None taken. You WERE right in making sure the correct terminology is used. Things can be confusing enough without exchanging terms.

Some have reported shifting problems, shuddering, and other issues when using synthetic fluid. Considering this part of the transmission'* operation...

...dropping your rpms during lockup may be having your transmission work in ways other than designed.

I'm not seeing how a different oil can lower engine RPM'*. You would have to have a strain on the engine, or just drive slower to have lower RPM'*.

im sorry but you can put straight 50w oil in your engine and it wont effect your rpm'*
at a given (70 mph) speed. but i wholeheartily agree about synthetic oil getting
better gas mileage. i've ran nothing but M1 5/30 for 135,000 miles.

ROD

I've got to start reading things more closely. I thought he was speaking of synthetic tranny fluid. I agree. Whether you use synthetic, or dino oil, it won't have any affect on the engine rpms for a given speed.

Testy, testy, c'mon! LOL . Looks like everybody agrees that the torque converter lockup doesn't happen until the transmission oil temperature is up And it sounds like overdrive is another word for 4th gear, which it will grab even cold. What is torque converter lockup though, and how does that have the effect of another higher gear??

Here'* how I understand it:

Torque converter (TC) lockup is when the two halves of the TC are locked together to create a direct connection between the engine and transmission. During acceleration the TC is a fluid clutch between the engine and transmission, but when the car settles at cruising speed the PCM will electronically lock the torque converter. This means that instead of the impeller (input side) spinning at engine speed and transmitting torque through the transmission fluid to the turbine (output side), a clutch actually locks the components of the torque converter together at a 1:1 ratio (though as Archon pointed out, there is actually a calculated amount of slip during lockup). This greatly reduces heat in the TC and transmission fluid, because there is no longer the friction of the impeller spinning at a higher speed than the turbine. The 1:1 ratio also reduces the RPM that the engine must turn in order to move the tires at the desired rate of speed. Thus, when the torque converter clutch locks up, it may seem as if you're going into another gear because your RPMs drop by a few hundred. The net effect is a cooler transmission that will last longer, and better gas mileage because of reduced engine RPM at cruising speed.

Great explanation Ben, thanks! Lockup sounded like a mechanical connection of some type, but now I understand its a very efficient hydrodynamic transmission mode.

Always good to learn something is going to make the transmissions last longer and run cooler instead of being problematic Do our 00-05'* also have a transmission cooler?

Yep, inside the radiator.

I'm abit comfused, I don't see how that'* possible since it'* all about gearing.

Can someone correct me on that?

no, your right, when the TC is locked up than oil will make ZERO difference