Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Engine running cool but losing coolant

On my Black Top Zetec, I had a leak around the seam of the plastic expansion tank.
Coolant was evaporating off and escaping through the seam.
Almost impossible to notice!
By replacing the tank, it was cured.
The tank on mine was a Ford part, with the part number only visible once the tank was inverted.
On initial enquiry, my local Morgan dealer, Rutters and MMC we’re out of stock.
The local Ford dealer obtained the part in 4 hours!

So is your plastic "expansion tank" a pressurised tank with a pressure cap or just an overflow tank where the pressure cap is actually at the radiator end.

My Silvertop is a pressurised expansion tank and I replaced the old black metal original with one of Simon's (Sifab) aluminium jobs when I replaced the radiator.

I wonder if the Black Top Zetec is plumbed the same as the Silver Top?

Bob
The expansion tank is pressurised on my Black Top.
Not sure about any plumbing differences.
Maybe worth having a chat with Sifab?

If it's pressurised, the plumbing will be very similar.
I was just a bit surprised that they had a plastic pressurised tank.
We live and learn.

Don't know if its related but I can tell you about drilling a small hole in the thermostat - perhaps.

Many moons ago I had a Cortina 1600. All was fine until I had a hose leak. Simple fix you may say. Well yes but after that the engine would warm up, get too hot and then boil - if it got past that it was OK. Thermostat (checked opening with thermometer) and fan all OK - it took me weeks to sort it even got new thermostat. Decided it was air in the system after even after bleeding and despite best efforts couldn't stop it overheating on the way up to temp.

Looking at the castings I decided that air trapped in the t/stat housing was the problem. Or, for some reason the thermostat sensor was too far from the block so wasn't being heated fast enough to stop over heat. Solution - drill a very small hole in the thermostat to allow air and a very small flow of water to bleed through - Problem Solved forever.

Funny but some months later see neighbour out under the bonnet of his Escort (same engine!) got the same problem - drilled a small hole and sorted...he thought I was a genius.

So small holes drilled in thermostat - probably the same reason...??

If I rev the engine, a large volume of coolant pumps into the plastic tank from the small bore hose upper left. Meanwhile the level in the tank drops as coolant is sucked out through the larger hose bottom right. This has been the same on 2005 - 2016 cars. So its definitely pressurised.

It may have been done for that reason but with the "modern" Zetec engine it's unnecessary because it's a double acting thermostat which already allows some water to bypass when cold and as the coolant heats up the thermostat gradually closes off the bypass as it starts to open up the main outlet to the radiator.

That way it can maintain a very precise temperature with no sudden cold shunts when the thermostat suddenly opens.

It also has a small ball check valve to allow air to bleed out to avoid air locks in the thermostat housing.

When I was struggling to understand why someone had drilled the thermostat, I bought an old housing and thermostat on Ebay to study it's operation and I was quite impressed how it works compared to the rather crude system on my old MK1 Escorts. (I've had company cars and motorbikes since then so I haven't tinkered much recently)

That's why I say on the Zetec, I really don't understand why they drilled the thermostat. Unless they had a problem somewhere else in the system and this was quick fix rather than really sorting the problem.

Hi all. Thanks for all the hints and tips.
To answer some questions there is no white smoke in the exhaust and not oiliness in the water that I can see
Plastic expansion tank under pressure as all have said.
I don’t know if the stat was checked and I need to find out as that’s really the next thing to get cleared off the list.
I’ll get the MOT out of the way this weekend first and then get it sorted out before the summer.