The heater still won't work after I changed the thermostat on my

Service Manuals

https://www.google.com/search?q=1994+GMC+Sonoma+4.3+service+manual


How to Change A Heater Core on a 1994 GMC Jimmy, (Chevy ...

make sure all air is bleed from the system then check the heater hoses by touching them they should feel the same temperature if not then the heater core is plugged and needs replacing.

Possibly plugged or inerporable heater core. Possibly heater core valve (this diverts hot air through your heater system) When you flushed the block, was there a lot of contaminant? 95% of the time, cold heat means thermostat. Also there are a lot of really cheap after market thermostats, you can buy one as low as $6.00. That being said, just because a thermo is new doesn't necessarily mean it opens/shuts when it should. You can look on You Tube on how to test one in your kitchen with boiling water,.

So three basic things affect interior heat temps. Thermostat, plugged heater core/.valve, and insufficient coolant or liquid to tranfser heat. If your interior coolant (engine temp) is working normally and your vehicle reaches operating tempature according to the needle, your thermosat is probably not the cause.

My bet is somehow, your heater core is plugged so that their is not enough "flow"

Hello,,You may have to go to an after market supplier and pick up a winter front for the little guy,,or put a higher temp thermostat in,,good luck..

Check antifreeze level, if it's ok then it could be a problem with heater core

Follow the upper radiator hose. It will lead directly to the thermostat housing. THe housing should have 2 or 3 bolts on it. Remove them and then you will find the thermostat.

you should change the thermistat its probably stuck open

try topping the rad up ,if that doesnt work then pull one of the heater hoses off and bleed the heater

follow your basic instinct on this one ,thats how 99% of mechanics work

change the thermostat