Hi All,
After a good drive today, I noticed that as the engine cooled, the top main radiator hose collapsed as flat as a pancake. When I opened up the overflow tank cap, it seemed to relieve some pressure and the hose returned to it normal round state.
What would cause this?
Thanks, Bob
Faulty cap on the overflow tank. It should always open to vent negative pressure.
Regards,
Ray L.
Ray. Help me understand what you are writing. The cap on the overflow tank is a pressure cap that retains pressure in the cooling system until that pressure reaches either 7 PSI for a non-AC car or 13PSI for an AC equipped car. At that point pressure is vented down the hose connected to the overflow tank neck.
The cap on the radiator, on the other hand, doesn’t respond to pressure. It simply seals the top of the radiator neck. There is no spring and seal assembly like on the overflow tank cap.
My first guess would be that Bob might have the wrong kind of cap on the radiator.
Actually, the cap on the radiator does not have any spring, it is a plain flat cap.
The overflow tank has a 7 pound cap with spring. I just removed it and looked more closely at it. I used some metal paste polish to clean it. There was paste residue around the center brass piece that I assume moves to relieve the pressure. I just cleaned this up and have reinstalled. I will try later if this worked. If not, I will need to buy a new one anyway, as this XKE has A/C. Looks like it should have a 13 pound cap.
Thanks! Bob
Two caps on an S2. The radiator cap seals the radiator neck, but is not a pressure cap. It leaves the tube to the header tank open at all times. The header tank should have a standard 13lb pressure cap (since you have a/c), which will have a spring loaded poppet in the center of the seal to allow air to return to the system. The symptom may indicate a bad pressure cap, restricted connecting hose between the radiator and header, or simply a weak upper hose.