[Fot] Ever seen this one???

[Randall]

> Oil in the radiator WITHOUT oil in the water?

FWIW, I've got a similar symptom : oily residue on the cap but coolant looks
clean.  I believe it's actually the remains of some Barr's Leak (or similar)
that I put in in a vain attempt to stop the headgasket leak.  In spite of
both professional and amateur flushing, I still get oily brown gunk on the
cap.

> Had interesting overheating issue - runs fine 180-190 but 
> when I turn it 
> off, the water boils in the motor/radiator.

That can be a symptom of crud (including old stop leak) built up in the
bottom/back of the block.

> 50:50 prestone... 

Too much, IMO.  70:30 will provide better heat transfer and still protect
against corrosion (and freeze damage down to 0F or so).

> 4 lb cap. 
> Water goes into overflow bottle but does not appear to be pulled back 
> into the radiator when the engine cools.

I had exactly the same problem.  The special 4 lb caps don't seem to hold
vacuum properly, meaning that air gets sucked in through the center of the
cap, instead of drawing water uphill back from the bottle.  Could also be
sucking air through the water pump seal.

My solution was to have my radiator shop install a standard 3/4" fill neck,
so I could use a modern radiator cap.  I haven't actually installed a
recovery bottle yet, but I'm confident it will work when/if I do.

Randall