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Zetec Expansion tank
Plunky - 23/10/16 at 03:19 PM

Afternoon,
I have been having some issues with the coolant expansion tank on my Zetec powered F27.
A little while ago the tank split, so I replaced it with a Renault Clio one, with the blue cap.
I am now getting a build up of pressure and the cap keeps letting go, getting the car and my legs a bit wet!
Has anyone else experienced this? I've looked and there seems to be a brown cap that is a slightly higher pressure, would this rectify the problem?
Thanks,
Liam

britishtrident - 24/10/16 at 06:50 AM

Assuming there is nothing wrong with the plumbing layout and the thermostat isn't stuck shut it sounds like a head gasket issue.
Over pressure was probably the cause of the original tank splitting.

The enginge plumbing should have a route for coolant to re-circulate from the engine side of the thermostat back to the water pump inlet. This called the by-pass circuit and is normally a constant hot flow through the heater on the donor. If you don't have this connected or are using a water rail this could be the problem.

Plunky - 24/10/16 at 07:45 AM

It's a brand new engine so I would hope it's not headgasket!
The split tank was on the old engine.
Does anyone have a diagram of what the plumbing layout should look like and I'll double check it is correct.

rm0rgan - 25/10/16 at 01:28 PM

quote:
Originally posted by Plunky
It's a brand new engine so I would hope it's not headgasket!
The split tank was on the old engine.
Does anyone have a diagram of what the plumbing layout should look like and I'll double check it is correct.





Try this...

Plunky - 26/10/16 at 05:43 PM

Just checked, and the plumbing layout is the same as the diagram.
The car itself doesn't overheat.
A new, higher pressure cap has arrived so I'll give this a try when I get the chance.

rm0rgan - 28/10/16 at 10:27 AM

quote:
Originally posted by Plunky
Just checked, and the plumbing layout is the same as the diagram.
The car itself doesn't overheat.
A new, higher pressure cap has arrived so I'll give this a try when I get the chance.


I find that my expansion tank settles just below the minimum level mark in the expansion tank on my zetec MK when cold - if I top it up, it evacuates it out of the cap too - maybe you've overfilled it and it was just venting the excess to settle at the right level/pressures as I think zetec expansion tanks are quite a bit bigger than Clio ones from pictures I have seen. They hold around 5ltrs of water/antifreeze mix in a Mondeo whereas we probably hold a couple of litres less at a guess given lack of piping, heater matrix etc...