Radiator cap

[aboyandhisdog]

Quick question:  I flushed my cooling system today, and noticed that I have never had the issue of opening the cap when the engine is hot, meaning...there is no pressure built up.  I find that with everything hot, I can just unscrew my cap with no problem.  So, the question...is my radiator cap bad?  It is a 4# cap as suggested in the manual.  Is this the best pressure cap to replace mine with or is there a better pressure cap to get do you think?
Thanks!

[F Bill]

If you can find someone who can pressure test your entire cooling system  and cap that would be best.. You may have a loose hose or connection somewhere that is not holding pressure.  THey have a little hand pump and gage setup that attaches in place of the cap , using the right adaptor, that applies 4-10 lbs or so, then you look for pressure dropping and obvious leaks.

The cap is tested the same way.  It might take some searching to find someone with the correct adapter to pressure check it, depending on which radiator and cap your jeep has.

Or, just buy the new cap and see if it cures it.

[Carls_jeep]

Knowing how old the radiators are on our Jeeps and I couldn't find a 4 lb cap easy I got a 7  lb cap and a 160 deg thermostat. I decided to not seal the cap all the way, just to the point it is locked on but not sealed. Water boils at 212 deg and after I found my temp seldom gets to 190 deg and mostly at 160-170 I did not see a need to stress the radiator by building pressure in the system.

The only reason for the pressure cap is to raise the boiling temp of the water and since these engines don't operate that high like modern engines I saw no reason to stress the radiator.

[aboyandhisdog]

Good to know.  I always wondered the purpose of building pressure in the system.  Increased boiling point, makes sense.  Think I'll just try to find a new cap as I'm sure the system is very tight.  If the new cap doesn't build pressure, then I'll take it a step further.  Thanks a lot!

[aboyandhisdog]

Determined that the cap is just fine.  What I discovered is that last summer when I painted the radiator, I sprayed some paint on the inside of the neck where the rubber gasket of the cap rests.  Worked fine for some months, but as it heated and cooled, the paint must have formed an uneven mating surface on the neck of the radiator which didn't form a good seal with the cap rubber.  Cleaned it up and we're as good as new.  Thanks for your help.