No Heat? (Seems Simple)

Hello Everyone,
I have a 97 Express with a 4.3. In November, I noticed very little heat was coming from the vents. First thing I figured was the heater core. Checked it, OK. I noticed the engine temperature was only going upto the second large line on the temperature gauge (the one between 100 and 210 - there's no number). Must be the thermostat. Bought a new one, flushed the system, new coolant. No change. The air door for the heater core moves, so I know its not that. I then checked the heater core hoses and the upper and lower hoses, they do not get that hot. I use the van daily, as well as driving approximately 300 miles each way every few weeks to get my son from college (just did it this weekend), and the engine temperature does not rise above that line. I believe the gauge and sensor are working because the hoses do not get hot. I also do not believe that there is an issue with the heater control valve because of the hose temperature. Any ideas? Thanks for any help.

Hello Everyone,
I have a 97 Express with a 4.3. In November, I noticed very little heat was coming from the vents. First thing I figured was the heater core. Checked it, OK. I noticed the engine temperature was only going up to the second large line on the temperature gauge (the one between 100 and 210 - there's no number). Must be the thermostat. Bought a new one, flushed the system, new coolant. No change. The air door for the heater core moves, so I know its not that. I then checked the heater core hoses and the upper and lower hoses, they do not get that hot. I use the van daily, as well as driving approximately 300 miles each way every few weeks to get my son from college (just did it this weekend), and the engine temperature does not rise above that line. I believe the gauge and sensor are working because the hoses do not get hot. I also do not believe that there is an issue with the heater control valve because of the hose temperature. Any ideas? Thanks for any help.

If heater hose does not get hot to touch the heater core is plugged or engine is not getting up to running temperature 195 degrees.
Check engine running tempt with a digital thermometer.
if 195 degrees remove heater hoses and see if you can blow air threw heater core.
Or remove return hose and stick it into radiator filler top.

Thanks MT-2500. The core is not clogged, fluid runs through it. I did the air test, air flows through it. I checked the temperature of each hose when I got home from work (a few minutes ago, I have about a 25 minute commute). Upper - 165, Lower - 151, core inlet - 154, core outlet - 154. I am assuming my issue is that the engine is not getting to running temperature.

Thanks MT-2500. The core is not clogged, fluid runs through it. I did the air test, air flows through it. I checked the temperature of each hose when I got home from work (a few minutes ago, I have about a 25 minute commute). Upper - 165, Lower - 151, core inlet - 154, core outlet - 154. I am assuming my issue is that the engine is not getting to running temperature.

I would try another thermostat.