Coolant flushing - best practice

[alchemist]

On cars with the Automatic temp control, what is the best way to flush? I'm guessing you'd need to pull off the temp control valve so it would let coolant go into the heater core? is there a write-up on this?

thx.

[91grandmarquis]

My car has the auto temp control, when I did the flush on the coolant I just opened the radiator and stuck the garden hose in the filler neck, I then ran the car up to temperature so the thermostat would open. Just watch the color of the excess fluid coming out of the radiator, it should turn clear after about 5-10 minutes. I ignored the heater core being open to coolant under the assumption that anything in there would be minimal considering the total volume of coolant in the motor. Then I just filled the car back up. Make sure your overflow container is empty so that the coolant in it does not get sucked backwards while you run the hose, this will make it take much longer for the liquid coming out the filler neck to look clear. Anyway I kinda did it the redneck way and it does make a mess, but I didn't bother to mess with the heater core and still got a lot of rusty colored gunk out of the block and radiator.

[85crownHPP]

Flushing the heater core in an older car can clean out enough gunk to open up leaks as well... If you are getting good heat inside the car, I wouldn't worry about it. At the most Id take loose a heater hose and run a light stream through it.

PS, our cars have no heater control valve that restricts flow to the core. Our doo-dad inline in the hose is just a sensor for the thermal blower lockout.

[86VickyLX]

Yeah that thing just doesn't let you have floor heat until the coolant has warmed up so much...

[gadget73]

I've always kind of wondered if fitting a pair of vacuum-actuated heater control valves might be useful. Plumb them to manifold vacuum so it shuts the heater core off when you stab the throttle and drop the manifold vacuum. It might help keep the core from blowing up on cars that get driven hard frequently.