A POS '01 2WD with 95k has been foisted upon me. Don't ask long story. It's not mine and I don't drive it. The lower hose blew off and it was parked before engine seizure. I replaced most cooling system components and flushed it out. Now it's got a new; water pump, fan hub, radiator hoses, radiator and cap. The thermostat is currently removed. There's no evidence of a blown headgasket. I have not done a compression or leakdown test.

Of course the lower radiator hose still blows off the radiator. Yes the clamp is properly tightened. I removed the first gasket on the radiator cap to vent it to the coolant overflow tank. Yes, I did check that the hose to the coolant tank from the radiator is clear and that the passageway in the tank is also clear. Now when the vehicle is parked after driving, some coolant will puke out of the coolant tank. I drilled a small vent hole in the overflow cap.

This makes me think there's some type of crack in the engine which is pressurizing the cooling system. Somewhere I read that is caused by a crack in the head by the exhaust valve. Does anyone have an idea what might be causing the pressurizing?

 

That is inconsistent with the rest of your post.

Everything you describe is "evidence of a blown head gasket."

Two tests, pick one.

Put a cooling system pressure tester on the radiator neck. Start the engine. If the system pressurizes as soon as it's running, before it even starts warming up, you have a blown head gasket.

A compression test will also let you know for certain.

 

I should have stated the usual signs of a blown headgasket. There is no; smoking or steaming from the exhaust, no milkshake looking oil or coolant, loss of power.

I did try the cooling system pressure test with an Autozone loaner tool. No results. I believe this vehicle has a very small leak that takes awhile to blow the hose off. It blows my mind that GM designs a vehicle that blows the hose off before the 16 psi cap bleeds the pressure off.

I'm skeptical that pulling the plugs and doing a compression or leakdown test will show anything. A pinhole leak is not going to bleed off much psi or %.

I don't have GM experience but plenty of shade tree mechanicing. What's puzzling is how it blows the hose after parking. Maybe because there's no electric fan to run once the engine is shut off. The other puzzling part is why don't air bubbles show up inside the radiator cap neck or coolant tank while running once warmed up?

 

While you had the Autozone cooling system pressure test kit, did you verify that the cap isn't seized up and holding much higher pressure than 16psi? I've seen them fail in a mode where they are solid caps. I don't care if it's new. I'm asking if you tested it and verified it's working right.

I've seen head gaskets fail only dumping pressure into the coolant system, without mixing oil and coolant. Lately, it seems like I've seen that more than oil involved gasket failures, especially in engines with Dexcool (and to some extent with other "long life" coolants). The coolant we use these days is really tough on gaskets.

It's possible that the gasket is opening up and dumping compression from one full cylinder as the engine cools down. I've seen all kinds of weird behavior from blown gaskets. I had a Dodge V8 a couple months back that would be sealed up and test good for compression and for the cooling system when the engine was cool, and would run fine right up until the thermostat opened. When the thermostat opened, all hell broke loose and it blew coolant out the overflow like a firehose.

 

No I did not test the cap. I will do that.

Another thing that is puzzling is that it will not have issues for many trips, then just randomly blow the hose off.

This POS has been severly neglected and might have the original plugs age welded into the heads. I'm a bit reluctant to try removing them an possibly kill a runner.

I've never tired the chemical solution for testing exhaust gasses in the coolant. How well do they work?

 

That is very consistent with my possible diagnosis:
I thought about going back yesterday and editing my previous post to point out that if that was happening, it would happen at most one time in six, and probably less than that. If the leak doesn't open under say 50psi (just making that up as a hypothetical), then the cylinder with the leak would have to stop high enough on the compression stroke to have over 50psi in it while the engine cools.

They work well to detect what they are designed to detect, but might not find an intermittent problem.

Those kits detect exhaust gases that are actively leaking through a bad head gasket. If the leak is fairly constant, you'll find it with that. If the leak only happens on cool-down and only with a certain cylinder at TDC, those kits will probably miss the leak. Even if you happen to have the test kit installed and checking at the instant of the leak, it's unlikely a "cool down" leak would leak any combustion products to vent through the radiator and the kit. The fluid won't change color if compressed air leaks through the radiator.

If you get one of those kits, look for ones with the little bulb pump mounted on the clear testing tube. The ones that use an external vacuum source are a PITA to use, unless you have 3 or 4 hands to hold everything, or unless you risk sucking coolant through the engine. Don't ever use the intake manifold as a vacuum source for testing the cooling system. It takes very little coolant through the engine and exhaust to destroy the catalyst and start throwing catalyst efficiency codes.

 

You could always try one of those "head gasket repair" in a bottle products. Bars Leak 1100 or CRC 401232 are two options.

When used exactly as the directions say, those can buy some time for an engine with a minor head gasket leak. They also claim to "fix" minor cracks in heads or blocks that leak compression into the cooling system. Follow the directions exactly, and plan on a head gasket job and a thorough cooling system flush in the near future.

I've actually used the CRC product on my own vehicle when I started having head gasket symptoms on a long trip and didn't want to deal with it until I returned home.

Unexplained loss of coolant, and unexplained hoses "blown off" are definitely symptoms of a failed head gasket leaking compression into the cooling system. It's not unusual for these symptoms (and the leaks that cause them) to be intermittent.

 

My condolences to you.

 

Those head gasket fixes in a bottle are bad news. They may seal your head gasket. They also seal your thermostat, coolant passages, heater cores, etc. I have seen it happen.

 

When misused, they can certainly cause problems. Hence my statement "When used exactly as the instructions say."

The best thing would be to fix the failed head gasket. That's certain.

If that's not an option, you can often by some time with the bottled head gasket fix stuff.

The first step for the one I used was to thoroughly flush all scale and rust from the system. Flush until it runs clean water out. That's so you don't "cement in" any problems.

The one I used (on an old Dodge 4 banger, not a GM engine) at least suggested removing the thermostat (if it didn't outright say to do that in the instructions). The OP Here says his problem vehicle is currently running with no thermostat, so that's not a problem for him either.

It also claimed to seal leaks in the heater core, but somewhat implied that if your heater core is good, you might want to bypass it. I'd recommend bypassing if your heat works, and the OP describes this vehicle as a POS, so it might already be bypassed.

OP also says he has a new radiator in this one, so there shouldn't be scale or blockage in the radiator. If OP wanted to be absolutely safe, maybe he still has the old radiator and could use that for the sealing steps. When I did mine, I had an older radiator, and immediately after using the stuff, I completely removed both radiator hoses and ran clear water through the radiator for a while to flush out any solution in the radiator. I let the water run while I pulled the drain plugs from the block to fully drain the solution from the block, and to let air in to cure the stuff.

Also, fuel or exhaust gases can interfere with the "head gasket repair in a bottle" stuff. So testing for that would be a good idea at first. With a conventional fuel rail, the recommendation is to disconnect the injector(s) and short the spark plug wire(s) to ground on any leaking cylinders (determined by compression test or coolant/corrosion on spark plug electrodes). Keeping fuel out of the leaking cylinder(s) on these engines would be much more difficult, so that might be a good reason not to even try this on a Vortec engine.