Coolant system has back pressure

[dave01]

my c8 has a lot of back pressure in the coolant system, i have flushed the system and replaced the thermostat, hope someone has any ideas please what it could be

[wheeler]

Do you have a bit more detail on what you mean?
What happens if you start the engine from cold with the coolant cap off & give it a rev?
Have you had the coolant checked for exhaust gasses?
How does the engine run? Is it overheating?

[Peter.N.]

Let the engine run for a while with the coolant cap removed and see if there are any bubbles, if so its likely that the head gasket is leaking I'm afraid. Head gasket failure does not of itself cause overheating but the pressure in the system blows coolant out via the overflow or filler cap, if it gets low enough then the engine overheats.

Check your coolant overflow bottle for coolant and look around the filler cap for traces of dried antifreeze.

Peter

[white exec]

my c8 has a lot of back pressure in the coolant system, i have flushed the system and replaced the thermostat, hope someone has any ideas please what it could be

Can you say what you mean by 'back pressure'?
It is normal for cooling systems to operate under pressure (up to around 1.4bar, when the pressure cap will lift).
As asked above, what problems/symptoms are you getting?

[GiveMeABreak]

Have a look at my post here and make sure you followed the procedure correctly:

viewtopic.php?p=601625#p601625

Although this is for the C5 X7, I have checked and it is identical to the C8 procedure in every detail. This includes the degassing procedure.