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Old 12-04-2012, 08:15 AM
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doru doru is offline
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Location: Calgary
Join Date: Sep 2007
Posts: 4,703
Mein Auto: 2003 530iA
I believe I know what's causing my high fuel consumption.

I think I have a lazy thermostat. It's not stuck open, I have no codes with GT1. But, I know, this car should heat up pretty quick, which it does not.
Now, with cooler ambient temps, I noticed it took forever for the needle to go to the 12 o'clock mark. I also noticed that the instant mpg goes down drastically until the needle starts to stabilize, then the instant mpg is what it should be.

For the last few days, i did the KTMP test after cold starting (ambient temps around -12C to -14C). So, here is what I noticed: the temp climbs nice and steady antil reaches the 55C to 60C mark. At this point, it takes forever to get to 94C. In distance: it takes about 300 to 400m (yards) to get to 55C, then another 4 Km or 5 Km to reach 92C to 94C. The needle stabilizes at 12 o'clock around 72C.

I think that while the GT1 does not show a failed thermostat, the bloody thing opens way to early at the 55C to 60C mark, instead of the 94C mark.

My commute is about 12 Km one way, so with colder ambient temps, it's no wonder that now my mpg is even worse. As I said, the GT1 didn't find a single issue with my car, which is strange the way the t-stat is acting up. I remeber having the needle at 12 o'clock very soon after starting the car stone cold, which is not the case now.

Anyone else experienced this? My t-stat is a dealer OEM changed October 2010.
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