Hi guys, Iv been running a built b18c4 with td05 turbo etc, put about 6000 miles on the setup and it's been awesome it just has an annoying problem, every now and again when your loading the motor up in 5th gear on the highway full boost full load etc itll blow some coolant into the expansion tank, sometimes more than other times, it sucks it back in eventually but if your on a long drive it can fill the bottle up, there's no way the heads lifting as it would be a mess at 20psi? I'm using arp head studs also tourqued down to 81ftlb. The problem doesn't really seem apparent in other gears or when under full boost in any other gear, Iv checked and tried everything. At the beginning I was fighting the temps rising under boost as there wasn't enough flow to the rad, the temps stay ok now, not great after a while of boost but hackable. Please people chime in with suggestions thanks.

 

I would think it's possible the Hg is leaking, multiple overheating events like you describe was probly too much for it?

Curious as to details of HG install.
OEM gasket?
Either or both gasket surfaces refinished?
Any spray sealant used?