Hey all, Im new to the forum and have been searching but unable to find anything. I just inherited a 2000 Ranger 4.0 4x4 and it runs great. The only issue Im having so far is with the heat.
On the low and medium setting it blows heat fine once the truck reaches operating temp, however if I put the heat on the highest setting, it will blow out cold air. Im stumped - I was thinking about changing the heater core tomorrow before winter hits but wanted to ask before I rip out the dash if there is anything else I should check?

I dont have any water on floorboard, no coolant lose, no overheating, no other obvious signs of heater core leaking or failure.

Thanks in advance.

 

Welcome to the forum

Wouldn't be heater core if air is hot with medium and doesn't slowly get cooler

After engine is fully warmed up let it idle and open the hood
Feel both heater hoses, one will be slightly hotter than the other, thats the IN from engine hose
Other hose will be only slightly cooler if heater core has good flow
Turn fan to High
Then feel hoses again if out hose is getting much cooler then yes, core is the problem.
You can try Back Flushing the core
Label IN and OUT for core
Remove hoses and use garden hose on OUT connection, this will push out any debris that maybe be clogging the core out the IN connection
Then reinstall hoses but REVERSE THEM, out hose on In and IN hose on Out, this should be done each time you change coolant, it Back flushes the core while you drive, doubles the life of a heater core.


Could be the Blend Door is changing positions when Fan is on HIGH
Blend door is operated by the Heat control, it is a door that routes Fan air thru or around heater core, it uses an electric motor to move the door