heater issues

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

scrap--metal

Full Access Member
Joined
Sep 15, 2021
Posts
694
Reaction score
1,328
Location
MN
First Name
Calvin
Truck Year
'85, '81
Truck Model
K10, K20
Engine Size
305, 350

fender89

Junior Member
Joined
Feb 26, 2022
Posts
23
Reaction score
23
Location
Pacific Northwest
First Name
Randy
Truck Year
1985
Truck Model
k20
Engine Size
350
Hahah yes I assumed it was could of sworn it was cold when the engine was running. But at this point I'm not sure what else to check
 

fast 99

Full Access Member
Joined
Dec 31, 2021
Posts
2,097
Reaction score
3,079
Location
Spokane, Washington
First Name
Brian
Truck Year
81,85
Truck Model
K20
Engine Size
350
If the core is out replace it with aluminum. They are much more efficient. I keep saying it one this site, buy a cheap heat gun. They cost around $20 today. It is really hard to diagnose a heater problem without some actual numbers like the temperature of thermostat housing, difference between inlet and outlet hose temps at core.
 

fender89

Junior Member
Joined
Feb 26, 2022
Posts
23
Reaction score
23
Location
Pacific Northwest
First Name
Randy
Truck Year
1985
Truck Model
k20
Engine Size
350
Well.... I think I found the problem the thermostat was stuck open ... Thank you to 85k30 even tho I didn't take the advice initially..I had just replaced the thermostat about a year ago. I also could of sworn I felt the upper rad hose was cold after the truck had been running a while but I guess not. Anyway thanks for the advice fellas
 

SquareRoot

Full Access Member
Joined
Mar 18, 2017
Posts
4,232
Reaction score
8,132
Location
Arizona
First Name
Mike
Truck Year
85
Truck Model
K20
Engine Size
350
so now that its -15 out i guess i need heat. only blowing lukewarm out of vents. i checked coolant levels are good. top of the radiator. both hoses running to the core are hot. i took them off today and flushed out both ways. still not blowing anything but lukewarm. from my understanding its a super simple design, hot coolant flows thru a radiatior, fan blows over it and creates heat. if when i flush it comes out both ways just fine where is the problem?Yo
Your location says central AZ and it's -15? Damn!
 

Camar068

Supporting Member
Supporting Member
Joined
Feb 5, 2014
Posts
4,348
Reaction score
3,426
Location
Kentucky
First Name
David
Truck Year
1986
Truck Model
K10/LM7 5.3/4L60e/np208/3.73/32"
Engine Size
10 yrs Air Force
Well.... I think I found the problem the thermostat was stuck open ... Thank you to 85k30 even tho I didn't take the advice initially..I had just replaced the thermostat about a year ago. I also could of sworn I felt the upper rad hose was cold after the truck had been running a while but I guess not. Anyway thanks for the advice fellas
Good info, didn't know that. TY @85K304SPD as well. lol if I did know it, dun forgot.
 

85K304SPD

Full Access Member
Joined
Mar 29, 2022
Posts
475
Reaction score
707
Location
Las Cruces, NM
First Name
Richard
Truck Year
1985
Truck Model
K30
Engine Size
402
I had this happen one time with one of those "fail safe" thermostats in my Jeep, on a deer hunting trip. The thermostat got locked in the open position, and it never got hot enough to heat the heater core up. No more of those "fail safe" in any of my vehicles.
 

potent rodent

Full Access Member
Joined
Mar 22, 2020
Posts
195
Reaction score
112
Location
indiana
First Name
butch
Truck Year
86 and 78
Truck Model
1500
Engine Size
350 and 305
how did u test it did u take it out and put it in a panof boiling water an see if it open up ?
 

GARY l

Junior Member
Joined
Jan 5, 2024
Posts
3
Reaction score
0
Location
USA
First Name
Gary
Truck Year
1987
Truck Model
1500
Engine Size
350
so now that its -15 out i guess i need heat. only blowing lukewarm out of vents. i checked coolant levels are good. top of the radiator. both hoses running to the core are hot. i took them off today and flushed out both ways. still not blowing anything but lukewarm. from my understanding its a super simple design, hot coolant flows thru a radiatior, fan blows over it and creates heat. if when i flush it comes out both ways just fine where is the problem. I had the same problem it was a vacuum hose that wasn't plugged in.
 

GARY l

Junior Member
Joined
Jan 5, 2024
Posts
3
Reaction score
0
Location
USA
First Name
Gary
Truck Year
1987
Truck Model
1500
Engine Size
350
it's a vacuum issue, check the vacuum line that connects to your center actuator you'll find it just left of your floor vent up behind the duct it might be unplugged.
 

Latest posts

Forum statistics

Threads
44,449
Posts
958,190
Members
36,824
Latest member
rtomrdle
Top