Possible clogged heater core, I just fixed mine by doing two things.

1. Back flushed the core (only) with a garden hose, hooked up to both sides first the outlet side (to back flush) and then the inlet side to make sure that any blockage is washed out of the core...make sure that the water runs clear both ways to make sure the clog is gone....

2. Replaced thermostat with new 195* since the gauge was not going up to the recomended heat range for the truck.

It now warms up quicker and I have heat early in the morning...

 

Thanks, What is the recommended temp? my gauge never goes above 140. Do you know where I can eg ta diagram of the engine as I do not know where to locate the heater core or the themostat, SORRY

 

Stock t-stat should be 195*F. If you aren't going above 140*F, then either your guage is bad, or your t-stat is stuck open. I would do a good coolant flush and install a new t-stat and radiator cap at the same time. New stat makes sure that it will run at the proper temperature and the new cap is just cheap insurance to keep the proper pressure inside the radiator.

 

read this.....fixed my problem long story short clogged heater core, letting some fluid pass......not enough to heat the air though
https://blazerforum.com/m_14360/tm.htm