Radiator Cap Issues

[tcrist]

Anyone have a radiator cap seal intermittently?

Griffin Radiator and inline tee for the radiator cap. 16 LB cap with anode.

I made a tester so I could test the cap and the tee at the same time. First time air just blew straight through with no restance at all. I changed caps to an 15-18 lb old leaver type and it did the same thing.

Changed to an old tee that I had and no air would blow through using either cap.

Changed back to the Griffin supplied tee and no air would blow through with either cap. Makes no sense to me.

My issue is losing coolant. The faster that I drive the more coolant I loose.

Then after checking everything and making sure that everything was tight I was adding coolant with the engine running (I put the cap on so as not to loose coolant until the thermostat opened). I was not even up to temps and coolant was pouring out the overflow. The cap was tight.

I also checked the thermostat again and it was working fine.

Any ideas?

[clasim]

Are you blowing air into the overflow connection ?

If you're using a cap w/ a dangle vent then your results could be normal, a cap w/a spring loaded vent will seal tight every time.

If coolant is blowing out the overflow before the engine warms up and you're using a cap w/a spring vent, you've blown a head gasket - that's the only way enough pressure could build inside the cooling system that quickly. If you're using a dangle vent cap, you could blow coolant if the vent is stuck open, replace it.

If you're loosing coolant you've got either an external or an internal leak, hopeing for the former.

[CHANMADD]

I did not see an overflow tank in your pics. Make sure that you have an overflow tank,(1965 era mustang tank works and looks good). The radiator cap should have the little valve that allows coolant to flow back to the block from the tank. Also 16 lbs is too much, change it for a 13 lb cap. The coolant will expand as it warms and if this overflow system is not in place you will have these problems.

[tcrist]

There is a custom overflow tank. See picture 1759 on the passenger side of the fan shroud.

The issue that I am possibly seeing is that either of the caps that I tried, holding pressure is inconsistant. One time you can just blow right past it with no restance and the next time it will take the 16LB of pressure before the cap lets the pressure past. This is using the Griffen supplied inline cap tee.

I am going to try it again tonght and see if I can see some sort of consistancy. Either with the Griffin supplied tee or the old tee that I had in the garage.

[Rick Parker]

Terry:
If you are using a recovery tank the cap on IT must be rated higher pressure than the one in the upper hose which you are using for the fill point. The fill point must be the highest point in the entire cooliong system too. The cap on the fill point must seal in 2 places. 1 at the bottom of the neck annd also at the very upper surface as well. You may have the wrong cap at the fill point OR you as mentioned may have a compromised head gasket. Pressurize the cooling system and see if it will hold pressure.

[danw]

For what it's worth...A radiator cap with what is essentially a bayonet-style closure can be applied in two orientations, 180 degrees apart. The first thing I would suggest is to try the cap on one way and then the other and see if the problem only shows up half the time. Good seal/bad seal may depend on your orientation. Kind of like good cop/bad cop (or maybe more like good girl/bad girl...)

[CHANMADD]

You cannot have two pressure caps. If your recovery tank has a pressure cap then it is not a recovery tank ,but an expansion tank. The tee piece in that case should have no spring cap and just seal the top and the expansion tank should then have another overflow/recovery tank attached after the pressure cap.this recovery tank should not be pressurized. The cap at the tee also then becomes the highest point and the point at which to fill.

[tcrist]

The tee piece is the only one with a pressure cap. The other one is an overflow/expansion tank. I tried all I could tonight to get the cap to leak and it would not. The tee piece is the highest point of fill.

[*13*]

You have a blown head gasket between the cylinder & the coolant passage. If you weld that cap on you'll blow a hose.