Aside from a failed/ failing head gasket and thermal expansion what else can cause the cooling system to pressurize beyond the normal range of pressure?

 

Looking for a little help

 

failed egr cooler. failed cap, external leak, failed t-stat, failed vdf, failed belt or belt tensioner.
Im sure im missing something but thats a start.

 

Failed vdf? What's that is it near the harmoinc resonator too?

 

vdf= viscous drive fan.
just a fancy way to say fan clutch.

 

Looks like everthing was listed except for a bad radiator , and engine timing.

 

Paxdad -

One thing to keep in mind is that you asked about what could cause over-pressuring (past the normal range of 16 psig) BESIDES thermal expansion and bad head gaskets.

Certainly a bad EGR cooler could, but I need to think awhile on the other listed causes of overheating/puking. Many of them are ways to overheat. When you overheat, you get excessive thermal expansion, so in theory, I would think that these are just more forms of thermal expansion. One exception is adding enough heat to boil the coolant (surface boiling) and not re-condense it in the flow of coolant. This will not happen unless the coolant is severely diluted (ie just water) or you are severely overheating (which should be evident by losing power as I believe that the engine defuels at temps below these extremes).

I believe that popping the pressure relief (degas cap) can come from non-condensibles (head gaskets or EGR cooler), liquid expansion (lots of causes to add excessive heat), boiling (unlikely if your coolant strength is at 50/50 unless there is extreme overheating), or a weak cap/bottle. All other issues are forms of these four.

As always - I am certainly open to other perspectives!

 

Thanks for the replies! This certainly helps me to easily rule out several items. I can live with the failing EGR but hopefully it is not the head gaskets for a third time!!!!!