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MG MGA - Radiator cap

I am thinking of fitting an overflow tank to my radiator. I have read the archives and it seems straight forward enough. I realise it doesn't do that much but will give me an idea of what the coolant level is, without me having to top up all the time, just for the radiator to dump it out again later.
The archives explain that I need to have a one way valve in the cap so that the coolant sucks back in when it cools, and says that most caps these days have the valve. But I called Moss and they had no idea what I was talking about! Obviously I need a long reach cap. Does anyone have the part number or know where I can get one please?
Thanks, Graham
Graham V

Graham - All automotive pressure caps for the radiator have the one way valves in them. As long as you get the long reach cap you will be ok for the coolant recovery system. Cheers - Dave
DW DuBois

MGAguru has this covered:

http://mgaguru.com/mgtech/cooling/cool_126.htm
Nick Kopernik

Thanks for the post. I did also call MGOC who said their one (GRC103) definitely didnt have a one-way valve. And I have tried checking some of the others on Barney's site, but without luck.
Graham V

Graham

You need to decide which type of system you want, pressurised or unpressurised. I have the pressurised version which uses an MGB expansion tank. Modern cars use this system.

With this set up a blanking cap goes on the radiator and the pressure cap on the expansion tank.

Steve
Steve Gyles

Hi Steve
Yes of course you are right. My terminology may have been incorrect but I was thinking of just having a very simple unpressurised system. From what the archives suggest, even though unpressurised, it should still suck back coolant from the overflow tank, provided the radiator cap has the one way valve in it.
Graham
Graham V

Steve,
when you say unpressurised, does that mean that the cooling system would be unpressurised?

If so then the coolant would boil at 212 degrees instead of approx 230 degrees.

So wouldnt pressurised be the best option?

Colyn
Colyn Firth

Colyn
Steve is referring to the overflow tank only. In his pressurised system, the entire system will be under pressure. In the unpressurised system, the radiator, is under pressure in the normal way, but the overflow tube leads into a bottle which catches overflowed coolant, rather than it going on the floor. But as I say above, even though its just a "catch it bottle", the radiator should still suck the coolant back, provided the over flow pipe from the rad neck is at the bottom of the overflow tank, so always under fluid level.
Graham V

I see what you mean Graham, thanks.
Colyn
Colyn Firth

Colyn

Sorry if I confused you. My system is one of the two types that can be incorporated. Both systems retain full pressure in the radiator. Mine extends that system pressure into the second tank by transferring the pressure cap to the expansion tank and fitting a blanking cap on the radiator. My expansion tank is from an MGB and is designed to hold system pressure. This is my layout: http://www.mgaroadster.co.uk/radiator_expansion_tank.htm

The other system which is what Graham is looking at allows any suitable (non pressurised) container to be used. This requires the pressure cap to be retained on the radiator.

Steve
Steve Gyles

Graham - See the article, Expansion Tanks, Coolant Recovery Systems, and How the Cooling System Works in the Other Tech Articles section of my Homepage at: http://homepages.donobi.net/sufuelpumps/
While I hate to disagree with the MGOC, but the original radiator cap does, in fact have a one way valve (or vacuum check valve) on it - see Figure 1 of the article above.

"My system is one of the two types that can be incorporated. Both systems retain full pressure in the radiator. Mine extends that system pressure into the second tank by transferring the pressure cap to the expansion tank and fitting a blanking cap on the radiator."
Steve - all you are doing above is to transfer the pressure tank from the one on top of the radiator to an external expansion tank. This is not a coolant recovery tank. See the article above. Cheers - Dave

DW DuBois

Good article David, well explained. May I add your link to my web page to direct readers to your article?

Steve
Steve Gyles

Dave
Thanks,an interesting and comprehensive article.
Both my radiator cap and my spare cap only have one rubber seal, the primary seal with no secondary seal. But reading your article I assume that doesnt necessarily mean they dont have the one way valve, as otherwise, the system would be under stress when it was cooling down? I cant see the valve but guess it is there?
Thanks, Graham
Graham V

This thread was discussed between 26/05/2016 and 28/05/2016

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