What's seen as the optimal highway speed..?

[DarbyWalters]

In my Jeep Diesel the second Overdrive Locks up at 64mph and I can keep it locked down to about 59 or so...less than 1700 prms with a 4 banger...yields about 30mpg for a 4300# SUV.

[spacepilot]

Several posters mentioned the torque converter lock-up. How do you get that information? From the engine speed, or does the scan gauge provide that information?

[DarbyWalters]

You can feel it and see it on your tach. If it is not locked it is slipping (thats what auto do). If you hold steady speed and it locks up...the rpms drop a few hundred...it almost feels like an extra gear sometimes.

[trollbait]

Side note do any of you Prius owners find that car tends to wander a bit - I seem to have a hard time keeping it going straight and the steering seems very stiff with 18k on the odo.

I've notice it. It is likely the OEM tires. Few people are happy with them. Plus, the toe in spec is 0 degrees.

[basjoos]

My mileage is the same between 30mph and 65mph. My Cd is low enough that the slight increase in aero drag through this speed range is countered by the increase in engine efficiency as the load increases on the engine.

[guest001]

I'm not really in this thread, but just to add from my experience, I get the best at 55 or less then 60. I can see the gas go, above that.

really any time I let the load go lower then 15, I don't get that great of mileage.

[spacepilot]

Originally Posted by DarbyWalters

You can feel it and see it on your tach. If it is not locked it is slipping (thats what auto do). If you hold steady speed and it locks up...the rpms drop a few hundred...it almost feels like an extra gear sometimes.

I see. I use the cruise control to accelerate extensively, and it seems to do a good job at shifting early and keeping the engine load in check. I don't notice the tack needle shoots up too much during acceleration, so maybe the cruise control locks the torque converter too, and that's why I don't notice. On the other hand, when I coast on certain declines, I do notice the torque converter going in and out of lock-up. Thanks for the explanation, DarbyWalter.