View Full Version : No pressure in expansion tank

05-22-05, 12:38 PM
I just had another engine put in my car and since I have not had any pressure build up in the coolent tank. I can drive for hours and take the cap right off with no pressure at all...Is this normal.

05-22-05, 08:44 PM
No, sounds like a leak. Do you have any problems? It may just be a bad cap.

05-22-05, 09:05 PM
Kinda sounds like a bad cap. If so and the cap is not sealing and holding pressure I would suspect you are overheating as the coolant will boil at 212 degress unpressurized.

05-22-05, 10:45 PM
Yea, I would say it is pretty unusual to have no pressure in the system. Replace the cap first. It sounds like it isn't sealing. YOu have to really press down on the cap and turn it past the locking tabs to seal it fully so make sure it is installed correctly. It will turn a certain amount with a normal turn but then you have to depress it firmly to move past the safety locks to allow it to be tightened to where it will seal. Maybe it is just loose.

If the cap doesn't do it then start looking for leaks in the system that would allow pressure to escape...

The system would boil at 212 F with no pressure only if it were filled with pure water. Pure water boils at 212 F but a 50/50 mixture of coolant/distilled water should be good for about 228 or so I think with no pressure. The coolant helps raise the boiling point considerably and so does the pressure in the system.

05-23-05, 01:38 PM
I do not have any other problems. The car wants to overheat but it is related to the fans which I will post a different thread. I am not loosing any coolent and I took off the hose off the bottom of the tank to make sure it is not clogged, it is not though.
I will replace the cap and go from there. Will post results.
Thank you.