Kurtis2244

Ok...so I have no heat in the car and the temp guage is not moving even after having the car run long enough that it should go up in temp. I bought a new thermostat and before installing I tested both the old and the new and they both open at 195 as they should. I'm thinking that my temp guage or coolant temp sensor went bad AND my heater core went bad at the same time? Hmmm....coincedence? Any thoughts. It's an 86 2.8 liter mpfi

Awesome-X

The likelihood that both went "bad" at the same time is very slim. It sounds to me like you have a problem with your coolant system somewhere. A heater core doesn't really go bad. Get stopped up, or develop a leak yes, but neither of those things will cause your temp gauge to be so low. I think you should get an infared thermometer and see what's really going on. I don't know a whole lot about over-cooled cooling systems so hopefully another member will chime in.

Al Hasse

Can't help with the gauge since you've replaced the t-stat, which was my first guess. No heat could be a failed heater bypass valve, a vacuum operated piece that diverts coolant from the heater core when you have cool selected on the temp slider.

Looks something like this...

Kurtis2244

I'm not sure that I have that heater bypass valve you mentioned Al.....although the pic you posted looks familiar. I'll look for it.....whereabout might I find that valve? Also...what sensor is it that reads the engine temp and controls the temp gauge? I'd like to replace that and see if it fixes the temp gauge not reading.... So many darn sensors in these cars.....I do have an infared thermometer....where would you suggest I shoot temps on the engine and coolant lines to pinpoint better my problem?
Either way I guess two different problems have arisen in the car.

Awesome-X

The heater bypass valve will be on the passenger side and your heater core hoses will be connected to it if you have one. The sensor for the temp gauge should be on the drivers side in the side of the head, and I think it's only a 1 wire plug that should be green. I would point the infared thermometer at the upper and lower hoses, and the thermostat housing. Drive it around for a few minutes first and let us know the temps.

Kurtis2244

Thanks for that info. I will check that stuff tomorrow and let you know what I find out. I guess the temp gauge itself could have crapped out on me. If I change the temp sensor...I guess that will answer my question on that one.

ex-x-fire

When the engine is fully warmed up, you should not be able to hold the heater hoses very long. This will tell you if hot coolant is getting to the core.