CUCV Coolant Issue

[rsl0311usmc]

Alright guys I got a new one for you and I need some advice. When I started working on this truck one of the first things I did was replace the coolant and thermostat because it was stuck open and I had no heat. Up till now it had been fine and running great and for the most part it does except for one issue. I also have a temp guage tied in on the drivers side block towards the front to monitor temperature. So lately I have been having coolant pushing from the radiator into the overflow tank and at one point overflowing it. The overflow tank becomes full and even when it cools off the level stays overfilled. Now if I pump it back into the radiator it goes back to the normal amount so the truck isn't burning it and it's not in my oil and I don't see oil in the coolant. I also don't smell exhaust coming out of the overflow tank while running. The truck seems to run great with the thermostat on my guage opening up around 180 to 190 then I notice the heat will also work. Now I have seen bubbles in the overflow tank while running and in the radiator before but I have also seen it not do it. The other day I started the truck with the radiator cap off and all it did was push a ton of coolant out. I worked the hoses and heater core hoses which were hot and thought I had discovered an air pocket because the coolant dropped and I filled it up and it seemed to not be bubbling to. Like I say though lastnight the low coolant light is now coming on and coolant is pushing into the overflow. The only thing I can think of is a head gasket or a cracked head or hopefully a faulty thermostat. The thermostat in there isn't an AC Delco and it's from one of the local stores. Also the truck doesnt overheat or exhibit the normal bad headgasket issues. Anyway any help would be really appreciated as always before I start putting money into it because I am currently having family issues costing my wife and I a fortune.

 

[WWRD99]

Alright guys I got a new one for you and I need some advice. When I started working on this truck one of the first things I did was replace the coolant and thermostat because it was stuck open and I had no heat. Up till now it had been fine and running great and for the most part it does except for one issue. I also have a temp guage tied in on the drivers side block towards the front to monitor temperature. So lately I have been having coolant pushing from the radiator into the overflow tank and at one point overflowing it. The overflow tank becomes full and even when it cools off the level stays overfilled. Now if I pump it back into the radiator it goes back to the normal amount so the truck isn't burning it and it's not in my oil and I don't see oil in the coolant. I also don't smell exhaust coming out of the overflow tank while running. The truck seems to run great with the thermostat on my guage opening up around 180 to 190 then I notice the heat will also work. Now I have seen bubbles in the overflow tank while running and in the radiator before but I have also seen it not do it. The other day I started the truck with the radiator cap off and all it did was push a ton of coolant out. I worked the hoses and heater core hoses which were hot and thought I had discovered an air pocket because the coolant dropped and I filled it up and it seemed to not be bubbling to. Like I say though lastnight the low coolant light is now coming on and coolant is pushing into the overflow. The only thing I can think of is a head gasket or a cracked head or hopefully a faulty thermostat. The thermostat in there isn't an AC Delco and it's from one of the local stores. Also the truck doesnt overheat or exhibit the normal bad headgasket issues. Anyway any help would be really appreciated as always before I start putting money into it because I am currently having family issues costing my wife and I a fortune.

I'd say get a new radiator cap on it. I can't remember the pressure though. I think 14.5...but I'd have to look that up. The fill point is a little above the heater core return.

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[NDT]

Get the radiator rodded out is my suggestion

 

[rsl0311usmc]

I'd say get a new radiator cap on it. I can't remember the pressure though. I think 14.5...but I'd have to look that up. The fill point is a little above the heater core return.

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I forgot to mention this is my second new cap. I put a nice new locking one on the other day. I believe the pressure is 15 or 16 and the cap is 16 psi. You think it's possible I am filling it up to much ?

 

[rsl0311usmc]

Get the radiator rodded out is my suggestion

Rodded out like flushing or cleaning it? There is your basic junk in it

 

[NDT]

A pro radiator shop will unsolder the tanks from the core and run rods through the tubes and remove the “basic junk” which plugs the flow.

