'81 351W two barrel 2100 motorcraft carb. I bought this old PU a few months ago, and it runs just fine, but the motor heats up and diesels. Not always, but sometimes. I will be tuning it tomorrow thinking the heating up problem is due too advanced timing, because there is a new radiator on it. What else do you guys think could be wrong? It has a 13 pound radiator cap and the recovery tank seems to be working fine.

 

make sure there isnt any air. is the fan in decent shape? thermostat may be stuck. when does it start to overheat? could be the timing, running lean, head gasket, etc.

 

It is dieseling due to detonation. The first thing to check is the timing. Should be 10 degrees BTDC. With the vacuum hose off the distributor and plugged. Double check the thermostat. Someone could have put it in backwards. The "coned" end of the stat faces where the hose hooks to the housing. Make sure the coolant is mixed right also and no leaks.