Aftermarket Overflow Tank For Radiator - How Much Coolant?

[some_cs_student]

Hey,

I've got an aftermarket radiator, with an aftermarket tank sitting above it that seems to be connected to it, both the small aftermarket overflow tank (Apexi) and the radiator tank have filler caps so its not really required its just there for some reason.

I've also got the stock plastic overflow tank on the side which is where coolant goes if it gets boiled out.

Anyway, with the top overflow tank, how *full* should it be of coolant? Normally I only put a little coolant in there but just wondering if that's the right thing to do....

The top overflow tank is connected to the radiator so the only place it can go to is the radiator....(unless the cap comes off).

Regards,

Gareth

[some_cs_student]

Is there a simple answer? I'm sure someone knows the answer...

[Craved]

got a pic?

if it has a radiator cap on it then it should have a line from just under the cap like a radiator that goes to the over flow.

[some_cs_student]

Image attached, I'm referring to the circled item, it's connected to the radiator, from the radiator, it can overflow to the standard overflow tank (drivers side plastic overflow tank), unfortunately I've seen that happen once

[Godzilla32]

Ok the stainless tank you have circled is called a radiator header tank. It must be mounted higher than any other part of the cooling system. As its job is to remove air from the coolant. It should be about half filled so there is room for expansion and contraction. The other standard plastic bottle is just an overflow bottle which will come into play during times like when you switch the engine off and there is no longer coolant circulating. Heat soak from the engine builds excess pressure in the cooling system which over comes the spring loaded radiator cap and over flows to the bottle. The reverse happens once the system cools and the coolant contracts, it creates a vacuum in the system and draws on the coolant in the overflow botttle. You dont really need both of these over flow bottles/header tanks. As the header tank does 2 jobs, removes air and keeps a consistent supply of coolant available.

Hope this helps,

Deren

[Craved]

Ok the stainless tank you have circled is called a radiator header tank. It must be mounted higher than any other part of the cooling system. As its job is to remove air from the coolant. It should be about half filled so there is room for expansion and contraction. The other standard plastic bottle is just an overflow bottle which will come into play during times like when you switch the engine off and there is no longer coolant circulating. Heat soak from the engine builds excess pressure in the cooling system which over comes the spring loaded radiator cap and over flows to the bottle. The reverse happens once the system cools and the coolant contracts, it creates a vacuum in the system and draws on the coolant in the overflow botttle. You dont really need both of these over flow bottles/header tanks. As the header tank does 2 jobs, removes air and keeps a consistent supply of coolant available.

Hope this helps,

Deren

+1

nice description

[some_cs_student]

Ok the stainless tank you have circled is called a radiator header tank.

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Deren

Thanks Deren, it all makes sense now, and an excellent explanation there

I have seen the overflow in use when the coolant boiled and went out of the overflow tank, I think I've got that under control now

I'll make sure to fill the radiator header tank about half-way, right now its using about 1/6 of its full capacity.