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[Solved] Drain Coolant + Open Heater Control Valve ? (Old Car)


Topic starter

Hi Folks,

I've got a JDM Toyota Celsior 1997 35,000 miles VVTI. I was watching a video of a mechanic working on a 1997 Toyota T100 with a heater control valve going to the heater core. He recommended opening it when draining the coolant. Would I need to do this on my car as well? It makes sense I think. I should really get a repair manual.

The temp gauge is going up quickly from cold and I found a site that said this could be the cause. When the weather improves I will replace this valve (plastic /age), thermostat, temp sender, coolant temp sensor, maybe radiator as well. Head gasket is ok.

Thanks and all the best.

2 Answers

Yes, if there's a control valve on the heater core you'd want that open so the coolant in there is changed out as well. A repair manual would definitely be a good investment if available.

I wouldn't think the heater control valve would cause a problem with engine temperature but I'm not familiar with the cooling system on that car.

@Chuck Tobias Thanks very much for your reply. I just caught a sentence here: where they say "A faulty heater control valve may also cause the temperature gauge to behave erratically, rapidly climbing and falling" but they don't go into detail, so maybe just touting for buisness and exaggerating a bit.

@MountainManJoe I'm not very tech savvy and just noticed another post where you say not to enter html tags into posts. Did I do that here? Thanks.

First I've heard of a heater control valve causing that symptom, it probably depends on the specific vehicle design. I don't see any HTML tags in your post. The site automatically makes URLs clickable.

Cool, one less thing to worry about, thanks again.


I usually just unhook the heater hose and run water through it.

I also unplug the radiator hose and run water through that.

Then I don't have to worry about any heater valves or thermostats.