Driving a 98 F-150 Step-Side with a 4.2L-V6. Was troubleshooting an overheating problem that came out of nowhere and pulled the thermostat, didn't put it back in and ended up having to do a heater bypass. (I'm not proud of the half@$$ery under my hood, I was strapped for time and I'm just being honest.)

In it's current state the motor never really gets close to the normal temperature range.

Just how bad is it for my motor to be running so cool all the time?

 

Very bad. Depending upon how cool, the PCM may never switch to closed loop - and the truck will run rich, eventually peckering the cats, and washing down the cylinders, & contaminating the oil. Down on power, waste fuel, foul plugs, shorten the life of the O2's, Etc, Etc.... bad juju...

MGD

 

Thanks MGD! I was feeling pretty comfortable with it as a temp fix...now I'm kinda nervous having to drive it until the weekend before I can fix it. Hopefully just the thermostat brings things back to normal. I don't want to pull out my dash for the heater, electronics never act the same after that kind of removal for me.

 

Just replace the thermostat as soon as you can. You'll be ok then.
Bypassing the heater wont hurt anything.

Phil