Header tank cap issues

[Fox3]

I'm losing coolant from, what appears to be the header tank cap. I've changed the cap for a new one and it’s still the same.

What purpose does the tiny hole on the left hand side of the neck of the tank do? Mine spews out coolant when topped up to the correct level, but from what I can see this is sealed between the two O-rings on the cap.

I've been chasing my tail with the coolant system for some time now, the previous owner repaired a leak with a 'few' tins of rad-weld that I'm pretty sure has caused a number of the issues I've had.

Any help would be much appreciated, I'm going through about a litre of coolant a week at the minute!

[fandango151]

Silly question but when you say correct level where do you mean ?The level is actually a max marker in the bottom of the tank not the neck so looks pretty empty. If it is filled to the brim it will overspill and pop passed the cap.

Sorry if it sounds patronising but the header tanks are not intuitive on these.

[Fox3]

Thanks for the reply, I can see the max 'step' in the bottom and try to avoid overfilling it.

It seems to spew out until the heater goes cold, then requires about half a litre to get back up to the min level

[trikey]

Thanks for the reply, I can see the max 'step' in the bottom and try to avoid overfilling it.

It seems to spew out until the heater goes cold, then requires about half a litre to get back up to the min level


Try changing the tank next, I have heard of one or two being the culprit.

[T-Cut]

What purpose does the tiny hole on the left hand side of the neck of the tank do?

Read this: https://www.the75andztclub.co.uk/forum/showthread.php?p=2293452

I'm going through about a litre of coolant a week at the minute!Are you sure all that is being lost via the header tank cap? Diesels rarely get warm enough to have pressure cap ejection issues, but are prone to simple leaks. A common leak spot is the thermostat housing. Both the main housing o-ring/gasket and the coolant rail to housing o-ring are common failure points. Of course coolant might leak from any of the dozens of joints in the system. It may need careful examination to find them.

TC

[Fox3]

Thanks TC, very nice piece of work there!

I've fixed a leak near the FBH location and the top radiator elbow.

I cant see any evidence of coolant elsewhere, apart from the top of the expansion tank.

I did have an issue with it holding pressure for days, I've found another thread on here with similar symptoms to mine, it turned out to be a blocked oil cooler.