MrRusty

I got 94 F150 with 4.9L I6 couple days ago and the previous owner told me that there is no thermostat in the engine... Supposedly it was getting stuck so he removed it. Will running no thermostat hurt the engine?

I think I should put the thermostat back in so the engine reaches operating temperature, even though I live in AZ and its always hot here...

sylver91

Yes put the thermostat back in, check that the coolant isn't pure water which will likely cause sticky thermostats from corrosion. Without a thermostat the engine never gets up to temp properly and actually runs richer.

ymeski56

Yep. It will load up the combustion chambers w/ deposits & dramatically reduce the effective life of your Cat converters, from never reaching normal op temp, where the ECU enters close loop function & fuel trim occurs.

W/o the correct Thermostat. you will never come out of over-richened cold start mode.