[CrockPot]

What is the correct pressure rating for the radiator cap? I heard a tech manager say 8; the last one I bought was spec'ed at 11 psi; and when I look them up today, only 16 psi are recommended. Mine will push coolant to the overflow when hot, but it doesn't suck it back to the engine when cold. I opened it this morning when cold and there's still pressure on it, even though the radiator is low.

 

[ron1004]

Not sucking the fluid back into the radiator from the reservoir has nothing to do with the pressure rating of the cap.

There is a small non-return/check/vacuum relief valve in the cap that allows fluid to be drawn back into the radiator.

There's three seals that you need to check, one that seals the pressure in the system, one that seals the top of the radiator cap from atmosphere, and one that seals the check valve.

For it to draw fluid back in, the system must be 100% purged of all air - did you fully bleed the system?

Radiator Cap Function and Operation

What does a radiator cap do? The radiator cap maintains a constant cooling system pressure while allowing coolant to flow back and forth to the overflow or resevoir tank. As coolant heats it contracts. The cap acts as a two way valve the allows coolant to flow to and from the overflow.

www.freeasestudyguides.com

 

[CrockPot]

Not sucking the fluid back into the radiator from the reservoir has nothing to do with the pressure rating of the cap.

There is a small non-return/check valve in the cap that allows fluid to be drawn back into the radiator.

There's three seals that you need to check, one that seals the pressure in the system, one that seals the top of the radiator cap from atmosphere, and one that seals the check valve.

For it to draw fluid back in, the system must be 100% purged of all air - did you fully bleed the system?

Once the pressure was relieved, I replaced the cap and blew into the overflow tube. Air did go back in it. However, that does not explain how air is getting into the coolant system. It isn't consistent. I suspect a head or gasket leak that only occurs at high rpm. No sign of coolant in the oil, but there's a film of oil in the radiator.

 

[ron1004]

If all the seals on the radiator cap are good and the system fully bled, then the other likely source of air/gas is from a head gasket or a water pump mechanical seal.

You can take it to a shop that can measure combustion gas in the cooling system, pressure test the cooling system, and do a compression and leak down test.

 

[Gerard 2]

Is the cap the correct type for recovery systems? I reckon that pressure was negative pressure (vacuum) if it's not drawing fluid back to the radiator tank.