Head Gasket Mystery

[EthanMuh]

why hello, I'm an owner of a 1989 325i that I recently put a m20 with getrag tranny in. the issue is simple when I try to bleed the coolant system there is bubbles that have quite the magnitude surging from the funnel. This would be an easy indicator of a blown head gasket, pressure getting into the coolant from the crank. so I popped the valve cover and no milkshake and the top of the head looks super clean so I decided to drain the oil and to my surprise no coolant was in the oil either not much evidence of milkshake in sight. When i looked closer at the seam between the head and the block I could not find any residue signifying that any coolant was escaping. So before i crack the head off and ruin that magic im just wondering if anyone who knows a little more than me can help.

Could a crack in the head or damage between the cylinders cause these symptoms?

since it does not smoke on startup or idle only when its driven about 20-25 minutes what other possibilities am I looking at?

am i better off just getting a thicker head gasket and apr studs as i am going to turbo this year?

should I try anything else besides replace head gasket and inspect head surface?

just out of ideas lads, hope you guys can help a kid out.

Thankful for anyhelp you guys can provide!

[mbonder]

Do a compression test and a leak down test before you start tearing the engine apart. Share the results before doing anything else.