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Discussion Starter · #1 ·
Like the tittle says :16 LML coolant do not go back to pressurized side when cool off.
the coolant stand in the middle
Of the pressurized side and do not pull back what is in the overflow when cool off. Top rad hose is soft in the morning, new thermostat and new coolant tank . ( weird is when I open tanks cap the level rise in the overflow side )
Help .
 

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Welcome to DieselPlace

Please tell us a little more about your LML ( Make, Model ) and list any mods.

(y)
 

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Usually the overflow side being full and pressure side low is a sign of a head gasket failing (or failed). Keep an eye out for coolant leaks, odor, and keep checking that radiator hose before cold starts.
 

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Before you do anything else. Go to the stealership and buy coolant sealer tabs. Be sure to ask if they were still used in this engine. I have no way to look it up. (Part number is 12378255 I believe) They will tell you how many you need. I think that it will be 3 packages or 15 tabs. You just put these in the radiator. I have seen many heads pulled when this is all you need. Virtually every GM product has used these since the Northstar engine came out. GM blames it on casting porosity.
 

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Wouldn't be the first LML that needed the tank replaced.
 

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It’s a month old 🤦🏼‍♂️
I would get a block gas tester and see if you are getting combustion gasses into the coolant system
 
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Would do this week end. I let you know .
As mentioned in post #5 ... suspected head gasket issue causing your tank /pressure issues
 

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Discussion Starter · #14 ·
As mentioned in post #5 ... suspected head gasket issue causing your tank /pressure issues
Just got the level back up and burp all the air, went for a 5 min spin a floor it a couple time and after the top rad hose still soft and level did not move.
i do a gas testto make sure.
 

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Before you do anything else. Go to the stealership and buy coolant sealer tabs. Be sure to ask if they were still used in this engine. I have no way to look it up. (Part number is 12378255 I believe) They will tell you how many you need. I think that it will be 3 packages or 15 tabs. You just put these in the radiator. I have seen many heads pulled when this is all you need. Virtually every GM product has used these since the Northstar engine came out. GM blames it on casting porosity.
I would argue that that’s the worst thing he can do, those tabs have a bad habit of plugging radiator and heater core passages. It’s a bandaid at best. Casting issues show up at low mileage because they are a manufacturing defect
 

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Did you replace the tank?
 

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Combustion test was negative.
do not know what else to do !
I have replaced a lot of head gaskets and never actually had the combustion gas test come up positive on a Duramax.

Keep monitoring coolant level, and for any under hood coolant odor. Some leaks on these trucks never produce a drip to the ground but can often be smelled instead.

Keep checking the upper hose on cold-starts, if there is a failed head gasket, it could be that the cylinder it’s failed on hasn’t yet been on the compression stroke when the engine shut down, causing it to not build that tell-tale pressure on the cooling system.
 
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