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High pressure in cooling system

imiceman44

imiceman44

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So I am trying to button up my turbo diesel suburban and I put a new radiator in and I am having trouble with cooling system.
First I noticed that coolant is starting to puke out into the overflow tank a few minutes after starting a drive, left overnight it doesn't come back and pressure stays in the system and vents off when I open the cap, even 2 days later.
The radiator is hot on the upper hose coming in but not on the lower coming out until it pushed enough coolant out of the way.
I suspected combustion gases and tested at several stages, nothing, liquid is as clear blue as it comes out of the bottle.
The water pump has been making some tin rubbing noises and now leaks from the weep hole so I got a new one and will be replacing it, I also will be replacing the thermostat even though the hoses on both sides of the thermostat are same temperature, hot, I doubt it is stuck closed.
I hooked up a pressure gauge on the radiator and it started climbing once it warmed up and I had to stop it and release the pressure when it reached 25psi and climbing and it reached 28psi before it started to go down with the relief valve open.
To note both radiator and cap are new and the cap seems to hold the pressure until it gets above 13psi which is how it's supposed to.
I am stumped.
A head gasket would have made sense but no signs of that happening, oil is also still clean and clear after this happening over a couple of weeks and trying and testing.
The only thought I have now is that the water pump is falling apart and is not circulating the coolant and hot spots are forming on the cylinders and creating steam but would it build up that much pressure?
 
Sounds a lot like my 4th gen Camaro when it gets air trapped in the system. After being bled out - which is a monstrous task on these it stops.
 
Maybe I'm vastly oversimplifying what I am reading, but it sounds to me like you have a bad radiator cap.

Have you tried the old cap(?) which I presume worked ok?

Radiator caps are as bad as thermostats nowadays. Finding a good one out of the box is a day you should buy a lottery ticket. I run both used, until I know they have quit working.
 
dyeager535 said:
Maybe I'm vastly oversimplifying what I am reading, but it sounds to me like you have a bad radiator cap.

Have you tried the old cap(?) which I presume worked ok?

Radiator caps are as bad as thermostats nowadays. Finding a good one out of the box is a day you should buy a lottery ticket. I run both used, until I know they have quit working.
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Old cap leaked at the beginning, the new one opens up and allows the coolant to go to the overflow.
I just bought some fresh fluid to do once more the combustion gasses test
 
I think you are covering your bases but have not yet changed out the T-stat and pump?
Sounds like my old 350 that was in the blazer originally. It had combustion gases going into the system. It would puke coolant out of the bottle and pressurize the system. Hoses would stay hard for days :pimp: Everything cooling related was new. I didn't R&R the engine, just yanked it and built the 400. So yes, I'm guessing head gasket or crack for mine.
 
Just tested again, blue as it came from the bottle after a minute of something pushing through and bubbling up.
I just had to start with the bulb and it just kept going.
I will change the water pump and thermostat and see what happens and I will make sure I burp the system properly.
 
When I am suspicious of a gasket leak on a 6.2 or 6.5, I pull the belts so the water pump wont move, run the engine with the coolant crossover removed, with coolant up to the level of the port that you can see, it is obvious really quick if it is pumping air/combustion into the cooling system.
 
black dawg said:
When I am suspicious of a gasket leak on a 6.2 or 6.5, I pull the belts so the water pump wont move, run the engine with the coolant crossover removed, with coolant up to the level of the port that you can see, it is obvious really quick if it is pumping air/combustion into the cooling system.
Click to expand...
I will give that a try thanks
 
Those combustion leak testers don't work on diesels.
If you are getting up to 25-28 psi in the cooling system you have a head gasket leak,no way around it.
The pressure on the system after setting overnight is another dead giveaway.
 
black dawg said:
I have never had one of those test kits show positive on a diesel.
Click to expand...
I've probably caught 6 Duramax diesels with the test kit. We always let it run long enough to get some heat into it. The liquid turns green after pressing the bulb on the tester a few times if combustion gasses are present in the cooling system.

But the high pressure on the hoses and not going away are pretty good indicators of combustion pressure getting pushed into the cooling system like others have said.
 
ZooMad75 said:
I've probably caught 6 Duramax diesels with the test kit. We always let it run long enough to get some heat into it. The liquid turns green after pressing the bulb on the tester a few times if combustion gasses are present in the cooling system.

But the high pressure on the hoses and not going away are pretty good indicators of combustion pressure getting pushed into the cooling system like others have said.
Click to expand...
That's what is bothering me.
It has all the symptoms except it doesn't show with the test, and whatever was pushing kept going for a couple of minutes and the fluid stayed a perfect blue.
I just did the head gasket so I wonder if the head is not perfectly straight and I didn't use a thick gasket just a stock one.
I did follow procedure perfectly. :dunno:
 
Did you have the heads checked? I got burned on a dmax recently that I didn't get the heads checked and it ended up having a crack in the injector bore.
 
ZooMad75 said:
I've probably caught 6 Duramax diesels with the test kit. We always let it run long enough to get some heat into it. The liquid turns green after pressing the bulb on the tester a few times if combustion gasses are present in the cooling system.

But the high pressure on the hoses and not going away are pretty good indicators of combustion pressure getting pushed into the cooling system like others have said.
Click to expand...

What test kit are you using? I have always used the one from napa that says BLOCK TEST on the box.
 
black dawg said:
What test kit are you using? I have always used the one from napa that says BLOCK TEST on the box.
Click to expand...
Same one.
I even went and bought a new one since my kit was a couple of years old.
New liquid did the exact same thing, nothing.
The heads were previously rebuilt and had no problem other than swollen glow plugs from my stupidity.
Took the heads off to take care of that.
 
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