Testing Radiator Caps

[Joe/Ct]

How can one test an un-numbered radiator cap to see if it is working properly and to verify it's pressure rating?

 

[oldskool]

stant made a tester for pressure caps it had a hand pump and gauge not sure if they still make them

 

[G.M.]

stant made a tester for pressure caps it had a hand pump and gauge not sure if they still make them

They still make them, some mechanics have them or any radiator shop would have one. It's not only the pressure but a WORKING pressure cap has to seat and seal down on the washer like seat down at the bottom of the filler neck. Surprisingly most caps on old Fords don't seat at the bottom so you only have a plan cap. You can feel the spring action on the bottom seat before pushing the cap down to engage the locking prongs. If it don't reach the bottom seat a 1/8" thick rubber washer down on the bottom seat solves the problem. G.M.

 

[Joe/Ct]

They still make them, some mechanics have them or any radiator shop would have one. It's not only the pressure but a WORKING pressure cap has to seat and seal down on the washer like seat down at the bottom of the filler neck. Surprisingly most caps on old Fords don't seat at the bottom so you only have a plan cap. You can feel the spring action on the bottom seat before pushing the cap down to engage the locking prongs. If it don't reach the bottom seat a 1/8" thick rubber washer down on the bottom seat solves the problem. G.M.

I checked and my cap was apparently not seating properly in the filler neck....there was no spring to the cap when inserting and measured the same 3/4" for both the neck and the cap. As recommended, put a 1/8" thick rubber washer in the seat and ran to a show tonight. All seemed to be ok on the drive over (approx. 3miles), but when I got there, I was dumping coolant on to the deck (for you non-swabbies, that's the ground/road). Opened the hood and there were several pin-hole leaks squirting out. Might the cap be too high a pressure?

PS: Does anyone know of a good radiator guy in or near southeast Connecticut?

 

[ford3]

you didn't say what yr car, pin holes where? cap or radiator,? most older cars uses a#4 cap, hard to find, so #7 caps are used, and as, and as GM said, take the cap to a radiator shop and have them check it for pressure and leaking

 

[Joe/Ct]

you didn't say what yr car, pin holes where? cap or radiator,? most older cars uses a#4 cap, hard to find, so #7 caps are used, and as, and as GM said, take the cap to a radiator shop and have them check it for pressure and leaking

Sorry....this was for the '39 coupe in the pic. The cap I am using, from the info on the box, is part no. 75-8100-B, ID'ed for a 1937-48 vehicle, and is 4# pressure.