Originally Posted by Red-Stripe
I'm glad I saw you post this same explanation as you did last year when you explained why the TQ isn't allowed to lock up for some miles in winter. it's been bugging me to ask and clarify you saying "it's more efficient". Maybe you mean to say "it shifts better"?
What doesn't make sense to me, is that 100% of transmission losses convert to heat energy, and nothing else (unless there is noise energy), so a cold "inefficient" tranny will self heat from slippage. Why use precious needed heat( for engine efficiency) from a cold engine, or slip a TQ? Seems like you are just stealing needed energy from one area to feed another. I know my mileage suffers in the winter when the TQ doesn't lock, which makes the engine run faster turning the un-needed mechanical fan faster etc...
The main temperature-related factor is the transmission fluid viscosity. The trans fluid is thinner at higher temps. So the trans efficiency is higher (at higher temps) because the fluid is easier to pump and move (like squeezing it out of the gear teeth as they mesh).
With government standards mandating higher and higher fuel economy (why is it any of the government's business how much fuel economy my vehicle gets?!?), manufacturers are being forced to do lots of "unnatural" things to meet the standards. Like making your transmission run at 180°F instead of 130°F. This will actually reduce the life of your transmission (cooler is better for longevity), but your friends in the government care more about fighting "global warming" than they do about how long your vehicle lasts (or how much it costs, or how well it performs).