Filler Tank Question

[Chunksta]

Guys,
I've fitted a new water pump, all watertight.

I've now bled the whole system, again, and again on ramps. Great help on wiki! Thank you.

Question though, is the filler bottle supposed to release coolant if overpressurising?

Mine has released coolant from the top of it, where there are two vents on a spout.

Is that normal, or do I have an issue?

[AdrianC]

The tank inside the catflap? It's not pressurised.

[California Dreamin]

Guys,
I've fitted a new water pump, all watertight.

I've now bled the whole system, again, and again on ramps. Great help on wiki! Thank you.

Question though, is the filler bottle supposed to release coolant if overpressurising?

Mine has released coolant from the top of it, where there are two vents on a spout.

Is that normal, or do I have an issue?

Two tanks:

Main pressurized tank in the engine bay and fitted with a pressure cap that on later versions (the majority of buses) looks like the head of a darlek (DR Who)
Second 'top up tank' (the one you can see behind the number plate)

From your description I think you are talking about the main tank..if so then YES, it is designed with two valves. The first valve that opens when the pressure reaches around 1 bar (this is due to the coolant expanding as it heats up), the excess coolant then flows into to top-up tank....so yes, it regulates coolant pressure to ensure it doesn't get too high.
Then.....once the engine is turned off and the engine cools, the coolant contracts, creating negative pressure in the system which opens the second valve in the pressure cap which then effectively sucks 'back' the coolant from the top-up tank that was previously deposited there.

Martin

[Chunksta]

Thanks Martin,

So what might cause so much pressure that all the coolant will bust out the filler tank to push the water over the filler tank threshold please?

[ghost123uk]

So what might cause so much pressure that all the coolant will bust out the filler tank to push the water over the filler tank threshold please?

"all the coolant will bust out the filler tank to push the water over the filler tank" is a bit confusing.

Is the main tank, the one on the left, staying completely full to the brim all the time?

The "filler" tank, normally referred to as the "top up tank", should be around half full. It gets fuller when the engine is hot, and less full when the engine is cold, but it should not overflow (unless you have over filled it).

If you have it correctly filled when cold (there are "min" and "max" marks on it), but it overflows when the engine is hot, this can indicate a head gasket problem. Any decent garage can do a "sniff test" with their exhaust gas analyser to test for that. It's a 5 minute job to test.

[California Dreamin]

Thanks Martin,

So what might cause so much pressure that all the coolant will bust out the filler tank to push the water over the filler tank threshold please?

Well it could just be a faulty 'DARLEK CAP' but if you could just answer a couple of questions:

Is the coolant pushed into the 'Top-Up' tank straight away or does this only happen after a run when the hoses are pressurized (feel hard)?
Is the pressure fully releasing (do the hose pipes go soft) after you see the coolant flowing to the 'Top-Up' tank?

The point is...this process should only happen 'AFTER' the system is pressurized and then 'ONLY' to release a bit of coolant at a time (so the hoses at this point should remain hard showing that they are still under pressure).
I would be tempted to buy another pressure cap before moving on to more sinister conclusions (head/barrel seals)... make sure its a good quality replacement as there are some very poor copies out there (Stick to Brickwerks to ensure quality).

Martin

[Chunksta]

Thanks Martin,

I bought a new Dalek today. The pressure takes some time to build up.

From cold, the filler tank behind the flap was filled between the two marks.

The engine gets hot, and as the thermostat opens, so the level rises in the filler tank behind the flap.

The radiator fan kicks in before the bus gets too hot, all working there. But if you leave the bus to run on, the the pressure rises further and pushes the water level up in the filler tank behind the flap, to a point where the water flows out of the two little spouts at the top of the bottle.

Will try the dalek tomorrow and let you guys know.