Hi everyone... I have a 94 K Blazer. For some reason, it just doesn't warm up. I put a new 195 thermostat in it, and when I first start it up, the temp climbs to 195, the thermostat opens, the temp drops to about 140, but then never comes back up? I've ruled out heater core issues more or less, though not completely. It just doesn't make sense unless the new thermostat was bad. Could there be something else going on? Any input would be appreciated!!

 

As discussed in a few other topics on the 4.3L with similar issues, this is a result of having air in the system. Try elevating the front of the truck with the passenger side slightly higher than the driver side. Run the engine up to operating temperature with the radiator cap off. Then let it cool down to ambient temp. Do this several times, attempting to keep the radiator as full as necessary (so as not to allow air back into the engine).

 

I thought I purged all the air out already, but it may be worth another try. Right now the radiator level is right to the top, and the overflow is right where it should be. The other thing that strikes me is that with the cap off and the engine running, I can see a big change in fluid level inside the radiator when I give it gas and raise the rpm's. The water goes way down for some reason. I topped it off and capped it last time when the level was at its lowest, but my temp gauge still only reads about 140 after the thermostat opens, and I'm not getting much heat at all from the heater. Is there something that could be causing a vacumm inside the system that works to hold open the thermostat? It's just not making sense.....