CUCV Coolant Issue

[Curtisje]

I could spend the time digging through some 80s tech manuals I have, but I won't. I've been filling cars from this era and long before for over 30 years this way, and it works. Underfilling would be gallons...this is just a few quarts in a several gallon system. Letting the rad cap, in its set spring pressure, to set the coolant level is how it's done. If he had a blown head gasket, it wouldn't matter how he filled it. The upper hose would be under high pressure after a few minutes of running and over heating would occur, none of which is happening.

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If the cooling system is working properly the coolant level in the radiator will be at the neck/cap when you check it in the morning. If it's not he has a prblem.

I didn't say he had a blown head gasket, I just advised him to fill the radiator to the top and continue to look for the real problem.

I'm not trying to get in an argument about this. If anyone can show me GM or CUCV instructions that state anything different from what I have stated I will be grateful for learning something new, until then I will continue to advise based on my 40+ years of experience with GM trucks and the maintenance instructions associated with those trucks.

I'm here to help and understand we all have different opinions and experiences. Good luck.

 

[rsl0311usmc]

Brother you have a problem but underfilling your radiator will only cause more problems. An air pocket in the head may cause a cracked head.

If your radiator isn't pulling coolant from the overflow tank while it cools down after driving then it is pulling air in from somewhere else. That somewhere else spot is your problem.

Your coolant system is designed to be filled as I wrote above.

Do what you feel is best but I challenge you to find any GM or CUCV instructions that dictate not filling the radiator up to the neck/cap.

Semper Fi. Good luck.

Yeah after fixing the one leak I filled it up and once again I let it cool for a couple of hours and it's still a little high but I am hoping it comes down.

 

[rsl0311usmc]

If the cooling system is working properly the coolant level in the radiator will be at the neck/cap when you check it in the morning. If it's not he has a prblem.

I didn't say he had a blown head gasket, I just advised him to fill the radiator to the top and continue to look for the real problem.

I'm not trying to get in an argument about this. If anyone can show me GM or CUCV instructions that state anything different from what I have stated I will be grateful for learning something new, until then I will continue to advise based on my 40+ years of experience with GM trucks and the maintenance instructions associated with those trucks.

I'm here to help and understand we all have different opinions and experiences. Good luck.

Do you have any other ideas why it might be doing this? I tried it the other way to and lastnight it still pushed it into the overflow and stayed. It's weird though because if I don't drive it buy rev it till the thermostat opens a few hours later when it's cool it goes back down. But if I drive it it's a whole different story

 

[rsl0311usmc]

I am thinking of putting a new overflow hose on the truck with new clamps

 

[adf5565]

I would start with pressure testing the cooling system. My radiator runs full and uses the expansion tank as balance. Being that you’re blowing coolant out it sounds like something is pretty wrong.

Also have you emptied some of the coolant out of the radiator, leave off the radiator cap and start the engine? That can help with diagnosis.

Also, is it the factory radiator? Or aftermarket?

 

[Barrman]

Something to keep in mind is that the 6.2 diesel cooling system has around 4 gallons or 16 quarts of coolant in it. The stock thermostat is a 195° unit which starts to open at 192° and is fully open with full flow at 203°. The original post stated that there was a temperature gauge installed at the cylinder head but never stated if the temperature had gotten over 203°. Without a turbo, anything between 192° and 203° is considered “normal“ and not a problem.

However, even at normal temperature there can be several quarts to over a gallon of coolant expansion outside of the radiator if the radiator was full to begin with like it is supposed to be. As posted several time already in this thread, the radiator cap regulates the pressurized release of coolant and the vacuum powered return of the coolant to the radiator.

Water molecules are bigger than air molecules. Which means a small leak in the radiator neck, over flow hose to the over flow tank or the line inside the over flow tank could possibly not leak coolant but instead allow air into the system and stop the flow of coolant back to the radiator. Which will leave the overflow very full and the radiator low.

Yes, everyone thinks HEAD GASKET! With any coolant issue on a CUCV. Which it very well could be. A pressure test with a cold engine would be a very good idea. If everything seems ok start looking at more little stuff.

