Coolant Pressure

[Ncostello]

I recently installed a new radiator, hoses, Cummins thermostat etc etc. I filled up the system and have ran it several times up to temp. Everything seems fine. Except even after sitting for a few days... . the upper hose is still "solid" and I can't pinch it together when cold. And my overflow bottle level never moves.



I chose a 13psi Stant cap. I decided to try a 7psi cap and see what happened. When I remove the cap cold... I got a purge of coolant as if under a little pressure.



Is it possible I filled it completely full with no air whatsoever? I did this while it was warming up the first time... then I put the new cap on.



Kinda makes me think head gasket failure is causing pressure in the system. But I have no other indications of such a failure. Can pressure get in the system and yet no coolant backflowing into a cylinder?



This is a stock truck and shouldn't have a gasket failure. Boost has always been stock level.



Besides this issue, what cap should I be running? 7 or 13? Factory was 15 and was still on the truck when I did this work. I know the higher pressure gives a higher boil point... but I'm at elevation 520 and probably will never see anything too much different with this truck.

 

[JLEONARD]

You need to make sure the hose from under the rad cap is clear into the overflow bottle. Sometime sediment collects and blocks the hole into the bottle and will exhibit a similar scenario. Remove and blow thru.

Not sure what cap is proper... put the old one back and see what happens?

 

[Ncostello]

I replaced that hose. And the overflow bottle was removed and cleaned inside and out. It was pretty clean anyhow. So that can't be it.



15psi was the OEM cap pressure. Seems like an industry standard.



I've just never had an upper hose do this after its cooled for a day. Its like its so full I can't squeeze it together. But that almost sounds impossible to me. There has always been some "air" or space in the system on each vehicle I've ever owned. How'd I manage this on this refill?



I opened the radiator, pulled the coolant level down to about an inch below the neck and will see what happens now.

 

[JLEONARD]

There has always been some "air" or space in the system

Well I don't think you want air in the system. That could get to a bad place in the enigne and form a steam pocket.



I know in boating there are vent lines at the high point to bleed out any air. Very important to bleed out all air. I did a nose down installation of a new Cummins 6B and there were specific things I had to change from standard to make sure the air bled out.



Is it possible the reason the hose is hard is because it is now holding 7 or 13 psi when your old cap held 0 pressure? Maybe time to do an old fashioned pressure check to know where you really are??

 

[Ncostello]

I agree air pockets are bad. I had a Mustang 302 once that was just a bear to get all the air out.



By lowering the radiator level to just below the absolute full point... it has now pulled in coolant from the bottle on its own. So its "taking" as much as it wants now.



I don't know. I'll try a pressure check to see whats going on. All I know is that on any vehicle I ever owned... I could always collapse the top hose with ease if it was stone cold. This one held some "pressure". Now its what I consider normal. I'll keep adding coolant to the overflow and see what it does on its own.