Why won't coolant water interact with the expansion tank?

[Blue Babe]

My expansion tank level hasn't altered for a few months, but the level in the header tank keeps going down. Its a DF engine with a metal rad style cap on the header tank.

The cap was bought new about 18 months ago and appears to be in 'as new' condition. I have removed the connecting pipe and can blow through it OK, blowing bubbles into the expasion tank. I cannot see any signs of a leak from anywhere. If I take the cap off before the water is stone cold, the water level is to the brim but when it's cold it drops.

I've tried leaving it at the lower level to see if it was expelling an excess under pressure but it continues to drop with each trip. It does not expell into the expansion tank under pressure and doesn't draw up to replace as it cools. I suspected a minor leak may be stopping the system from pressurising, but a dose of Kseal hasn't changed anything.

Any advice would be appreciated please.

[Steve T]

Have a look at the links below, these are the tried and tested ways of getting the water system working as it should. If this does not work and you are loosing water then there is a another problem. Print them off, read a couple of times, digest, it will all make sense, also useful to keep in the van for use when needed.

https://club8090.co.uk/wiki/Co ... ing_system" onclick="window.open(this.href);return false;


http://www.brick-yard.co.uk/forum/bleed ... 29710.html" onclick="window.open(this.href);return false;