[piecesparts]

I also hope that you are not experiencing anything big on this, however, my guess would be a head gasket failure on this truck. If it is a 305 engine, then there was a lot of them that experienced a crack in the heads that caused a lot of coolant leakage issues. Been there, experienced that. I removed my old 305 and put in a GM 350 in it's place many years ago and got many miles out of it, before I put ina stroker engine for more HP.