Radiator and header tank cap confusion

[PainswickEType]

On my S2 4.2, I seem to be losing coolant from the header tank overflow. Usually just a dribble, yesterday about a cup full. Fairly certain the head gasket is fine, looked for the usual symptoms and can't see any problem. Engine runs at the right temp and normal levels of coolant. Seems to be worse since I turned the heating to cold.

I thought that the first thing I would do, is to change the radiator and header tank caps. It has a 13lb cap on the header tank and what looks like just a plain cap on the rad with no pressure relief valve. I have studied the Barratt catalogue and from what I can see, the rad should have a 13lb cap and the header tank a 7lb cap. It looks like something isn't right here??

Can anyone tell me what should be fitted please?

[tinworm]

You may not have left enough expansion room - fill with coolant so you can just touch the top of the level with your index finger through the filler.

Barrie

[mgcjag]

Neil...7lb on the expansion tank and a plain cap on the rad....Steve https://www.sngbarratt.com/English/#/uk ... mbly/21850

[Gfhug]

Neil, my understanding is that the S2 radiator has a plain cap and the expansion tank 7lb. As Barrie says, fill the expansion tank to about half level. You will find it’ll find its own level after a few runs. Yes, you will get it dribbling out from the expansion tank until the level is self-determined correct then it should stay steady. There are several comments on here if you search for “burp” to explain the system.
Thank you Steve for posting the correct info as I was typing.

Geoff

[PainswickEType]

Thanks very much Geoff Steve and Barrie. I will source a 7lb cap and re-try with the levels.

Neil

[malcolm]

May be obvious, but don't top up coolant in the expansion tank, just top up the rad. The expansion tank will find it's own level then.

[mgcjag]

Hi Malcom.....as per the service manual...fill the radiator...then fill expansion tank to its half way mark....Steve

[malcolm]

Aah, ok Steve. Maybe the "halfway" is the tricky bit. I used to do that, but always then had coolant out after a run. Just topping up the rad, my expansion tank is a bit below half (or so it looks) but I never get spillage and expansion tank never goes down.