I'd think if it were coolant it would be 1 or at most, 2 adjacent cylinders. If the head gasket was so bad that you were getting coolant into all 4, I'd think that you'd have other problems as well.

Maybe there's some sort of exhaust restriction on that side causing some backpressure and it to run super hot? IITC, you don't have cats though, so I'd think that's unlikely too....