Towing Question - OD or 3rd Gear?

PharmZ71 · May 18, 2003

I am towing a 18 foot boat with my 97 K1500 (5.7L), 3.73 Gears. Today I was pulling it home in a headwind on the interstate..doing about 70 mph, and the tranny would shift from like 2000 to 2500 rpms when going uphill. Thinking it was shifting to 3rd, I just manually put the tranny in 3rd to try to keep it cool, and the rpms jumped to around 3000 rpms?? I was confused. It acts like it has 5 gears.

So is it better to throw it in 3rd and let the motor run at 3000 rpms, or should i just let it do it's overdrive thing? I know shifting up and down is hard on the tranny, but 3000 rpms for a long time seems like a lot of work for that enginge. I don't know what would be better for the truck.

Any thoughts?

SilveradoWV · May 18, 2003

Usually if its shifting alot I just leave it in 3rd. Leaving it in third doesnt really hurt anything except the MPG IMO.

Shaners · May 19, 2003

You were in OD... Sometimes the torque converter was locked and then it would unlock...

The locking and unlocking of the torque converter creates alot of heat, and in this case you are better off pulling the gear selector into "3" and turning the higher RPM's.

Sometimes when towing, turning more RPM's is a good thing, because it keeps the motor in the powerband, and could actually increase your MPG's.

An easy test to see how well your towing power is... No cruise control and hold your foot steady on the gas on a flat section of road while in OD. Don't move your right foot and pull the gear selector into "3" and if the truck starts to pick up speed even though the RPM's are higher, you'll be able to let off the gas a little and will save some fuel...

The higher RPM's put the motor up where the power is...

canadianchevy33 · May 19, 2003

I think the only downside to running in 3rd would be the decreased fuel efficiency but its easier on the tranny most definetely so its not shifting up and down.

k1500chevy97 · May 19, 2003

usually 3k rpm is right around the sweet spot as far as power goes

As said before fuel mileage might suffer a bit

Drop it down into 3 before and on grades and in headwinds on flat ground I would use OD

timk49 · May 19, 2003

I used to tow my 6000 lb trailer with a 95 Silverado 1500 4x4.

It had the 5.7 motor. I used the OD on the level highway and shifted to 3rd on hills. I started doing this after boiling the tranny fluid on a long upgrade. I don't think the transmission in that truck was near the piece of machinery that goes inth the HD trucks now. And I really am sold on the tow / haul mode. Service the trans often and enjoy the boat.

THE BIGPUNN · May 19, 2003

i agree on the other posts. i tow a 5500lb travel trailer and i drive the 3rd unless im on the highway on level ground and the tranny is shifting itself ok.

mdscole · May 19, 2003

The trick is to keep the torque converter locked. If you can do that in OD because the load is small, then go for it. As soon as the transmission unlocks the torque converter, shift down. When you press down on the accelerator while cruising at speed, first the transmission unlocks the converter (about 400 rpm increase). If you press further, the tranmission drops into 3rd. The converter locks in 3rd and OD.

You have a 4L60E transmission in that Z-71. Most of them came with transmission coolers. You might want to check (It's mounted in front of the condenser). If you don't, it's a worthwhile investment.

80% of transmission heat comes from an unlocked torque converter. The hydraulic connection between the transmission and the engine is loose, and the friction in the unit generates alot of heat. By locking the torque converter, the input and output sides of the converter are spinning at the same speed through a mechanical transfer instead of hydraulic. Mechanical does not genrate heat. This is why you want to pick the right gear.

Of course if you have a manual tranny, it doesn't matter.