Posted by Ben on January 20, 03 at 10:54:27:
In Reply to: Re: Compare it to climbing stairs posted by Bruce on January 20, 03 at 10:20:39:
Distribution of forces is one. Meaning it's distributed over more gear teeth over same period of time.
Leverage. Longer lever with lower gears means less effort for given amount of work.
Fluid shear in TC. Some TC's lock up in Drive or 3rd gear too. Working it harder will have the tranny computer drop out of lockup, like towing in OD. That will then put the fluid in shear, causing more heat (loss in efficiency). Married with the lower fluid flow is what you've discovered, less fluid flow to the coolers (in tank and external) will have less heat rejected. Even if the flow is high enough, the fact is that the fluid will shear and create tremendous amounts of heat that would NOT have been there if the TC was locked. That will age the fluid, even burn the fluid.
Placement if the gauge is critical, but you can't put it where it's shearing (the hottest spot) because that takes place inside the TC. There is an additive affect and in time will show in the output of the fluid to the coolers...but by this time, the fluid is shot. This is part of why racers who choose high stall TC's must have external coolers and use higher shear fluid (synthetic). Better than no gauge, but still an after affect...so drop down a gear or slow down.
Then take a look at the whole system. There's BTUs being generated by the engine too. It's working harder in OD than in 3rd. That means it's also pumping more BTUs into the radiator, which has the intank tranny cooler...note that the intank tranny cooler is on the cold side tank and any BTUs that is dumped in there by the tranny is NOT cooled by air flow and is pumped STRAIGHT into the engine as "coolant", thereby raising the ambient fluid for the engine, which is already in high BTU output mode.
Throw in higher parasitic drains on the engine during this scenario. Like the AC is on (parasitic drain on the serpentine belt, loading up the engine) and heating the ambient air flow through the radiator. Alternator supplying the AC system. Fan clutch engages and can draw 15-25hp from the serpentine belt. ETC, ETC...
Gears and lub. With the lower gears and the better leverage, there is another thing that affects. The amount of time the gear faces touch each other...actually...gear faces do NOT touch as designed. The fluid spec (viscosity, film strength, etc) is designed to have flim of lub on each side and the gear faces rides on that film. Metal to metal is NOT supposed to happen, but for infrequent during shock loads. Going slower has high chance of going metal to metal. Getting the fluid too hot ditto higher chance of metal to metal. Getting fluid burnt ditto.
None of these are instant death, but micro deaths over time.