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straightw8 View Drop Down
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  Quote straightw8 Quote  Post ReplyReply Direct Link To This Post Topic: Malfunction Indicator Lamp
    Posted: 01-Jul-2008 at 22:48
If the t-stat fails, dosent it usually fail in the open position, thus meaning that no real harm is going to ocurr to the car.. it will always just get a full flow of coolant?
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  Quote ___/ __/ _/ Quote  Post ReplyReply Direct Link To This Post Posted: 03-Jul-2008 at 00:24
Originally posted by straightw8

If the t-stat fails, dosent it usually fail in the open position, thus meaning that no real harm is going to ocurr to the car.. it will always just get a full flow of coolant?



I would imagine that if the t-stat is always open, then the engine will not get up to temperature (at least short trips) and have a negative effect on fuel mileage or __________ ? Anyone have any further comments?



Mike
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-dstathos-

^Pure Genius! Why didn't I write that?!?

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rustybronco View Drop Down
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  Quote rustybronco Quote  Post ReplyReply Direct Link To This Post Posted: 03-Jul-2008 at 05:56
Originally posted by ___/ __/ _/

Originally posted by straightw8

If the t-stat fails, dosent it usually fail in the open position, thus meaning that no real harm is going to ocurr to the car.. it will always just get a full flow of coolant?



I would imagine that if the t-stat is always open, then the engine will not get up to temperature (at least short trips) and have a negative effect on fuel mileage or __________ ? Anyone have any further comments?


I think I agree... assuming it does fail in the open position, I don't think there would be much harm in the short term - other than not running at optimum conditions, as Mike said above. In the long term I think it would be more wear tear on the engine if it is always running cool - following the vane of thought that I always hear that it's not good to rev the engine high before reaching normal temperature operation.

The two thermostats I've had fail in cars over the years; one started acting erratically w/ large temperature swings. With the other one the car would try and overheat whenever stopped - the thermostat would not fully open. Though the cooling system is much more advanced on the W8. From what I understand the thermostat is controlled with an electric heater and maintains a 90C temperature - if the heater or control circuit fail, the wax in the thermostat will open it at 110C.

I'm not convinced the thermostat always fails in the open position though. I've always tested them by heating them in a pot of water to see if they open up.

perhaps helpful from a previous thread:
Originally posted by VWAffe

Also look here on the Vortex... the W12 has the same system, and some have failed. By comparison, ours is easy to get to!

I've been busy reading a copy of SSP 222... it's really a neat system, and judging by the price of a thermostat, I think VW is proud of it!


Edited by rustybronco - 03-Jul-2008 at 12:10
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Posted: 04-Jul-2008 at 00:23
Failing full open would be the best way to have one fail - sure the car wouldn't warm up well, but it wouldn't hurt much other than the emissions and economy.

I've seen them fail mostly by not fully opening.

The achilles heel of the W8 thermostat seems to be the heating element... it'd be an incredibly bad day if someone tried to keep driving one whose wax piston failed.
'03 W8 Sedan 6MT     ..."it goes to 11!"
'02 V6 Wagon 4Mo 5MT (Swap In Work)     ...both black on black w/ limo tint
'14 JSW TDI 6MT
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  Quote rustybronco Quote  Post ReplyReply Direct Link To This Post Posted: 04-Jul-2008 at 08:01
I was looking in the Bentley manual yesterday - I didn't actually see a procedure to replace the thermostat, just expanded drawings showing where it is. But it looks like you just have to remove the intake manifold and it is right there.

I suppose the real question is how hard is it to replace the heating element or control unit.

Edited by rustybronco - 04-Jul-2008 at 14:03
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  Quote VWAffe Quote  Post ReplyReply Direct Link To This Post Posted: 04-Jul-2008 at 11:26
The heating element is part of the thermostat... inside the wax piston. Unfortunately VW only sells the thermostat as a unit, for something like $385 if my memory is correct.
'03 W8 Sedan 6MT     ..."it goes to 11!"
'02 V6 Wagon 4Mo 5MT (Swap In Work)     ...both black on black w/ limo tint
'14 JSW TDI 6MT
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