Water-in-oil on 251 motor

[DanPW]

Hi, My 251 motor in a 66 PowerWagon gets water in the oil, badly.  Just sitting, I get water into the oil pan.  The engine does run, and I get 85-95 psi dry compression in all the cylinders, and the plugs all look black, none seem to have been "steam cleaned".  So, from what I read, head gasket seems to be OK.  Besides a crack in the block, any other possibilities?  I have a 241 motor To swap in, but I'd like to keep the original if I can.  Thanks

[JBNeal]

maybe the head is not completely true, once everything cools off there might be a gap in the wrong place...examination of the head gasket could yield further evidence 

[Jeff Balazs]

Have you tried pressure testing the cooling system? Maybe put a tester on it and pump it up to 4# or 5# to see if it holds or drops quickly.

Putting a new head gasket on one of these flatheads is generally not too bad a job. There is plenty of info on this here on this site.

When I put my 230 together several years ago I used a Felpro gasket set. The head gasket failed about a year into using it. And yes a fair amount of water in the oil. It failed between #4 and #5 cylinders. I put a gasket on by Best and flushed the crankcase carefully and have not had any further problems.

Hth, Jeff

[NiftyFifty]

I’m ok with FelPro head gaskets, but in my opinion the spray copper gasket sealer is a must on these old trucks, I lost 2 gaskets in a row and my block was decked and head planed, so everything should be true, but as soon as I put the spray on I’ve been good