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Thermostat or battery

This is doing my head in. For some time (a year) my VW Passat diesel (2000) has been just slightly sluggish at turning over from cold. It's never fail ed but with winter approaching I don't want it to. I'd had the battery test ed last year and it was found to be OK but decided to give the car to my lo cal VW dealer to sort out. At the same time, I asked them to replace the th ermostat, because it seemed to me that it was taking too long to get up to temperature compared to how it was when I first acquired it (as a demonstra tor with 9K on the clock). When I asked the dealer how they had got on they said that the battery was not too good and replacing it would cure the the rmostat problem as well as the starting. Eh? I thought. I was given an expl anation by the service manager as to why this should be so re the thermosta t but it seemed complete rubbish to me. But maybe I'm not up-to-date with h ow thermostats work these days. Could one of you kind guys please illuminat e me as to why the service manager was NOT talking rubbish - if this is, in fact, the case.

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cryptogram
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ervice manager was NOT talking rubbish - if this is, in fact, the case.

Perhaps your car has the built in water heater that runs off the battery and takes a huge load, it probably only comes in if the battery is up to scratch.

Reply to
Mrcheerful

000) has been just slightly sluggish at turning over from cold. It's never failed but with winter approaching I don't want it to. I'd had the battery tested last year and it was found to be OK but decided to give the car to m y local VW dealer to sort out. At the same time, I asked them to replace th e thermostat, because it seemed to me that it was taking too long to get up to temperature compared to how it was when I first acquired it (as a demon strator with 9K on the clock). When I asked the dealer how they had got on they said that the battery was not too good and replacing it would cure the thermostat problem as well as the starting. Eh? I thought. I was given an explanation by the service manager as to why this should be so re the therm ostat but it seemed complete rubbish to me. But maybe I'm not up-to-date wi th how thermostats work these days. Could one of you kind guys please illum inate me as to why the s

Ah! I never knew they had these. That would tally with the explanation I wa s given although maybe he could have expanded on it a bit! I've never heard of a water heater in this context.

Reply to
cryptogram

s

They live in a lump on the engine that looks like a thermostat housing, three or four diesel heater plugs screwed into a casting that the water runs through, I believe they were probably a bodge to get the engine through better emissions regulations, but they have the useful side effect of getting the windows demisted quicker. The downside is that they draw very heavy current, with modern electronics the system sees them as an unnecessary load on a compromised system (weak battery) and turns them firmly off. (I am sure that someone with better VAG knowledge will be along shortly to confirm or repudiate this :)

Reply to
Mrcheerful

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