Recently, my '89 mkIII (7M-GTE engine) has been having a coolant leak through the heater control valve. It's a little actuator and solenoid, on a bracket, behind the passenger-side strut tower, mounted on the firewall. There's a coolant line going into and out of the valve. Obviously, I've been having coolant level issues.

Appearantly, the heater control valve stops the flow of coolant to the heater core whenever the a/c is on full blast. Because this isn't really necessary and because it's $188 to replace this part from the Toyota dealer, people have been bypassing the valve. Bypassing involves just connecting the two coolant hoses.

Has anyone done this before, or heard about doing this. My main concern is that there are two small vacuum lines involved. I don't want to cause a vacuum leak; maybe I could just plug them up with silicon.

I wanted to ask the same question about this. I wanna hook the coolant hose straight to the heater control valve. Is this okay to do or is it hazardous?