Blown head gasket or something else?

[Don-T]

I may or may not have a blown head gasket. I have conflicting information from the cooling system. Here is a list of what is going on, anyone have any thoughts on this issue? Thanks for the help!
There are a lot of bubbles coming up in the radiator when the engine is running.
When the radiator cap is on the system is pushing coolant into the overflow.
When the engine cools off it is not pulling coolant back into the system from the overflow.
Once the engine is cooled off overnight there is still pressure in the cooling system.
There is no smoke of any kind out the exhaust under any conditions.
The engine always runs at about 180* once it is warmed up.
When I bought the Blazer it had a 19 psi radiator cap. I just changed it to a 16 psi cap but I can't see that making a difference.
When I bought the truck the coolant looked new and after several hounded miles it still looks new.
There are no leaks anywhere on the engine, coolant or otherwise.
I did a combustion leak test a couple of times with a testor and it showed no combustion gas in the cooling system either time.
I wondered if the combustion detector was working so I tried it on the exhaust pipe. It changed very quickly to show combustion gas in the testor so I think it works.

 

[nyoffroad]

I think you have your answer but just don't believe it. The signs do NOT point to a head gasket.
I've seen healthy engines with bubbles in the rad= no problems.
Coolant expands when it gets hot, a full system will push coolant into the over flow tank and out of the tank if over full.
How do you know the system is not pulling coolant back in? If the system is full , it's full.
Truck doesn't smoke, no leaks and it runs at the proper temp and the test strip come up negative.
Sounds good to me.

 

[Don-T]

Sorry, I forgot to mention I did get the low coolant light a couple of houndred miles after topping it off with coolant when I bought the Blazer. That is how I initially discovered the concern.

 

[87cr250r]

That's exactly what my 6.2 was doing. It would push coolant into the reservoir when running but would hold pressure for months when the engine wasn't running. This kept it from pulling coolant from the reservoir. It ran this way for quite some time but gradually got worse. Disassembly revealed the failed head gasket. Meanwhile, I installed a 6.5 turbo engine and it's blowing bubbles in the coolant. It runs fine and is pulling coolant back from the reservoir. I plan to pull the crossover pipe in the future to identify which head is leaking.

 

[WWRD99]

Did the 19 lb rad cap pull coolant and not hold pressure?

Sent from my SM-S906U using Tapatalk

 

[MarkM]

If you suspect a head gasket leak then you need a product like below. It will let you know one way or the other. It looks for exhaust gases in the coolant. Hope this helps.

Mark

Exhaust gas tester

 

[Don-T]

Did the 19 lb rad cap pull coolant and not hold pressure?

Sent from my SM-S906U using Tapatalk

The 19 lb cap allowed coolant under pressure to go to the overflow bottle and never let the system to pull any back from the overflow.

 

[Don-T]

If you suspect a head gasket leak then you need a product like below. It will let you know one way or the other. It looks for exhaust gases in the coolant. Hope this helps.

Mark

Exhaust gas tester

View attachment 907119

This is the test kit I used and it did not show any exhaust gas in the cooling system. I wondered if the fluid was good so I tried it on the exhaust pipe and it quickly changed there so it seems to work.

 

[dougco1]

The 19 lb cap allowed coolant under pressure to go to the overflow bottle and never let the system to pull any back from the overflow.

Sounds like you have a cracked head.

It shows up when hot and running, putting your cooling system under pressure "crack expands open". When it cools down it tightens back up and holds your coolant system under pressure. IMHO

 

[Don-T]

Sounds like you have a cracked head.

It shows up when hot and running, putting your cooling system under pressure "crack expands open". When it cools down it tightens back up and holds your coolant system under pressure. IMHO

Unfortunately this makes a lot of sense. If the head is cracked, I guess nothing short of a replacement will fix it. I wonder how long it could last like it is.

 

[adf5565]

Unfortunately this makes a lot of sense. If the head is cracked, I guess nothing short of a replacement will fix it. I wonder how long it could last like it is.

I have both a set of 6.2 and almost new Promaxx 6.5 heads I’m looking to get rid of. If you’re interested send me a PM!

 

[87cr250r]

When you buy the test kits you have to buy a special fluid for diesel engines. They don't have less CO2 in their combustion products than gas engines.

With that said, the only time I have tried to use a kit was on a Cat 3512 that was blowing bubbles. The test never indicated anything. We used cylinder cutout to identify the head gasket failure.

On my 6.2 it had cracks in the main bearing webs so I wasn't going to waste any time diagnosing a HG failure.

 

[Don-T]

Sounds like you have a cracked head.