 

[WWRD99]

I forgot to mention this is my second new cap. I put a nice new locking one on the other day. I believe the pressure is 15 or 16 and the cap is 16 psi. You think it's possible I am filling it up to much ?

Ok. I hate to assume either were good...but kinda have to. I have little faith in some parts stores. I'd look where the cap seals in the top of the radiator...see if it matches up with the cap seal and depth. Does the upper hose get tight still? And yes you can over fill it but the cap is the level regulator...if it's not working right it'll never get to pressure. I'd try to lower the amount in the radiator and overflow and see if it finds a balance. It should pull from the overflow keep filling it some until it stops pulling or pushing out antifreeze.

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[rsl0311usmc]

A pro radiator shop will unsolder the tanks from the core and run rods through the tubes and remove the “basic junk” which plugs the flow.

Ok I do have a replacement radiator. I had it because I knew they were hard to find in case one went bad. Maybe I can flush this one or just try replacing it.

 

[rsl0311usmc]

Ok. I hate to assume either were good...but kinda have to. I have little faith in some parts stores. I'd look where the cap seals in the top of the radiator...see if it matches up with the cap seal and depth. Does the upper hose get tight still? And yes you can over fill it but the cap is the level regulator...if it's not working right it'll never get to pressure. I'd try to lower the amount in the radiator and overflow and see if it finds a balance. It should pull from the overflow keep filling it some until it stops pulling or pushing out antifreeze.

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Yes the upper radiator hose gets pretty hard I won't lie like almost to much. I will check the cap and maybe get some pictures of the current amount in both. So your saying probably leave what's currently in the radiator and just fill the overflow till cold full and check it everyday till it stops pushing it back in? I will try to get photos here shortly of the current level. I forgot to mention I have been filling the radiator completely full like to the cap almost

 

[WWRD99]

Yes the upper radiator hose gets pretty hard I won't lie like almost to much. I will check the cap and maybe get some pictures of the current amount in both. So your saying probably leave what's currently in the radiator and just fill the overflow till cold full and check it everyday till it stops pushing it back in? I will try to get photos here shortly of the current level. I forgot to mention I have been filling the radiator completely full like to the cap almost

Oh ok there's your problem then...it needs room to expand. Gotta let it find its full. The cap does that. Since you fill it to the top it will push out the extra...explains the tight hoses too. Drop it 4 5 inches below the top and keep the over flow full to cold.

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[rsl0311usmc]

Oh ok there's your problem then...it needs room to expand. Gotta let it find its full. The cap does that. Since you fill it to the top it will push out the extra...explains the tight hoses too. Drop it 4 5 inches below the top and keep the over flow full to cold.

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Lol I guess I for some reason wasn't thinking when doing that. I saw the hole for the overflow when I had the radiator cap and told myself you shouldn't see fins in the radiator but then again when it expands it's gotta go somewhere like you are saying. So should I fill the radiator just a hair above the heater core hose on the passenger side then fill the resivor to cold full and drive it and see what happens later today? Also I probably wasn't having this issue in the winter because obviously it was colder and well now the weather is warm

 

[WWRD99]

Lol I guess I for some reason wasn't thinking when doing that. I saw the hole for the overflow when I had the radiator cap and told myself you shouldn't see fins in the radiator but then again when it expands it's gotta go somewhere like you are saying. So should I fill the radiator just a hair above the heater core hose on the passenger side then fill the resivor to cold full and drive it and see what happens later today? Also I probably wasn't having this issue in the winter because obviously it was colder and well now the weather is warm

Yup let the over flow fill it where it wants it. These do take a very long time to heat up. Not sure if you know but the other point of having the correct lb cap is to raise the boiling point of the coolant. Something to think about especially if you live in a high elevation.

