Overdrive on or off?

[fred01]

I own a 2001 Pathy with the 3.5 and I tow a boat and trailer that weighs around 2500 lbs. I added an external transmission cooler and also air bags on the rear coils. I usually only tow less than 100 miles locally but I am planning on a trip, of about 800 miles one way, later this year.

 

My question is, what do any of you do on a long haul...leave the overdrive on, or turn it off?

 

I get both answers; leave it on and the tranny will run cooler, leave it off so you don't lug the motor and keep the transmission from shifting back and forth. I usually drive about 60 miles an hour so OD on is just around 2k RPM's, OD off is around 3k RPM's.

I didn't find anything in the owners manual about the OD except for uphill and downhill.

Edited September 3, 2008 by fred01

[91PathSE]

OD OFF, with it on you ruin 4th gear..and it will be shift evrytiem you even tap the gas to stay at the same speed..so leave OD off and eth tran will stay in 3rd and youll have alot less shift 3rd-4th it will only be when you really press down and it goes to 2nd or 1st

[XPLORx4]

My strategy for OD ON or OFF is to pay attention to the shifting patterns of the tranny and decide when I want to use 3rd or 4th gear myself. If the tranny shifts a lot between 3rd or 4th, or even if the torque converter slips frequently in 4th, then turn off OD to lock the torque converter in 3rd gear.

 

The main reason for turning off OD is to prevent the TC from slipping, which generates a lot of heat. You can tell when the TC is locked or unlocked in 3rd or 4th gear because the RPM will increase slightly (approx 300-400rpm) when you give it a little more gas. If you increase the throttle even more, the tranny will downshift (RPM difference approx 1000) to try to honor your request for faster acceleration. Then, if you let off the gas to a steady cruising speed, the tranny will upshift back to 4th gear, then lock the torque converter (which feels like another small "upshift").

 

The tranny behaves like this:

 

Acceleration to 60mph in D; OD on:

1st gear (TC unlocked)

2nd gear (TC unlocked)

3rd gear (TC unlocked)

4th gear (TC unlocked)

4th gear (TC locked)

 

Under load or mild acceleration (@ 60mph in D; OD on)

4th gear (TC unlocked)

 

Under heavier load or moderate acceleration:

3rd gear (TC unlocked)

 

-------------------------------------------------------

Acceleration to 60mph in D; OD off:

1st gear (TC unlocked)

2nd gear (TC unlocked)

3rd gear (TC unlocked)

3rd gear (TC locked)

 

Under load or mild acceleration (@ 60mph in D; OD off)

3rd gear (TC locked)

 

Under heavier load or moderate acceleration:

3rd gear (TC locked)

 

-------------------------------------------------------

Acceleration to 55mph in 2; OD off:

1st gear (TC unlocked)

2nd gear (TC unlocked) *below 50mph

2nd gear (TC locked) *above 50mph

 

In 2nd gear, the TC will not lock below 50mph.

[02silverpathy]

One last thought with the 3.5, the variable timing adjusts its curve around 2250-2500 RPM and the engine is definately most effcient in the same range. I can safely report the efficiency because of the information that my Scanguage II gives me. The MPGs are at best in town with OD OFF up to/under 45mph, with OD on the tranny switches alot and wastes gas trying to stay in an "efficient" gear.

 

In the cold Winter months when you are first pulling away from your parking place just barely feed the gas pedal and watch the tach while listening to the engine...right around 2250-2300 the engine perks up and the exhaust note sounds smoother---I would tell you that the Scanguage II tells me the exact degree of timing but timing changes faster that the Scanguage can report even on its quickest refresh rate!

 

I too have reduced my HWY driving to about 65, as with lift and tires this is my best shot at getting to that 20 MPG...this leaves me (tires/gears offset) at 2500 RPMs!

[BowTied]

Medium to heavy loads = OD off. The extra fuel is way cheaper than a trans rebuild. JMO

[fred01]

Good info! I didn't realize the torque converter locks up in third as well as fourth. I've noticed the lock up in fourth gear but I haven't paid attention to third too much. Thanks.