Why does the stock heater valve not close fully?

[bloc]

I've seen elsewhere on this board that the OEM heater valve doesn't close fully, whereas the Dorman aftermarket one does.

Why did toyota design it this way? surely it isn't an oversight. Did they want to keep water flow through the heater core at all times for some reason?

 

[LINUS]

Just as theoretical - I as an engineer want some flow at all times, promotes corrosion prevention by sediment laydown, also keeps pressure differential issues at bay, and as a side benefit lets some active cooling happen since you either have 1 or 2 extra heat exchangers in the system to shed heat.

It's like how the thermostat has that oriface to at least let some flow, just keeps the whole system at a common pressure - small details, overall big results.

 

[bloc]

I always thought the orifice on the t-stat was to avoid air bubbles getting trapped on the uphill side of the lower rad hose.. And the direction that the little check valve is installed support this.

But yes, those reasons are exactly what I guessed toyota was going for by maintaining a little flow.

Thing is.. it is very hot here. Personally I could accept those consequences for the benefit of keeping the heater core cool.

Anyone else with a solid reason I shouldn't stop all flow?

 

[ToothDr]

Are you getting hot/ warm air with the blower set to cold and the a/c off? I don't in my 1993. If not then what's the point. Toyota has solid reasons for design specs.

 

[aae42]

i don't think you have anything to worry about, mine is stuck wide open right now because it appears the servo that controls it is busted, and with the heat on full blast i still get 0 warmth... the blend door seems pretty tight... A/C working great at the moment with the mix valve full open

have to put on the rear heat to get heat in the cabin at the moment... not looking forward to taking apart the dash to get to that servo

 

[Cruiser Ed]

I'm going to say that the "OEM heater valve doesn't close all the way" belief is a myth.

Just for curiostiy, when I got my new OEM heater valve last year, I hooked up a hose on one of the closed valve. I filled it up hose with water at the sink and nothing came out of the other end.

 

[bloc]

i don't think you have anything to worry about, mine is stuck wide open right now because it appears the servo that controls it is busted, and with the heat on full blast i still get 0 warmth... the blend door seems pretty tight... A/C working great at the moment with the mix valve full open

have to put on the rear heat to get heat in the cabin at the moment... not looking forward to taking apart the dash to get to that servo

Strange. If it is the mix door both of mine do the same thing.. guessing should look at that.

I'm going to say that the "OEM heater valve doesn't close all the way" belief is a myth.

Just for curiostiy, when I got my new OEM heater valve last year, I hooked up a hose on one of the closed valve. I filled it up hose with water at the sink and nothing came out of the other end.

Interesting... I just went on what others were saying. Will probably do some temp measurements on the line itself.

 

[Tools R Us]

The OE ones that we have played with some close, others don't, the new/replacement ones appear to be the fully closing design.

 

[ranma21]

The OE ones that we have played with some close, others don't, the new/replacement ones appear to be the fully closing design.

The new OEM stock I have are fully closed. Not sure about the older version though.