Leaking a little coolant when radiator cap is tight

[Russkcpa]

My 1973 Tii will leak a small amount of coolant (most likely from the overflow tube) if my cap is tight. If LOOSE I do not have any leaks. Any suggestions?

Russ

[Chris_B]

The cap may be weak.

[Biscuit3]

There are two radiator caps available on the market. One for a radiator with no overflow, and one for a radiator with an overflow. It should specify on the packaging of a new cap as to which it is.

Either you have the one for non-overflow, or too much pressure is building up within the radiator and it has no other way to get out besides leaking down the sides, hense when looser, everything is ok. This can also cause problems with too much pressure as sooner or later, one of your hoses is going to burst as well.

[c.d.iesel]

overfilled when cold?

using correct BMW cap?

uneven sealing surface inside the

radiator filling neck so the cap seal

don't seal good?

[Guest Anonymous]

When the cap is loose the radiator pressure doesnt build so no coolant will be forced out, my suggestion would be to pickup a radiator pressure tester and put about 15 lbs. of pressure on the system and you will be able to find your leak..

Marty

Chesapeake va.

[BillyRay]

(most likely from the overflow tube)

First off, figure out exactly where it is leaking from. There are many places that are possiblilities. I just went through the same thing, pressurized the system and found the "weep hole" at the bottom of the water pump was the culprit.

Best Regards, "Z"

[ingraham]

After filling the radiator, it will blow off excess coolant for a couple of hot/cold cycles, and then the cold level will be about 3/4 inch below the neck. Did you recently top it off?

Radiator caps are consumables, and they're cheap. Try a new BMW cap.

[SteveJ]

If you want to spend $50 or $70 or so on a really usefull tool, get a Stant cooling system pressure tester. A model 270 as I recall. I got mine used off of Ebay.

You can pressure test the whole system which makes it easy to look for leaks from loose hose clamps. You can also test the blow off pressure for the cap. Is it good or is it bad? 10 seconds with the tester and you'll know. You can also use the tester to see if there are combustion leaks into the cooling system by monitoring the pressure as the motor runs.

Oh yes, carry a spare cap. They are inexpensive and tend to fail regularly.