I have a 97 Silverado w/5.7 Vortec, 124000 miles, I have put 3 new 195 degree and 1- 210 degree thermostats, new water pump and can only get luke warm at best heat inside, from first start up temp will climb to 210 for a few seconds before dropping back to 160 degrees on instrument gauge, laser temp gauge shows close to right temp at thermosat housing and radiator hose. Any ideas?
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1997 Silverado NOT heating up.
- Thread starter loadmyown
- Start date
Bad temp sensor or bad display
My bad, just re-read your post. Either the heater core is clogged or the blend-door is stuck. Both will cause cooler air.
Try back flushing the heater core
I couldn’t get past 97 with 124k 
Heater core is stopped up or the mixer motor isn’t working correctly.
Measure the temp on the intake and output sides of the heater core. An infrared thermometer is the easiest. If it is flowing correctly, you likely have a blend door issue. My bet is in the heater core.
Just dealt with this on my '94 K1500, Heater core was completely clogged on mine. Pull the two hoses off the heater core and flush it backwards with a water hose into a bucket. IIRC one fitting was 5/8 and one was closer to 3/4. Even after a flush, new waterpump, thermostat, hoses, and sensors my truck only gets to around 175 but you could slow cook a turkey inside it.
These trucks had issues with the blend door. They can usually be pulled apart, cleaned and put back together.
Pretty much THIS.
Had the same issue with my 1998 S-10 last winter. It was blowing cold air even when set on the highest heat setting.
The heater core input hose was hot, but the output hose was stone cold.
I pulled both hoses and flushed them with a hose pipe. It looked like MUD flowing out at first.
I alternated spraying water in both hoses until everything ran crystal clear both ways.
I hooked everything back up, topped off my radiator and my heat works so well now that it’ll roast you out!
