Truck Runs Hotter When Heater is On?

[1990COTOY]

I have a '90 pickup with the 22R-E and it runs significantly hotter when the heater is on than when the heater is off. I changed the thermostat and flushed the cooling system but I still have the problem. I need help because this is completely backwards of what a heater usually does to the coolant temperature of an engine, and I'm out of ideas.

[bbagwell]

I am thinking maybe your heater core is plugged.

[clint marsh]

I am thinking maybe your heater core is plugged.
ditto

[1990COTOY]

Ok, ill check the heater core. Thanks for the reply.

[fourwd1]

On the 22R and 22RE engine, when the coolant goes through the heater core it gets cooled off enough that when it gets dumped back in on top of the t-stat, it shuts it. Therefore the temperature in the engine continues to go up. A 2-stage thermostat, Toyota p/n 90916-03070 should solve the problem.

[1990COTOY]

Do I have to special order that from Toyota, and how much does that cost?