It shows up when hot and running, putting your cooling system under pressure "crack expands open". When it cools down it tightens back up and holds your coolant system under pressure. IMHO

Last night I ran the engine for a while so I could watch it. When started cold there were no bubbles coming up in the overflow tank. After about 4 minutes of warming up, the temperature gauge was coming up, the bubbles started to come up in the overflow. I am beginning to think you are correct in thinking I have a cracked head. There is no smoke at this time and the engine runs good. Anyone care to guess how long this may go on before getting much worse? Water in the cylinder, smoking, major loss of coolant, and so on. Might I go out to start it one day to find it is hydrolocked?

Does anyone know where I can buy a good rebuilt engine to replace this one? Anyone think I should just buy a set of heads and move on? The engine has just over 100k miles, or maybe just over 200k miles. When it reached 100k instead of showing 100k it went back to 0, the next digit in the odometer doesn’t seem to work.

 

[Don-T]

Does anyone know where I can buy a set of reliable rebuilt heads. I am keeping this stock, no power adders. I hope to use it as a daily driver getting good mileage.

 

[dougco1]

Does anyone know where I can buy a set of reliable rebuilt heads. I am keeping this stock, no power adders. I hope to use it as a daily driver getting good mileage.

Eastern Surplus has NOS fully dressed. Look under powertrain parts page 53. I bought a pair 5-6 years back and had no issues


HM-719 | Cylinder Head 6.2 Liter GM Diesel Engine HMMWV CUCV Chevrolet
6.2 Liter GM Diesel Cylinder Head for HMMWV and CUCV equipped with 6.2 Liter Diesel Engine
NSN #: 2815-01-265-7071, 2815-01-313-4309
Part #: 5742170, 10163712, 14071072, 10163712
Price: $519.00

 

[dougco1]

Eastern Surplus has NOS fully dressed. Look under powertrain parts page 53. I bought a pair 5-6 years back and had no issues

HM-719 | Cylinder Head 6.2 Liter GM Diesel Engine HMMWV CUCV Chevrolet
6.2 Liter GM Diesel Cylinder Head for HMMWV and CUCV equipped with 6.2 Liter Diesel Engine
NSN #: 2815-01-265-7071, 2815-01-313-4309
Part #: 5742170, 10163712, 14071072, 10163712
Price: $519.00

But, "before you pull the trigger", I would confirm that you have a cracked head/s or just need your head gaskets replaced first.

 

[Don-T]

But, "before you pull the trigger", I would confirm that you have a cracked head/s or just need your head gaskets replaced first.

Thanks for the info. I do plan to have my current heads checked before I buy new ones. At this point I am trying to decide if I want to do the work myself, or take it to a shop to get it done. My concern is I have not dealt with any shops around here that can do the work so I don’t know who to trust. I probably have all the tools I need to get it done but I am getting to that age my back doesn’t appreciate the heavy bent over work.

 

[Don-T]

When you buy the test kits you have to buy a special fluid for diesel engines. They don't have less CO2 in their combustion products than gas engines.

With that said, the only time I have tried to use a kit was on a Cat 3512 that was blowing bubbles. The test never indicated anything. We used cylinder cutout to identify the head gasket failure.

On my 6.2 it had cracks in the main bearing webs so I wasn't going to waste any time diagnosing a HG failure.

I bought a bottle of test fluid for diesel engines. It still doesn’t show combustion gas in the cooling system. I guess that doesn’t mean I don’t have combustion gas in the cooling system, it may just not be enough to show up yet.

 

[cucvmule]

If you decide to remove heads replacing the head bolts would be a GREAT idea. Arp makes replacements.

As for 6.2 cylinder heads all the used heads that I have ever looked at had cracks between the valves. Whether 1 cylinder or 4 at least 1 combustion chamber had a crack. Some are worse than others but when I see a crack I replace. I have also seen cracked cylinder bores, overheating is not recommended and will cripple the 6.2 in short order.

 

[Don-T]

If you decide to remove heads replacing the head bolts would be a GREAT idea. Arp makes replacements.

As for 6.2 cylinder heads all the used heads that I have ever looked at had cracks between the valves. Whether 1 cylinder or 4 at least 1 combustion chamber had a crack. Some are worse than others but when I see a crack I replace. I have also seen cracked cylinder bores, overheating is not recommended and will cripple the 6.2 in short order.

I will definitely scrap the head bolts in there now. I don’t know yet if I will get bolts or studs for it. I suspect the the studs are an unnecessary expense as the engine will not be modified.

It will be some time before I get to do this as I have a 73 K10 I need to get some things completed on first. I need to replace a broken rear sliding window, replace the doors, and rebuild the front Dana 44 axle.