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 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. Any ideas? Thanks for any help.

 

water pump? I would assume if that was the problem, it would overheat though.

 

It is either the control assembly..( the actual dash dial) or the heater control valve on the heater core.
If is the control dial, maybe you can test it, or bypass it to open the valve on the core....if its the valve itself...feel the two hoses going to the heater core...they should both be hot....if only one is hot..its the valve or the core is blocked...you could remove the hoses from the core, and flush out the heater core....
It could also be a connection problem between the two.