I need your help Bricksters. I am still trying to track down the problem of an overheating B21 engine in a 1976 245 project car. I took the radiator out and had it cleaned internally by a shop. New thermostat. New temperature sensor. Bentley's troubleshooting of the guage checks out ok: when wire grounded, guage pegs hot, connected to a 68 ohm resistor it reads about 3/4 or slightly higher.

With the thermostat out, the car runs pretty cool, barely into the green. With the thermostat in, guage runs right up to and just into the red. This is a new thermostat(88 deg. C), and it opens fine when heated on the stovetop.

The previous owner had neglected the cooling system, running the engine without a thermostat or changing the coolant which was horrible looking. Looked like rustly water possible greyish, not green at all.

So what's left to do? I am assuming the water pump is circulating water because with the thermostat out the engine stays cool. Am I looking at a blown head gasket? I get some steam out the tailpipe with thermostat in and engine running hot, but running cool with no thermostat no steam present. Idle quality is ok, considering condition of motor mounts.

How can I tell if combustion gas is getting into the coolant and would this overheat the engine quickly?

Thanks in advance,

HighMiles