Radiator under pressure when cold (2 Viewers)

[Willard]

So here is the dilemma the radiator under pressure when cold. When I say cold, the rig has sat for 4 months without been run.

What I know has been done in the last 5000-15000 miles
Rebuilt motor (5000)
Rebuilt head (15000)
Water Pump (15000)
Thermostat (5000)
Head gasket (5000)
Radiator (500)
Used cap (500)
Upper and lower hoses (other replaced in last 25000) (500)
Replaced rear heater lines and core (500)

Nothing is going into the overflow tank as it is dry as a bone.

Any clues? It has been years since I had to diagnose this.

 

[CaptClose]

Give the top and bottom radiator hose a squeeze, are they both under pressure? If I had to guess, you have a blockage somewhere. If I had to guess some more, I'd say the thermostat is stuck in the closed position. I've also heard of blown head gaskets causing this issue. But check the easy stuff first.

 

[NeverGiveUpYota]

And if there's nothing then are you absolutely sure the system is full? And I can't help but be curious why you think the radiator is under pressure when cold? Can you open the cap?

 

[Spike Strip]

Check for Hydrocarbons in the coolant to see if it's a head gasket issue.

https://www.amazon.com/Lisle-75500-Combustion-Leak-Detector/dp/B0007ZDRUI

 

[pithicus]

Does it pressurize instantly when started? If so that could be a head gasket issue.
But as mentioned check the thermostat first.
One thing that happened to my 3f that is probably very rare. My cooling system pressurized instantly when cold, had bubbles in the coolant.
Naturally assumed head crack or gasket.Replaced gasket [head was not cracked] Fired it up and exactly the same thing, pressure/bubbles in the coolant.
Turned out to be a crack in the propane converter and it was putting propane in the coolant. That was a very very frustrating experience.
If you run propane, , worth checking.

 

[Willard]

And if there's nothing then are you absolutely sure the system is full? And I can't help but be curious why you think the radiator is under pressure when cold? Can you open the cap?

Because after 4 months of sitting in my garage i opened the cap and rad fluid burst out.

Good news it is green as green gets.

 

[Willard]

I will have a look at the thermostat as this is the easiest check.
Nothing in the oil and nothing in the coolant. I have a feeling that the issue is either air or the thermostat. As the head gasket was just changed 5k ago, I would hate it if it was. I plan to pull the plug as well to see what is what. Nothing is leaking engine or radiator wise.

 

[pithicus]

Hopefully just an air pocket. I would run it with the rad cap off and watch for bubbles until the engine is up to normal operating temp. If the coolant bursts out like you mentioned and keeps spitting out, it might be something a bit more serious.

also, has the engine been overheated since the rebuild?

 

[pithicus]

I assume the pressure was there only after the engine was started....
After any air is purged/burped , if there is still instant pressure once starting a cold engine then it could be a more serious problem

 

[OSS]

Replace the radiator cap for starters, then see what happens next time. The cold pressure issue isn't caused by a faulty thermostat.

 

[Willard]

I assume the pressure was there only after the engine was started....
After any air is purged/burped , if there is still instant pressure once starting a cold engine then it could be a more serious problem

I am hoping not with the amount of work that has been done to this engine. I know from the previous owner that it was overheating and that is why he did the head first, then the whole engine and cooling system.
The very last thing that was done was the rear heater being rehooked up. I am starting to think it may be a air pocket.
I will try it without the cap and see if that helps and try to burp it.
Looking at the rear heater it was hooked up with hoses running the length.
The good news is it is not overheating.
Thanks everyone for the suggestions

 

[Willard]

BURP and I feel so much better. Had to force the air out of the rear heater lines.

 

[pithicus]

Excellent. Wish I had a happy ending when I had similar symptoms.