Coolant leak. 1985 1.6Turbo diesel

[kaptan]

My 1985 1.6 Turbo diesel has a persistent coolant leak which I cannot find. Every trip I lose about a 1cl per mile, so the morning after a 50 mile trip it takes about 3/4 of a wine bottle to bring it back up to the mark.
I have been unable to find where it is leaking. It does not overheat, the temperature guage needle stays in the middle. All appears dry underneath.
There are no traces of water in the engine oil.
No signs of leakage from the water pump.
Radiator and Heater matrix have both been replaced and all hoses inspected.
The pressure release cap opens and closes at the correct pressure
When system is pressure tested to one atmosphere it loses its pressure very, very, slowly.
A tear drop once every 5 minutes comes from the electric fan temperature switch seal in the bottom of the radiator.
This can only be seen when system is pressurised, no signs of it when engine running at normal temperature.
The filler cap in the expansion tank is a plain screw on plastic cap marked water.
Is this correct or should it have one with a breather?
When the coolant warms up and expands the level in the expansion tank rises but if there is no breather won't the pressure increase until it opens the pressure release cap?
Any suggestions please.
Thanks Chris.

[clift_d]

The expansion tank is the one behind the number plate flap and that has a plain cap. The header (main coolant) tank in the engine bay should have a 'dalek' cap with an expansion hose to the expansion tank. As the coolant heats up and expands it should displace into the expansion tank through the dalek cap. When the engine cools it should get sucked back into the main tank by the same route. The main tank should always be full to the brim and the expansion tank should be maintained between the Min and Max lines. There should be enough air in the expansion tank to allow the necessary fluid expansion from the main tank.

If all that's working then you'll need to start looking for drips. Put some blue paper around joints and connectors. Check hoses for splits and perishing. Run the engine a bit and see where you get fluid. That tear drop you're seeing shouldn't be there so maybe there's a gasket that can be replaced. You'll just need to track it down if it's nothing obvious.

[lloydy]

the expansion tank behind the flap is vented, not the cap. there is a raised spigot right at the top that has 3 holes in it. 3/4 a bottle of wine in 50 miles is quite a lot, you would like to think you would see that. Do you get a lot of white smoke when you 1st start the engine?

[simoncummins]

I had this problem turned out to be a warped thermostat housing. Leave it over night then with a torch look down the back of the water pump (the other end to the pulley) There is a little ridge in the crankcase casting this may have some water in it if so its coming from plastic thermo cover. You dont see it under the engine cause it evaporates when the engine is hot. Took me weeks to find this and £3 to fix it hope this helps. Simon C.

[Oldiebut goodie]

^^^^ WHS When I removed mine it had warped so that it was oval and would not reseal and continued to drip! Replacement only solution but are cheap enough.
Another suspect is the heater valve under gearstick area - usually you can smell that one though as you get a warm antifreeze smell waft up through the gearstick gaiter. Winter usually as it isn't hot in the summer normally.

[kaptan]

Thanks for your replies I'll follow them up and let you know the outcome.

[kaptan]

I've just been told, following a test. That if you run the engine until it is warm, then remove the dalek cap and take the engine up to 3000 rpm and it blows out a lot of water it indicates a leak in the head gasket.
Is this true?
If a leaking head gasket pressurises the cooling system surely the water has to go somewhere?
No sign of water escaping.
If there is a leaking head gasket won't it let water into the engine when it cools down?
No sign of water in oil.

£650 to plane head and fit new gasket, but no guarantee that this will solve the water loss problem.
Your thoughts and advice please.
Chris.

[Oldiebut goodie]

You shouldn't skim/plane diesel heads says Mr. VW.

[windy]

Put ultraviolet dye in the water, then go looking with an ultraviolet lamp in the dark....