digging up the dead here, but maybe it will help somebody in the future...
Quote:
Originally Posted by ShadeTreeMech
I'd alter my transmission to think it was always warm enough to lock up, but for fear of damaging something. Simply finding the correct amount of resistance to simulate a 180* transmission would be simple, but does locking up the TC when it is cold do any harm? I suspect it is an attempt to get the engine warmer faster in part, but it is hard to know without knowing automatics as intricately as I'd like to.
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the TCC will likely lock up slightly harder/faster than normal(but not at the levels required to damage anything). and yes, TCC lockup is specifically delayed to allow the coolant and trans temp to raise to a higher value before lockup. if i take off with my coolant temp at ~80*F, i'm usually up to 55MPH before coolant hits 100*F, then while traveling at 55 with the TCC unlocked, coolant and trans temps rise pretty quickly, when coolant hits the 140*F mark that i have set for minimum TCC lockup, the rate of coolant and trans temp rise drops significantly. where it takes ~1 mile to get the coolant from 140*F to ~170*F with the TCC unlocked, with lockup enabled, i'll only be at ~155*F or so in the same distance. so instead of ~2 miles to get from 140* to 195*, it takes 4 or 5...
not that it's a problem, since i'm in closed loop by 100*F, but it MIGHT cause more wear to the engine parts that like to be a bit warmer before they're worked harder(pistons come to mind).
also, another "reason" for lower winter MPGs.... the higher air density caused by colder air that causes more aerodynamic drag? well, it's a double-whammy and also causes more pumping losses since you will need less throttle to maintain a specific power output due to the colder/denser air.
it's tough to monitor if you're not looking for it... the increased aero drag requires more throttle while the increased air density requires less throttle... have to look for small changes in MAP or MAF readings.