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How to tell if Radiator Cap is bad...

3156 Views 5 Replies 5 Participants Last post by  66conv6
I've noticed over the last few weeks, the engine has been running a little warmer than usual, and I realize it's summer and it should, but after going across town (about 20 minutes of driving), and after killing the engine it starts to spew out the overflow hose, not fast like it's overheating, but enough to raise my concerns. Tonight after I had got back, I heard the pressure leaking from around the cap, with a little bit of moisture at the base of the radiator neck, so it would appear this cap is history, correct?

So my questions;

What should the correct pressure cap be for a 67 289 4v? (The one on there now is a 16lb. cap on a 3 core radiator). I was thinking 13lbs. was correct, but not certain now?

And has anyone purchased an Autolite Cap from Scott Drakes or another Mustang parts supplier, and are they worth the $25.00 asking price? I know I can get cheaper aftermarket stuff, but since that is one of the first things you see when you open the hood, I don't mind paying a little extra for the correct style as long as it will last for a little bit.

And last question, the correct finish on the Autolite caps should be Zinc Plated?
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My 66 says a 14lb cap but I can't find them so I use 13. $25 will by a number of Pep Boys caps. I don't think theres enough of a verifiable difference in quality to justify such a price unless its for concourse. I change my cap every couple years since its not worth the price to buy a tester to check it.
I have a 13 lbs cap on my 67. You might be able to get your checked at an auto parts store. If not Autozone loans tools for free. They may have the pressure tester for your cap.
The pressure relief you hear does does not necessarilly mean the cap is bad although it could be releasing at too low a pressure. The only way to know, unless you have a cap tester, is to replace. Why not convert to a coolant recovery type system. Does away with the tell tale dribble out the vent tube and more importantly allows the radiator to stay packed with coolant all the way to the top, hot or cold.
Got a picture or example? I'm looking for a plastic reservoir that will mount well (where the window washer baggie normally goes). I'm looking for one that is about the right size and shape that it looks good in the compartment. The best one I've seen so far is the one in my wife's 2002 Explorer... Still looking tho...
Got my recovery system at Pep Boys. Less than $10.
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