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MG MGA - Which radiator cap

I live in a hot climate near Houston. My radiator cap needs to be replaced and I am curious as to which radiator cap I should use. A 4lb or 7lb ?
david kirkpatrick

7 psi when introduced was recommended as replacement / retrofit for earlier cars as well. Each 1-psi equates to 3-1/4 dF increase in boiling temperature. So 7-psi brings boiling temperature up to 335dF (beyond end of scale on the temperature gauge). With 50/50 mix of glycol and water for coolant, and 7-psi pressure cap, boiling point is more like 255dF (about 80 psi in the oil pressure scale of the safety gauge). Ergo, it makes no sense to use a pressure cap higher than 7-psi, unless you intend to install a temperature gauge with extended scale.
Barney Gaylord

Make sure you get the correct length. Many caps will fit in the radiator but don't seal because they are not long enough. If you use a short length cap, your heat temp will rise as it is not pressurized.
JEFF BECKER

Try the Stant R-6 from NAPA. Marvin,ct
Marvin Stuart

David,
Just remember, the 3 PSI increase puts more stress on your cooling system. That includes radiator, hoses and core (freeze) plugs. I went back to a 4 PSI cap after I blew out a core plug on a long uphill climb.
Make sure your system is in excellent condition if you go to 7.
Cheers,
GTF
G T Foster

I have had the same problems with my MGA's. I find that I need to have the radiators professionally cleaned (ie tank off and rodded out) every four or five years.
Barry Bahnisch

This thread was discussed between 24/02/2014 and 27/02/2014

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