Radiator pressure

[BigRed94]

I have some questions about radiator pressure.
I have 2 1994 idi f250 one had pressure in the radiator system after 1-1/2 years of sitting and the other sat for 4 months and didn’t have any pressure in the radiator, both where checked before starting for the first time in a long time.
The one that kept the pressure is the truck I’m parting ways with.
Is there any issues with having a radiator not keep pressure. I’m afraid the truck Im keeping has a weaker engine.
I know the injection pump is going bad it doesn’t start nearly as quick as the other one. The other one fired up after 1-1/2 sitting like it was running everyday.
Sorry for the long post.

 

[BeastMaster]

Pressure in the radiator when cold? Bad news. All the water should have gone back to liquid state, and if anything, drawing a slight vacuum, which sucks additional coolant from your overflow tank back into your radiator, topping it off.

Keep your eyes on it for cavitation. It might be exhaust gases. Those do not condense.

 

[BigRed94]

Pressure in the radiator when cold? Bad news. All the water should have gone back to liquid state, and if anything, drawing a slight vacuum, which sucks additional coolant from your overflow tank back into your radiator, topping it off.

Keep your eyes on it for cavitation. It might be exhaust gases. Those do not condense.

Yes both engines were cold when the radiator cap was taken off.
So, the engine that help pressure might have cavitation and the engine that didn’t have pressure is normal?

 

[BigRed94]

Pressure in the radiator when cold? Bad news. All the water should have gone back to liquid state, and if anything, drawing a slight vacuum, which sucks additional coolant from your overflow tank back into your radiator, topping it off.

Keep your eyes on it for cavitation. It might be exhaust gases. Those do not condense.

Yes both engines were cold when the radiator cap was taken off.
So, the engine that held pressure might have cavitation and the engine that didn’t have pressure is normal?

 

[chillman88]

Yes both engines were cold when the radiator cap was taken off.
So, the engine that held pressure might have cavitation and the engine that didn’t have pressure is normal?

How long were they sitting? Overnight and had pressure or weeks or?

 

[BigRed94]

How long were they sitting? Overnight and had pressure or weeks or?

The one that had pressure sat for 1 year plus.

the one that didn’t hiss sat for 6 months.

I just notice the differences.

 

[aggiediesel01]

Cavitation is a bi-directional occurrence, compression can go into the water jacket but when the compression is gone, the water goes the other way. That usually results in stuck/hydrolocked pistons or lots of water in the oil, especially after sitting that long. If the truck started and ran fine then I wouldn't be concerned with cavitation yet. If both trucks started fine and don't have significant leaks then probably isn't anything wrong with either one. Maybe one of the radiator caps is bad? Maybe a water pump seal is weaker than the other? After running both with the radiator caps off long enough for the thermostats to open and water to circulate, shut them down and monitor the tops of the radiator fluid for an oil film or black carbon streaks laying on top of the fluid. Black carbon streaks would be from combustion gasses and oil film would be from leaking oil cooler. If it's nice and green then you're probably good to go. Maybe pressure test the caps and cooling system and if they pass, get on down the road.

 

[Philip1]

Its possible the pressure you noticed could have been caused by changing ambient temperatures too. I have an old truck that just sits for the last few years and every so often I would check the coolant in it and without running at all it built a small amount of pressure to cause it to hiss when opening the cap.

 

[Christian9112]

My cap was hissing before and thought it was normal. I noticed that the area around the cap would get hard water stains around it, like the cap was leaking coolant. I did a coolant flush and found out that the reserve tank nipple was clogged with dirt. I tried blowing air through the reservoir tank and nothing would come out. I had to drill out the clog and no more hissing. No more leaking.

 

[BeastMaster]

About the cavitation...

If I suspected exhaust gases are being forced into the coolant via pinhole leak, I would want to run another hose to the overflow port at the top of the radiator, and run it to a jug of water, so I could check for bubbling. And sniffable.

Testing on a cold engine. I don't want to have to consider boiling hot coolant. I am interested in exhaust gases, not water vapor.

If it seems to bubble excessively, then I would probably spring for a test kit for a second opinion. They use a blue fluid ( I think it's methylene blue ) to detect exhaust gas. My own suspicion is they are detecting CO2 by it's acidification of the coolant. Carbonic acid. Same stuff that gives beer and sodapop it's feel.

https://www.cpsproducts.com/wp-content/uploads/99081870_comb-leak.pdf