Kellog13 wrote:
Sounds sorta like the same thing. Then if this is correct, the OD off is in fact 3rd with 3rd TC lockup. That means with OD off you loose two gears?
That seems to be the general consensus, looking at everyone's input.
If I'm going to be just puttering around town, where the fastest speed limit is 45 mph, I'll lock out OD before I even pull out of the driveway.
From what I've seen doing some checks with an infrared non-contact thermometer, the FSM is correct - being in lockup does significantly reduce tranny fluid temp. A 25 mile run at 70 to 75 mph in lockup produced temps nearly 20 degrees lower than a 10 mile run around town at 45 mph without lockup.
Especially during the summer in city traffic, such as Fabian has to contend with in Charlotte (I live 25 miles north and I pity anyone that has to put up with that traffic every day), it could help keep tranny temps down to acceptable levels.
Another advantage I've found is that I get a slight amount of engine braking until it drops out of lockup. This helps contend with the ebb and flow of in-town traffic, reducing the amount of time I have to be on and off the brake.
Nearly half of my 20 mile commute is a 45 mph section of highway. From memory, at 45 mph, it's virtually a wash as far as engine rpm, locked and unlocked. With OD locked out at 50 mph it's turning 2100 rpm.
To be honest, I would rather have the higher 5th lockup speed at 62 mph. On some of the hills I have to contend with in the 55 mph section of my commute, if I hit 58 mph and it goes into 5th lockup, it feels as if it's lugging up hill at that rpm, and have to drop below 55 to get it to drop back into 4th lockup. Gets a little tiresome sometimes "threading the needle" on that 3 mph window on a winding hilly country road.