Water temperature

[ERA 778]

If you've had the car for that long and never had to disturb the cooling system, it might be that just by coincidence the thermostat has decided to "retire" at the same time as the fan switch. Might be worth the trouble to go ahead and swap it.

Make sure you get the right replacement unit. I learned last week that I had the wrong one in mine - bought one for a 68-70 FE at first, needed it to be for a 63-64. The older ones are larger in diameter and correctly fit the recess in the expansion tank flange.

[jhv48]

If the fan coming on doesn't seem to effect the temperature, then your thermostat is defective.

When the water is hot, touch the radiator hoses. Are they good and hot too? If not, then the thermostat is not opening. Or, if warm, but not hot, then the thermostat has one or more 1/8 inch holes drilled in it that are letting some water flow though not enough to adequately cool the engine.

Do the air purge thing first. Then, if no change, replace the thermostat.