Thread: TD5 Losing coolant through expansion tank overflow.

Start with the simple cheap stuff.

Remove the cap and have a good look at its Orings they only
seal on the outer edges as you look at them horizontaly.

If they are not round in profile replace then or the cap complete
if you have not changed the cap in a few years.

The cap controls the pressure in the system it very important.
Not unusual to find more leaks after fitting a new cap as you
may have been running cooling system on a lower pressure the
new cap may increase pressure and show new leaks.

If it was mine I'd top up fit a new cap get it hot bleed off any air
from top hose as keep an eye on the level.

Fitting a catch can or bottle to the over flow pipe would be
a good idea if the head gasket is presureizing the system
more than the good new cap can deal with it will push coolant
into the over flow.

Cap needs to be tight to seal properly.

Daisy Driver,

A few questions first before I comment more fully.

Does the coolant leak only when the engine is hot but switched off?
Do the hoses feel hard and pressured?
Is the surface of the coolant in the expansion tank clean?

The symptom you describe may be an early indicator of head gasket failure but it may be something simple. The temp gauge will likely stay at normal even with a failed head gasket and only rise when coolant level falls.

Nick

Nick

I haven't checked for a leak with the engine off yet (bit cold and dark just now, will check in the morning when I get to work). The 'cap on, cap off' check was done with the engine running.

The hoses are 'squashable' and when you squeeze them the water level in the expansion tap goes up momentarily. There is no noise sloshing noise either so I am confident that there is no air in the pipes.

I had a good look at the water in the tank and it is clean, froth free and not smelly. There is no lunge under the oil cap or on the dip stick either.

I invested in a new, OEM expansion tank cap today and drove back from work with a plastic cup set up to catch any drips. When I got home the cup was still dry. I'm not counting my chickens and I would still appreciate your thoughts. Knowing my luck I might end up with a cup of drips in the morning...

David

Looking good David,

Sounds like it was a faulty cap only.

Another good test of the head gasket and cooling system is to drive it hard up a long hill when already at operating temp and then check under the bonnet, all should still be good if there is no problem.

Nick

"Does the coolant leak only when the engine is hot but switched off?"




What that indicate???? I have a Mercedes diesel that does that.


It lets all the coolant out via the cap after you shut it down.


Other than that you can let it idle for hours and doesn't use any coolant.

ntguy,

When you stop the engine cooling stops and the latent heat of the engine is no longer cooled by coolant flow and thus pressure builds particularly if there are gasses and diesel traces in the coolant from gasket and head problems which can be enough to push coolant out of the cap.

Nick

Agree with pippin! sounds like head gasket issues,will only get worse if not seen to.
Can you hear any gurgles from the heater matrix? this is another sign of gas buildup from a leaky gasket.

Trev.