Truck to Cold

[truckin 79]

Anyone else run into this problem, the 79 350 has a 4 core radiator undetermined thermostat. The truck can sit and idle for 20 minutes and heater gets a little warm but not hot. I was going to swap thermostat to 195 but just have not got around to it. The truck has a brand new aluminium heater core. My dad has had to borrow 79 because his truck is in shop and it has been cold in CO the last week, he has been freezing in truck. Is changing thermostat going to make a big difference? I am not sure if temp gauge is working but the thing barely moves off of C when driving around. I know it can be a bad thing if engine runs to cold

[Richard2112]

I am dealing with a similar circumstance. Though I haven't played with my radiator, I did r/r my carb and manifold, put new plugs in. Now the temp wont go into the "normal" range. I may have installed a colder plug and may have coolant leaking past the thermostat. I used rtv on the t-stat gasket and surfaces. Maybe I shouldn't have done that. Gonna change out the t-stat and put the old plugs back in to see which one makes the biggest difference.

[Dead Parrot]

Spark plug temp range has little to do with coolant temp. For most stock SBC motors, a 195 is the OEM temp for tstats.

Yes, if the installed tstat is a 160, changing to a 195 makes a big difference in heater temps.

The other thing to check is to make sure your heater core is getting coolant from the intake manifold port and returning to either the water pump or radiator. Some folks will connect the heater core to both the pump and radiator. Won't get much flow that way.

[Richard2112]

Originally Posted by Dead Parrot

Spark plug temp range has little to do with coolant temp. For most stock SBC motors, a 195 is the OEM temp for tstats.

Yes, if the installed tstat is a 160, changing to a 195 makes a big difference in heater temps.

The other thing to check is to make sure your heater core is getting coolant from the intake manifold port and returning to either the water pump or radiator. Some folks will connect the heater core to both the pump and radiator. Won't get much flow that way.

Thank you Dead Parrot. That sorta narrows my work load on an otherwise overtaxed schedule. I'll change out my t-stat (when I get an opportunity) even though it was working before I removed it, doesn't seem to work now.

[sweetk30]

seen lots of t-stats go weak and open /close way early and little to no heat . there cheep so swap in a new one .

also use a IR temp gun if you have one and check the temp at the t-stat housing and watch it cycle . i have found lots of them this way .

and also check both heater hoses with the IR temp gun to verify flow or pluged system .

[tucsonjwt]

You might also try the scientific method - grab the heater hoses and see if one or both are hot and if you can sense coolant flowing through them. Also, in sub-freezing temperatures a piece of cardboard in front of the radiator might help, either partially or fully blocking it, 18 wheeler style. Of course, you would not want to use the cardboard trick if the engine temp gauge started rising rapidly.

[homemade87]

I used to use the cardboard trick on my 82 when I was working out of it . About half of the radiator . Worked good . I had no other problems . It was a tbi system I had on it . Also if an engine is running a little on the rich side it will run cooler . The cardboard could give you what you need .


Also be sure to check your blend door operation . Could be it is not switching over completely .

[Fred n' Ethel]

Originally Posted by truckin 79

Anyone else run into this problem, the 79 350 has a 4 core radiator undetermined thermostat. The truck can sit and idle for 20 minutes and heater gets a little warm but not hot. I was going to swap thermostat to 195 but just have not got around to it. The truck has a brand new aluminium heater core. My dad has had to borrow 79 because his truck is in shop and it has been cold in CO the last week, he has been freezing in truck. Is changing thermostat going to make a big difference? I am not sure if temp gauge is working but the thing barely moves off of C when driving around. I know it can be a bad thing if engine runs to cold

I had a 79 K20 4wd manual.
What you describe fits the description of a low coolant level.
On mine, the heater blowing "cool" was the first indicator.
Needed a properly functioning radiator cap and overflow/recovery tank.
Totally fixed mine.
FWIW.