mmarshall

Yes...this is true in high-mileage transmissions that have had little or no maintenence. The seals are usually in poor shape, and the dirt inside the transmission and in the fluid is basically what is keeping the seals plugged and keeping the fluid from leaking out. Flush a transmission in this condition and all you will do is force out the dirt and the decayed seal pieces with it. Then..... when you put in new fluid, the first time you shift it into gear, the fluid will run out all over the place because the transmission will be full of holes and slits inside and out..

GRAND_LS 4

iTrader: (2)

I must respectfully disagree. Normal driving condition would probably consist of light country driving. Because I know for a fact that my tranny gets its fair share of abuse in my daily stop and go traffic during rush hour.

My car was driven by only ONE owner before me, an older gentlemen in his 60's, and when I drained and refilled a few times when I first acquired the car, my tranny felt much smoother when shifting (he preformed full dealer service per manual and then some). My car doesn’t have many miles either comparing to the other LS owners, so I’m not sure what you mean by the vehicle life. Is that 100K? 200K? 300K?

I think a drain and refill is a must every 30K, I do it more often, but I’m in a lot of stop and go traffic daily. Unfortunately many of us are not able to exercise normal driving condition during our daily commute (but I wish I did).

Lexusfreak

Well said GRAND! Couldn't agree more.

SCV8

The Toyota spec ATF appears to break down, using some sacrificial element, or chemical as a friction modifyer. Other automatics don't seem to do this, and I've never had a tranny behave like the one in my SC, I suppose it could help the trans to last longer if the fluid is regularily maintained.

HarrierAWD

Respectfully disagree, too. Don't let my Colorado location fool you. I'm a transplant. I drove in stop-n-go NYC traffic for 19 years. None of my cars ever had black or discolored tranny fluid. "Normal" driving condition means what most drivers encounter - rush hour traffic. Severe condition means when towing a heavy trailer without a tranny cooler, or often doing "bank jobs" and participate in high speed police chase.

Believe it or not, tranny fluid isn't working the hardest in stop-n-go traffic. It's the long high-speed highway trips that could overheat the tranny, provided that the cooling system isn't working properly. Tranny fluid can deteriorate when it experiences temperature beyond its design limit.

Black fluid means something's wrong with the tranny or cooling system *and* the owner does not check the fluid regularly. The tranny fluid need not be changed under normal condition. If you have any doubt, check the owner's manual or the tranny dipstick.

And yes, it feels great driving on Colorado country roads.....