 

[rsl0311usmc]

Its a factory radiator and before with the cap off it just pushed it out

 

[rsl0311usmc]

Something to keep in mind is that the 6.2 diesel cooling system has around 4 gallons or 16 quarts of coolant in it. The stock thermostat is a 195° unit which starts to open at 192° and is fully open with full flow at 203°. The original post stated that there was a temperature gauge installed at the cylinder head but never stated if the temperature had gotten over 203°. Without a turbo, anything between 192° and 203° is considered “normal“ and not a problem.

However, even at normal temperature there can be several quarts to over a gallon of coolant expansion outside of the radiator if the radiator was full to begin with like it is supposed to be. As posted several time already in this thread, the radiator cap regulates the pressurized release of coolant and the vacuum powered return of the coolant to the radiator.

Water molecules are bigger than air molecules. Which means a small leak in the radiator neck, over flow hose to the over flow tank or the line inside the over flow tank could possibly not leak coolant but instead allow air into the system and stop the flow of coolant back to the radiator. Which will leave the overflow very full and the radiator low.

Yes, everyone thinks HEAD GASKET! With any coolant issue on a CUCV. Which it very well could be. A pressure test with a cold engine would be a very good idea. If everything seems ok start looking at more little stuff.

Alright will do that makes alot of sense also. I did order an oem thermostat (ac delco) to install after I get back from out of town. Thanks for all the information

 

[87cr250r]

Your head gasket is blown. I just went through this. When the engine is cold remove the radiator cap, start it, and watch for bubbles in the radiator. Bubbles means the head gasket is out.

This is your best scenario as head gaskets are cheap. Pull the heads with the exhaust manifolds installed. It's relatively easy in this truck. Torquing the driver's side head is difficult because your wrench will hit the brake booster bracket.

 

[rsl0311usmc]

Your head gasket is blown. I just went through this. When the engine is cold remove the radiator cap, start it, and watch for bubbles in the radiator. Bubbles means the head gasket is out.

This is your best scenario as head gaskets are cheap. Pull the heads with the exhaust manifolds installed. It's relatively easy in this truck. Torquing the driver's side head is difficult because your wrench will hit the brake booster bracket.

Yeah if tomorrow I walk out again and the fluid level is high in the overflow that's were I am leaning. I put a new overflow line on it and refuse to look at the level tonight as it's frustrating.

 

[Curtisje]

Do you have any other ideas why it might be doing this? I tried it the other way to and lastnight it still pushed it into the overflow and stayed. It's weird though because if I don't drive it buy rev it till the thermostat opens a few hours later when it's cool it goes back down. But if I drive it it's a whole different story

That is odd. I think replacing the overflow hose is a good and inexpensive attempt.

My only concern is that you may have a weak spot that allows air in the system while it cools down. Recheck all your hoses and connections. If anything is showing signs of dry rot or fatigue then replace it.

Another member recommended getting the radiator rodded. That would be good but that is basically rebuilding the radiator IF you have a shop nearby that does thst sort of work. It's getting hard to find good radiator shops.

Good luck.

 

[cucvrus]

My guess from afar is head gasket or cracked head.

 

[cucvrus]

I had this type of head gasket issue on several CUCV units. It will not heal itself. Expensive additives will not fix it. Remove the heads send them out to a good competent machine shop and do it right the first time. Don’t be surprised if it has cracks in the heads. It happens. Good Luck. No need for studs and hi performance parts it is 125 hp. Let it rip.

 

[rsl0311usmc]

So a quick update. I put a new overflow hose on late lastnight and filled the radiator all the way up and put the overflow at cold full. I just checked it and the radiator level is were I left it lastnight and it's only about an inch above cold full. I am hoping and it's looking like that hopefully that was the issue because as stated before it would stay way way higher and the fact the radiator is full is a good sign. Only time will tell

 

[rsl0311usmc]

View attachment 923697 I had this type of head gasket issue on several CUCV units. It will not heal itself. Expensive additives will not fix it. Remove the heads send them out to a good competent machine shop and do it right the first time. Don’t be surprised if it has cracks in the heads. It happens. Good Luck. No need for studs and hi performance parts it is 125 hp. Let it rip.

If what I did lastnight doesn't solve the issue I am in total agreement with you on the cracked head and head gasket

 

[cucvrus]

Hard top hose is the dead giveaway