This is a '71 302 in a '73 F-100 with heavy duty radiator. I came out of a store a few days ago to see a lot of water leaking under the truck. Popped the hood to find a big bulge on the back side of the upper radiator tank, enough to have seperated the solder seal between the tank and the core. Got it home (1 block away) just as it started to really heat up, but before heat damage.

Well, I used radiator epoxy as a temporary fix on the radiator, and saucepan tested the relief valve in the cap, which worked fine. Then I checked fluids and found the oil almost empty! It was then that I discovered oil in the coolant and overflow tank, a lot of it. However, there is NO coolant in the oil!! I reverse flushed the cooling system until I had very clear water. I drove it around the block a few times until it got (fairly) hot again, and checked the coolant, which was once again milky brown. The last thing I did was look for bubbles in the radiator with the cap off and the engine idling. Yep, not a lot of bubbles, but they are there.

My guess is that the pressure from exhaust gasses and oil (which is under a lot more pressure then the coolant is) blew the upper radiator tank. This is almost certainly a blown head gasket, but it's interesting that the engine still runs great with no missing. Does anyone see something I might be missing here?