Water circulation.

[kentishvanman]

Just been discussing a water problem that a fellow T3 owner has.
Water system topped up as should be. Coolant expands into expansion tank but will not return.
A new 'dalek' cap, from Brickwerks, has been fitted but not solved the problem. He and his garage cannot solve the problem. Hose from one tank to the other is fine.
Any suggestions.

[AngeloEvs]

It must be sucking air in somewhere but that is not a fat lot of help I know. Small crack, porous hose, poor connection, bleed valve if later thermostat type, garage has probably checked all those. I suppose they could pressure test the system.

[RogerT]

So if coolant is not returning through the dalek cap, that suggests either there is a part of the system collapsing under the negative pressure, rather than maintaining its shape and drawing coolant through the cap; or, the negative pressure is drawing air into the system through a small leak rather than drawing through the cap. In the second case you would expect to see air in the tank, or at the bleed points - I guess maybe not visible when the engine isn't running, but maybe just after starting when the coolant is still cold but has pushed the air round the system so it reaches the high points.

So 1, a weak hose; 2, a leak which doesn't leak under pressure - is that even possible?

E D I T Angelo types quicker than me, and more succinctly...

[Ian Hulley]

What engine and year please ? Auto or Manuel ?

The only time I've ever had similar symptoms was in the days pre-Brickwerks with a succession of faulty GSF Dalek caps. Blow through the Dalek cap spout ... Does it 'toot' ? If not it's knackered, if it does then move on to look for other causes.

Is the top-up tank on 'Max' when cold and higher when hot ? Is there any oily deposits inside the Dalek cap or header tank ? All hoses and pipes hot when engine up to temp ? Heater working ok ? Open the bleed valve on the top of the t/stat housing (late system 1.9/2.1 petrol) any bubbles in the bleed ring back to the header tank ? Check for coolant crystals on the reverse of the t/stat housing (they often crack and drip but evaporate on the hot exhaust directly below) check for drips below the water pump gland.

Ian

[Mocki]

i would make sure all levels are where they should be, drive it untill up to working temp, then park it up over a dry clean floor ( card board or plastic sheet) and let it cool
whilst letting it cool do not open the darlek cap, keep the pressure in the system, and take a look and (More importantly) listen for any air movement or coolant leakage.
does it hold pressure untill its properly cool?
if you can find nothing,but it did loose pressure , turn the heater off ( assuming the heat valve is working and the heater does turn off) and again get it up to temp ( after making sure the coolant levels are as they should be ) and repeat the process .
it is not unkown for the heater matrix to leak slightly and suck air in
same with rad, almost impossible to see when hot as the coolant it looses is so little and it evaporates on the rad

[bigherb]

So 1, a weak hose; 2, a leak which doesn't leak under pressure - is that even possible?

Definitely. Expansion of joints can seal up. The most common is the joint between the radiator core and the headers