Cooling System Problem

[GreenV8S]

cbjroms said:

Surely a pressure cap will only allow air to vent if it is either opened or has an open bleed to the expansion tank?

The pressure cap is what separates the pressurised cooling system from the atmosphere. It is where gas has a chance to get out of the cooling system. If the system is sealed properly, it is the only place where gas can escape. Your cooling system should be designed so that any gas is carried to the pressure cap and accumulates there, so that when the system gets up to pressure what is expelled is gas rather than coolant. The usual way to achieve that is to have a settling tank where the coolant enters at high speed through a narrow pipe from a high pressure point near the top of the engine. The high speed ensures that any gas bubbles tend to be carried along by the flow. The settling tank has a large volume so that the coolant stays long enough for the gas to separate, and so it can contain the gas volume. The coolant leaves by a large diameter / low velocity outlet from the bottom which connects to a low pressure point at the bottom of the engine. The low velocity minimises the tendency to carry bubbles back into the engine.

[stevieturbo]

cbjroms said:

Really apprecaite this help - thank you everyone.

@stevieturbo - I hadnt realised that the air bleed needs to be always available (rather that just for filling). So I need a permanent and always open bleed from the highest point (ie thermostat hosusing) to the middle (ie above the water level but below the pressure cap) of the exampnsion tank. Thus, any air that finds its way into the thermostat housing will vent into the expansion tank and be replaced by the cooling system drawing water from the expansion tank?

@GreenV8s, the more I think about it the less certain I become about the geometry of the colling system. You say about getting the air to a presssure cap where it can vent out. Surely a pressure cap will only allow air to vent if it is either opened or has an open bleed to the expansion tank?

@tapkajohnD, the kit car is a Sammio (some photos here: http://www.madabout-kitcars.com/forum/showthread.p... I am not clear about the difference between a header tank and refill tank.Is it that my expansion tank does not have a feed from the top of the system and so it is only dealing with coolant exapnsion/contraction and not preventing airlocks?.

Yes, this is why I said to do it ages ago.

Part of the issue with people talking about tanks...is people call different tanks, different names, some of which may not be correct.

Your header tank is within the sealed system, it is under pressure during normal use. "bleed" to this header tank you have installed at a high level, and as already said, this will have a "fill" hose to return water into the bottom hose or similar.
In normal use, this cap should never vent or expel anything. Nor should the one on the radiator really.

But from this header tank, you could route a hose from the cap, to another open/atmos reservoir which is purely an overflow and with a suitable cap in use, any water expelled when hot, would get drawn back in as it cools.
But really....you don't need that. Just do it as I said ages ago, your header needs minimal water in it, just enough for you to see the system is full, and enough room for the water to go when it warms up without risk of any getting chucked out.

The cap on your radiator must seal, and only ever expel under excess pressure...it should never allow anything to be drawn back in as things cool.

[cbjroms]

Thanks again @stevieturbo,

Please be assured that I dont doubt anything that you have said. My questions are all about trying to make sure that I understand how the system should work.

The other thing that I am wondering is whether a stuck thermostat would cause the contents of the raidator to be pushed into the expansion bottle and out through its drain under pressure?

[tapkaJohnD]

This Sammio owner seems to have had the same problem:


Albeit the picture is difigured by a Photobucket logo, they have a header right up on the bulkhead.
See: http://www.madabout-kitcars.com/forum/showthread.p... about three quarters of the page down.

[cbjroms]

@tapkajohnD - thanks for that image. I have seen some other Sammio fixes but not that one which looks very neat. So the themostat housing is connected into the top of the pressurised reservoir (which makes it the highest point at which air will collect) and the radiator top connection goes into the bottom of the reservoir. Guess that this would be no better/worse than venting thermostat housing into the pressurised reservoir?

[GreenV8S]

Ideally you would only take a small part of the top hose flow, and feed that back to the pump inlet.

[stevieturbo]

tapkaJohnD said:

This Sammio owner seems to have had the same problem:


Albeit the picture is difigured by a Photobucket logo, they have a header right up on the bulkhead.
See: http://www.madabout-kitcars.com/forum/showthread.p... about three quarters of the page down.

In theory that should work....bit of a messy way to go about it though. And as long as the caps used are of the correct type.