I just shut my truck off and got out to check all the fluids before I went in and I squeezed the upper rad hose and it didn't seem to have much of any pressure..so I took the cap off and nothing..no pressure at all taking the cap off right after shut down..and I had been driving more than long enough for it to be heated up fully. No antifreeze on top of the radiator or anything that suggests a leak..not sure what it could be.

 

Is it cold out? Maybe it is just not getting hot enough. Is it over heating? Try starting it with the cap off, after it warms up and the thermostat opens, you should see some movement of the coolant...Mark

 

If it ain't broke, don't fix it.

If the engine temp is below 212° when you shut down, it only takes a short time for the pressure to go to 0. After that it pulls fluid in out of the overflow tank with a slight vacuum.

If the radiator is full to the cap, and the overflow jug is what you'd expect (pretty low in cold weather), then everything is working as planned.

Pressure in the system is only needed for coolant temps above 212°.

 

No its not overheating, and its not really cold today. I'll get a thermometer tomorrow and check the coolant temp after I drive it for a while. Thanks.

 

Pressure test the cap and radiator both should hold pressure, older truck most likely a 12 psi cap. If cap will not hold pressure then replace it.