Hard upper radiator hose

[Yngdmax92]

Hey guys,

Diagnosing a Duramax recently and someone asked me wh going through coolant and a hard upper radiator hose in the morning indicates a failed head gasket or at least leans heavily towards that issue. My question is, I could explain help the truck uses coolant but I couldn't thoroughly explain the hard upper radiator hose as to why it they are suppose to check in the morning and see if the coolant system stays pressurized or builds more pressure over night
I always thought it was cause the specific cylinder the head gasket failed on which is #8 on this truck would be on the compression stroke when shut down and bleedomg the compression off over night.

Egr is deleted on this lml as well. So couldn't any body explain that a little more in depth please! Thanks!

 

[zakkb787]

Pretty much what you said if I understand it correctly. Head gasket isn’t sealing off cylinders from the water jackets, so cylinder pressure gets trapped into The water system. If I’m wrong mods can delete.

 

[Yngdmax92]

The response I received back from that Zak was that the static compression pushes past the rings, so how does it keep pressurizing the coolant system over night? That's something o I really didn't have a definitive anwser for

 

[JoshH]

Pressure in a cooling system is normally increased because of rising operating temperatures. As the system cools, this pressure will lessen, and there will be no pressure once the engine is totally cooled back down. When you have a failed head gasket, you are introducing pressure into the system via an outside source. When combustion gasses enter the cooling system, there is no way for them to escape unless you open the system. Because of this, they will hold pressure even when cold.

 

[Yngdmax92]

Damnit, wasn't thinking in that aspect. Thanks Josh;!!

 

[2004LB7]

I think maybe what he was getting at, is if the gasket failed then why doesn't the pressure go back into the cylinder and lower the pressure in the cooling system when it sits all night

If so, then I would say, because the combustion pressure is many orders of magnitude higher than the coolant system. It is this higher pressure that can get passed the gasket. But once in the coolant system then it slowly bleeds off through the cap keeping it at a steady 18 psi, or whatever the cap is rated for. When you shut off the engine the coolant cools off and retracts. And as Josh mentioned will lower the pressure. But with gas in the system that doesn't condense until much much colder. This is what helps to maintain the high pressure in the coolant.

And because the pressures are maintained at a relatively lower pressure then the combustion pressure, it cant flow back into the cylinder. The gasket is able to seal this out

My 0.2