I still recommend a Cylinder leak down, Have seen good compression many times and still fail a leak down... But that is just me..

 

You can have a cracked head or gasket leak and have good compression. it's gas or water, figure that out and it answers a lot of questions.

 

X2 on what 440 said .....

 

I always check heads for straightness before re-assembling of an engine.
My reasoning is in case the block deck is out some, then the surfaced head and head gasket compression may seal properly.

Here is what I would do before engine disassembly (head removal):
remove your valve covers if a V-8, and with engine cold, loosen and re-torque all head bolts. I just replaced a broken head bolt in a '77 amc 304 V-8.
You could very well have a "stretched" head bolt which is not up to snuff, even tho your compression on each cylinder is close to spec. My cylinder's were too.

I was not getting white smoke, but around the 220 temp mark the broken head bolt would allow cylinder compression to aireate the coolant causing the temp to suddenly jump to 240 and Belch coolant. No over flow bottle at first, then installed overflow bottle and it didn't help a bit.

I was able to weld a nut and remove the broken head bolt very carefully with a cordless 1/2-inch impact gun (on third try).
The first two nuts twisted off using a long 1/2-inch breaker bar. The careful impacting broke the head bolt loose and out it came.
Now, for grins _ _ _ hahaha _ _ _ hill-billy mechanic-ing, _ _ _ I replaced the head bolt with a "new-used" pre-stretch bolt, and it is holding just fine.

When I was doing research on overheating, one of the pro-tech's said when all avenues have been exhausted, you have either a crack or stretched head bolts.

So, you might consider re-torquing the head bolts.

keep us posted and informed. and be patient if possible.

Good luck