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[rsl0311usmc]

Yup let the over flow fill it where it wants it. These do take a very long time to heat up. Not sure if you know but the other point of having the correct lb cap is to raise the boiling point of the coolant. Something to think about especially if you live in a high elevation.

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I really appreciate all the information. So I went out and cold filled the radiator just above the heater core line (few inches below top) and drained the overflow tank to cold full and ran her up to temp. I noticed this time I had heat getting warmer the entire time and the thermostat opened as normal. I checked everything the top radiator hose was soft and guess what the coolant in the overflow tank stayed right at cold full. I think that honestly was the issue and I will be driving it later to. Man do I feel like a dumba** ha ha and thanks again for all the help. I will let you know if it changes.

 

[WWRD99]

I really appreciate all the information. So I went out and cold filled the radiator just above the heater core line (few inches below top) and drained the overflow tank to cold full and ran her up to temp. I noticed this time I had heat getting warmer the entire time and the thermostat opened as normal. I checked everything the top radiator hose was soft and guess what the coolant in the overflow tank stayed right at cold full. I think that honestly was the issue and I will be driving it later to. Man do I feel like a dumba** ha ha and thanks again for all the help. I will let you know if it changes.

The over flow won't do much until you shut it off hot. It'll pull coolant into the radiator if it needs it...it takes a few drive cycles to get it leveled out then might see some move into it once it gets to be summer time heat then pull it back in once it cools off. The radiator cap is pretty important when it comes to how the coolant works in the engine. Just don't fill the radiator just the over flow unless it gets below that heater core return.

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[rsl0311usmc]

The over flow won't do much until you shut it off hot. It'll pull coolant into the radiator if it needs it...it takes a few drive cycles to get it leveled out then might see some move into it once it gets to be summer time heat then pull it back in once it cools off. The radiator cap is pretty important when it comes to how the coolant works in the engine. Just don't fill the radiator just the over flow unless it gets below that heater core return.

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Ok makes alot of sense. It's a very simple design and I was over thinking it. I am really glad it wasn't a head gasket issue. This is my favorite truck and I drive it everyday.

 

[Curtisje]

Lol I guess I for some reason wasn't thinking when doing that. I saw the hole for the overflow when I had the radiator cap and told myself you shouldn't see fins in the radiator but then again when it expands it's gotta go somewhere like you are saying. So should I fill the radiator just a hair above the heater core hose on the passenger side then fill the resivor to cold full and drive it and see what happens later today? Also I probably wasn't having this issue in the winter because obviously it was colder and well now the weather is warm

You shouldn't see fins in the radiator. When you remove the cap to check the radiator the water level should be up to the cap. Then your overflow tank should be filled to the FULL COLD mark.

You've got something going on but don't underfill the radiator as an attempt to correct this. Good luck.

 

[rsl0311usmc]

You shouldn't see fins in the radiator. When you remove the cap to check the radiator the water level should be up to the cap. Then your overflow tank should be filled to the FULL COLD mark.

You've got something going on but don't underfill the radiator as an attempt to correct this. Good luck.

Well then maybe it is some other issue then. I noticed yesterday after doing what the other member suggested that it was for the first time pulling coolant from the resivor back into the radiator which it was not doing before. Now I haven't checked it this morning but coming home lastnight climbing steep mountain roads that for a split second the low coolant light blimped on then immediately went off. So I am hoping my resivor isn't overfilled with coolant again. But I drove it twice yesterday and both times when it cooled off it pulled coolant back into the radiator and I only added coolant to the resivor up till cold full. I am doing what the other member suggested as to letting it find its balance.

 

[rsl0311usmc]

So I am out here messing with the truck and low and behold when I walked up to it I saw a new tiny quarter size spot in the driveway. This spot was on the frame below the heater core lines. The clamp on the top line appeared to be slightly loose. So I have tightened everything down filled her up completely and I am waiting to see what happens. But if I were to guess that may be the problem.

 

[Curtisje]

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.

 

[WWRD99]

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.

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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