Is it normal for the cooling system to be under a significant amount more of pressure when the heat is off vs when the heat is on.

When i turn my heat off pressure builds in the hoses . I can squeeze them but they are definitely tight. If i run the heat for even a few minutes it feels as if there is hardly any pressure in them at all.

I should mention, Im running the Mishimoto thermostat, radiator and hoses and the 1.3 bar Mishimoto cap.

 

You should always be able to squeeze your hoses. They should never be under so much pressure it's rock hard.

But the reason could be because with the heat on it opens a secondary system which goes to the heat. But I would assume both on of off should be the same amount of pressure. You might have a blockage some where.

Maybe someone else can advise you better but I don't see why one would be under much more pressure.

 

agree...your water pump will make ~10-12 psi of pressure in the cooling system and if you're hoses are significantly harder than what 10psi would feel like that means you have alternate sources of pressure ... i.e. leaking head gaskets...not saying your HG are leaking but prepare yourself