My '75Mercedes, inline 6, overheated one night in the middle of nowhere. I was't paying attention to the gauges and only looked when the engine started to sound rough.

I pulled over as soon as I could, looked under the hood, boy did it smell hot. I got it home. The engine had been so hot that it melted the insulation off the plug wires.

Then I got married and the car sat until I could afford to work on it. Letting it sit was a bad mistake. After four years I had enough money to rebuild the engine. I found a mess.
The burnt ethylene glycol ate pits in the cylinder walls, and the pistons were stuck in so tight that on two of them I had to pop the top off the piston and jack them out using a hollow core hydraulic jack and wire rope. The 100 ton jack had to work pretty hard to get those pistons out.

Later I found that there is a chemical called butyl cellusolve that might have made life easier.

Back to the block. I decided it needed "first oversize" pistons which are about 0.020 oversize, so I bought a set at $61 each from a gray marketeer. I was in an auto shop class then, so I bored the cylinders myself. That Mercedes cast iron is the best cast iron I have ever seen. Very hard, made the boring bar work.

I took the block to a local shop with a Sunnen automatic hone for final hone to fit and they did a nice job. However, when I got the block back into the shop I found that I could still see discoloration from the bottoms of the pits. But, I already had the pistons so I put the engine together and actually the pits didn't do any harm to performance.

Oh, yeah, cause of the overheating was a blown head gasket. The head when freed from the block was warped 0.024 on the exhaust side, less on the intake side. That was repaired by Arizona Cylinderhead, and a good job they did of straightening it out using an oven and hydraulic press. It only took a couple of thousandths milling to make it flat.

Moral of the story is, don't let the engine sit like that for any length of time! Or trade it for a good used one. I guarantee that it's going to need more than a head gasket.

R.