While searching for information on exhaust heat recovery, I found a paper yesterday (and can't find it now, grrr) that said that an automatic transmission saw a 2.2% FE increase from preheating the transmission on a 30 minute drive cycle test. Not bad for a 30 minute drive! The shorter the drive, the greater the effect the cold start has.
Edit: Yay, I found it:
https://etd.ohiolink.edu/!etd.send_f...osition=inline
Quote:
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Using a novel oil routing method, the transmission fluid reached its operating temperature in 40% less time than in the baseline set by a conventional transmission oil system: 15 minutes compared to 25 minutes. This resulted in a fuel economy improvement of 2.2% during a 30 minute drive cycle. As with the engine oil, although on a smaller scale, quickly warming the transmission oil has a decidedly positive effect on vehicle efficiency.
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