Leaking rad cap?

[dazandcaz]

I have been doing a load of maintenance work which includes replacing the thermostat, rad cap and usual flush/re-fill of coolant system.
When the re-fill of coolant was almost complete, i fitted the rad cap and removed one of the hoses from the heater control valve (on the bulkhead)to finish topping up through this hose to eradicate most of the air. While doing this i noticed that the resevoir was filling via the "vent" pipe below the rad cap.
Is this normal?
I thought that the rad cap sealed the system up untill a certain pressure and also allowed return flow under vaccum.
I tried it with the old cap and still the same.
Am i being thick? or is there something wrong?

dazza

[TonyN]

.
Am i being thick? or is there something wrong?

dazza

Nope, yup.

[dazandcaz]

Inside the neck where the cap sits is nice and clean with a smooth seat. The rad cap in question is an rtrax pattern one, would a genuine toyota one cure the problem?

[TonyN]

It depends, I've not had any trouble with them, measure the depth of the seat from the lip, and the width of the hole and compare it with the cap to see if it fits snuggly.

[dazandcaz]

Thanks, will do in the morning.

dazza

[dazandcaz]

Thanks for the suggestion about measuring the cap. I checked both caps i have (new and old) and measured the depth of the seat on the thermostat housing. All were the same but this meant there was no pressure on the sealing ring. After further investigation it looks as though the metal has worn away a little where the tabs hold the cap down so the fit wasn't as tight as it should be. A little pummeling of the tabs on the rad cap in the vice and it now sits nice and snug with no leaks.

One more problem solved, a thousand more to go!