Draining Transmission

While pondering a drain and fill of my transmission fluid (automatic) I had an idea and am wondering if it would lead to catastrophe. When I drain the fluid normally I get out about 3 quarts because that is all there is in the pan. What if, I drained the 3 quarts, then started the car to get a little more into the pan, thus getting more of the old out? Is being 3 quarts short going to do damage in 30 seconds? I just want to get more of the old fluid out.

bad idea, just go get some more fluid and pour it in there to flush the old stuff out.

Just drain the 3 qts once a year and you won’t have any sticking valves.

You’re already doing it the correct way. Don’t change anything.

Wouldn’t the new fluid mixing with the old fluid still in the t/m &/or torque do more harm? The new fluid would now be contaminated due to the old fluid.

You have the right idea, but the trans pump will run dry since the pan has no oil.

you could try the following method which is recommended by some manufacturers.

drain the pan
refill the pan
open the trans oil pressure line going to the radiator and direct the line into a waste container.

Run the engine, adding oil to the trans as the old oil is pumped into the container.

You must be careful about this method that you pull the correct line at the radiator and you contain the oil shooting out.  it can get messy.

Starting the engine with the pan empty is not going to do any good. The pump will be drawing air so no fluid will be moved through the transmission. The fluid in the torque converter will stay there as it is flung away from the hub. Without oil pressure the pump, input bushings, clutches in the input train, etc. are running without lubrication – not good. The best way to get more old fluid removed is let the transmission set for as long as you can; drain the fluid; fill to the correct cold level; run the engine while shifting the transmission through the gears; bring the fluid level back up to the correct cold level; drive the vehicle for 10+ miles and recheck that the level is at the correct hot level.


Wouldn’t the new fluid mixing with the old fluid still in the t/m &/or torque do more harm? The new fluid would now be contaminated due to the old fluid.

Even if you totally drained the fluid, disassembled the thing, cleaned off every pat and re-assembled it five minutes after you drove off the new fluid would no longer be new.

Just do as recommended. It works. If you follow that advice you will never need worry about damage or failure due to fluid failure.

Don’t do it. If the engine fan comes on, you might have a big mess. Don’t TRY to wreck things too often. Watch out for extreme decisions, they all sound good at first, but never accomplish the final goal: a perfect car. Not thinking crazy thoughts will give you more happiness.

The exchange method that uses the cooler lines works fine for some cars.

In everything, there is a level that becomes fanatical. If you exchange the fluid before it becomes significantly compromised, there will be no problem with the partial nature of the conventional change.