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Thermostat heater resistance

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tripwalking View Drop Down
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  Quote tripwalking Quote  Post ReplyReply Direct Link To This Post Topic: Thermostat heater resistance
    Posted: 26-Apr-2010 at 12:52
I'll explain what I'm thinking first, then see if anyone has any thoughts.

This whole thermostat heater thing is on my mind... I've got a thermostat code and the cooling fans are turning heads in parking lots everywhere. The heater element seems a bit overkill to me - I have been involved in many "higher-than-measly 275hp-W8" engines and none of them have a thermostat heater. I don't drive the car like a mad man - I rarely floor it. Here's my hunch: snip the wires going into the thermostat, and install a resistor with the same resistance as the heater element. Now the computer thinks there's a perfectly good heater again, and the regular old thermostat can keep doing its thing.

Is anyone with a functioning thermostat heater able to measure the heater resistance with VAG-COM?
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yesimalex View Drop Down
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  Quote yesimalex Quote  Post ReplyReply Direct Link To This Post Posted: 26-Apr-2010 at 18:38
I've often wondered the same thing. If possible could it also not be installed "inline" and avoid removing the manifold cover and fuel rails.
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  Quote tripwalking Quote  Post ReplyReply Direct Link To This Post Posted: 26-Apr-2010 at 18:49
That's what I was thinking too... just find where the wires go into the back of the intake.

My sig should be "you just got burnt by a wagon with three car seats in the back"
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Posted: 26-Apr-2010 at 23:46
Originally posted by tripwalking

... Here's my hunch: snip the wires going into the thermostat, and install a resistor with the same resistance as the heater element. Now the computer thinks there's a perfectly good heater again, and the regular old thermostat can keep doing its thing.

...


Sorry to rain on your parade, cause it's good idea, like dioding the rear O2 sensors on various cars for a "temporary" fix.

However, the ECU can tell if the thermostat is operating correctly by the change in the coolant temperature. On a healthy car, for example, if the ECU calls for an increase in cooling, it increases the pulse width (percentage of time it's "on") of the voltage to the thermostat heating element, which causes the thermostat to open a little more. The ECU then watches for the engine coolant temps to drop correspondingly, and controls the temperature by modulating the pulse width.

Your fans are going nuts because the thermostat isn't responding to the ECU as it expects, so the ECU is going into failsafe mode and using the fans to make up the difference.
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  Quote tripwalking Quote  Post ReplyReply Direct Link To This Post Posted: 27-Apr-2010 at 00:39
Is the thermostat different than the standard spring type? I don't mean the electronic aspect of it - the part of it that controls the actual fluid passing through. Because if it's still a spring type thermostat, I'm wondering if I can just bypass the heater and let the good old thermostat do its thing.

It won't hurt anything to try it out - maybe a few fuses.

I wonder how often the heater actually kicks in? This could be why, when after the code is cleared, the light doesn't come on right away... it's not tripped until the heater actually is "required" (?)
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  Quote yesimalex Quote  Post ReplyReply Direct Link To This Post Posted: 27-Apr-2010 at 08:06
Well so much for that quick fix. I find the fans to be mysterious at best. Mine were running full force for 3 days and then just quit. I was doing about an hour trip down the interstate and stopped for gas no lear jet when I turned the car off. Haven't been on again since. My Vw mechanic is sure it's the temp control unit, though he didn't actually look at it too hard obviously. At this point I'm more concerned about wear on the fans than anything, one already has developed a shrill shreaking noise.
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  Quote rustybronco Quote  Post ReplyReply Direct Link To This Post Posted: 27-Apr-2010 at 15:07
Ya, the smaller of the two fans is W8 specific and pretty expensive - i just had to replace it. I don't know dealer price; I bought if from my local mechanic and installed it myself. He charged $300, I don't know his mark up but I'd be surprised if you can find it less than $150.
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  Quote yesimalex Quote  Post ReplyReply Direct Link To This Post Posted: 28-Apr-2010 at 19:45
wunderbar

Don't suppose you could do a write up on that install could ya??

Edited by yesimalex - 28-Apr-2010 at 19:48
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Posted: 28-Apr-2010 at 21:38
Alex - odds are your thermostat is failing intermittently. Mine has done the same... not worked, then out of the blue been fine for a while.

Trip - yes, the thermostat has what I like to call a "failsafe" range where it works just like the regular variety. However, it doesn't kick in until around 100C to avoid catastrophe when the ECU-controlled range fails. Under normal operation, the ECU is constantly controlling the thermostat to maintain specific temperatures around 90C. I have a good SSP that explains it all, but it's in German. Look for the post I started on my T-Stat to read more...

Cheers!

Edited by VWAffe - 28-Apr-2010 at 22:08
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'02 V6 Wagon 4Mo 5MT (Swap In Work)     ...both black on black w/ limo tint
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  Quote tripwalking Quote  Post ReplyReply Direct Link To This Post Posted: 28-Apr-2010 at 23:24
Why does it need to run so cool?

I'm not being sarcastic btw :) You could run a small block chev at 220f (~104c) all day.

p.s. got any extra W8 thermostats hanging around? ;)
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