I had a Dodge van with a well worn 318. I had all kinds of issues, oil pressure, up and down, foaming. Switched to 20-50 Havoline and problems solved. Held pressure around 60psi, hot or cold. No foaming. She was a little hard starting in winter, but always did.
My dad runs farm stock tractor pulls. He had a fleet of old gasser Olivers. He runs 15-40 Rotella in all of them. BTW-He's been a New Holland and White mechanic for over 40 years.
The stovebolts are built just like old tractor motors too.
