Quote Originally Posted by relyimah View Post
TD, I had a compression test done and it passed. And a sniff test or whatever it is. Also passed. Turned out head was cracked over 4 cylinders.
Had similar issues (pressure building overnight etc). May not be what you want to hear, but does sound familiar

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What does "holding residual pressure for a while after shut down" mean? Coolant not being sucked back into radiator as motor cools down?
Hate to say it but I also think it's sounding like either a cracked head or a cylinder head gasket blowing between cylinders. Given that it runs ok for 20kms or so before playing up I'd guess that the cracked cylinder head is more likely.