Five years ago, I rebuilt a 390 to put in my 66 F-100. I had the heads reconditioned, and bought a used Offy aluminum intake for it. It still runs great, but now it seems there is oil mixed with the antifreeze in the radiator. There is no coolant in the oil pan though.
I had to replace the radiator last January, so I flushed the whole cooling system out until it looked clear.
It has a C-6 in it, and I was hoping the tranny fluid might have been leaking into the coolant with the old radiator, but the coolant is now a murky brown again with the new radiator.
I have yet to do a compression test, but I was hoping somebody has ran across this before, and might have some advice.
Great site, I have learned alot. Thanks.

 

Most of the time those symptoms lead to a cracked head or a blown head gasket. Some one else may have some more ideas but I thought I'd put in my 2 cents.

Brent

1969 F100 2wd

 

Sometimes the oil passage in the block that goes to the rockers develops a crack. It will leak oil into the water but not the other way around. You have to pull the heads off and sleeve the hole to fix this.

Also, the threaded hole in the head that the oils the rockers could have broken through into the water passage. That can happen if you use too long a bolt, forget the washer or just plain corrosion. Sometimes a thread sealer will fix this.

Barry

 

There are a number of little maybes to look at. The heater core: has the cooling system been filled with stop leak over the years? Maybe the new, fresh antifreeze (the type or strength?)has loosened something in the core and something is coming from the core. Pull off your oil fill cap. Is the underside wet or "foamy" looking? Water is getting in there from somewhere. I may be wrong, but if the water is just brown and murky, it probally isn't oil. Oil will not mix with water, should show up as a top film. Just some thoughts, good luck with it..

 

Yes, the underside of the oil fill cp is "foamy". The heater core hasn't been replaced, but I did add some stop leak to the old system, because the radiator was leaking.
The truck is in a relative's garage an hour's drive away, so I can't do much with it during the week.
This weekend I will run a compression test, and maybe pull the heads to have them magnafluxed.
I will keep you posted on what I find.
Thanks to all for the ideas, they are appreciated.

 

EDH,

My guess is head gasket. Drain the coolant before you loosen the head bolts. Look for rust trails accrost or underneath the gasket.

Jim