is also a pressure relief valve. IIRC it opens at 14psi and vents excess air/steam/coolant. If the cap is serviceable the coolant system will find it's own level after a few warm up/cool down cycles.

For yours to overflow when the cap was removed with the engine cold is very odd. Maybe it wasn't completely cold or perhaps you have a poltaghost in your garage fettling your car?

[Chilliman]

Thanks Wicker Man, engine was cold, had been standing over-night.... bit of a mystery then

[bobfather]

It's likely that you've suffered low coolant level at some time recently. This will result in air being drawn into the coolant system via a very low header tank level. The air will then collect at a high point such as the swirl pot. If you have air in the system you are susceptible to localised boiling especially when that slug of air passes through the water pump and temporarily stalls coolant flow. That local boiling will force water into your header tank giving a false high level.

Check the level in your swirl pot, if it's low then that's your problem. Too little water, not too much

[Chilliman]

Thanks for the info Bobfather.... localised boiling doesn't sound good

[bobfather]

Chilliman said:

Thanks for the info Bobfather.... localised boiling doesn't sound good

Happened to me a few years ago, slow weep from the rad. If it's just a weep like mine was you can deal with it by maintaining the coolant level. The important thing is to ensure that the header tank never runs dry.

If your swirl pot is low then fill there, not at the header tank. Once full you can move the water a little by squeezing the coolant pipe at the top of the swirl pot, this should release more air to the swirl pot. Refit the swirl pot cap and leave the header tank cap off and run the engine until it gets warm keeping the header tank level above 50%. This will move any remaining air to the swirl pot. Let the engine cool, put the header tank cap back on and then recheck the swirl pot. Repeat if necessary.

Edited by bobfather on Thursday 2nd June 15:25

[Chilliman]

Thanks again bobfather, will be the first thing I do when I get home....