I've got this unsolvable problem with my heater & need to solve it. I had a engine put in my 98 Blazer a while back, now that's it's -35 outside, my heater blows cool air only. When the outside air is warmer then heater blows warmer air - never ever hot!! New water pump, thermostat, heater core & blend door actuator cause earlier it had hot air only. My mechanic buddy can't fix it. I've read lots here but nothing seems to work. I did have an air lock but it's gone now. Both heater hoses are equal hot. I've spent lots now & can't afford much more so any suggestions would be truly grateful.
HELP!!!

 

do you have a temp gauge in the truck? is it getting to operating temperature? i would try flushing the heatercore. its possible that half or more of it is clogged and the hot water is just flowing through the open ports causing it to never have heat.

last time i had this happen it was because the thermostat was stuck open. did you change it yourself? wonder if its possible its just a bad thermostat or if you brought it somewhere they didnt put it in

 

The hoses that go into the heater core, is the left hose warm/hot and the right hose cold/colder?

 

High temperature drop = low flow, reverse flush the core.

 

did you say the core was new?

 

I am suprised to hear of the issue with a new heater core...I say flush her out real good just to make sure there is no debris in there. Also is the therostat stuck in open position (fail safe)?

 

thanks for responding
left side is hot right side is a little cooler

yup ...sure is!

 

the thermostat helps maintain optimum engine temperature
If the thermostat is opening early or failing it is going to flow the rad to soon or to much
I would likely run a 195 thermostat and usually the temp is stamped on the thermostat
Any chance you guys put the thermostat in backwards ?

Another thing I would look at is the rad fan clutch
Usually a locked up fan clutch makes a lot of noise and drops your fuel economy and at -35 you dont want much fan LOL

I would be tempted to put a piece of cardboard in front of the grill and see if it helps just keep an eye on engine operating temps

 

My '00 Jimmy is having a heat issue as well. Regular heat doesn't work so I have to use circulation mode to get any heat. It works great on that mode but it switches off automatically after 5 minutes so I have to keep pressing it which is getting annoying. My mechanic thinks the heater core is blocked, he said that the s-10 series had problems regarding this issue.

 

three thing, can cause this, the hot and cold switch . actuator on passenger side, not letting the flap open all the way, or bad thremostat ,clog heater core if bith side of heater core is hot it a switch or actuator good luck ie under the glove box easy to get to if you dont mind small spaces and scratching you hand a little