Radiator cap test

[duvel]

Time to tell the whole story; After a ride of a half hour leaks coolant out of the overflow tube.The temperature looks not to high ,seen on the indicator inside. If i press on of the coolant tube's, the air escaped on the overflow tube.Do that mean that i have a bad cap?

[gr_diver]

I've had radiator caps that their rubber gaskets were deformed from prolonged usage, and did not seal well, giving occasionally overflow...
If with the engine hot, you press the radiator hoses and see air/fluid escaping from the overflow tube, something is wrong. Probably the cap is worn, or the lip on the radiator's filler hole is dirty and does not allow the cap to seal well. In any occasion, I would clean the filler, and replace the cap, it is cheap insurance...

[Lindsay]

Stant 13 lb. radiator cap sells for approx. $10 U.S. dollars (or less). I would try another radiator cap and check results.

[duvel]

Problem solved ! It was the cap. There are 3 sealings in a cap ;
One on top closed everything
the second inside ; opens by a certain pressure and relief the pressure to the overflow

The third : opens when the system cool down and pulls the system in a vacuum.
The last one was bad in my case.
And if i press a tube with a cold engine,there is no air escaping at the overflow anymore .
Thanks all