Towing in O/D

Both previous posters are correct when they talk about hunting between gears and tranny overheating, but one point in your original message caught my attention: Please define 'winding out' as you see it when towing in Drive. Naturally, you won't get a nice low 2000 or so RPM's when towing in drive like you do when not towing in OD, but an engine RPM of 3300 or so is not harmful to your motor in any significant way while towing. Your motor can easily maintain that RPM level for extended periods and just might be better off since you develop more HP and increase your coolant and oil flow at that higher engine speed. If you look at a dyno chart for your truck, you will see that you are not producing much usable power at RPM's below 2000, but just enough to keep your truck moving at highway speeds while empty in the most fuel efficient manner it can provide. That is the primary reason why OD is there.

On the other hand, if you had a diesel with the 4L80E tranny, you could tow up to certain weights in OD that in a gasser would require Drive. This is because a diesel produces gobs of torque at much lower engine speeds and uses a low stall speed torque converter that helps reduce hunting between gears when loaded.

You won't get good mileage, you won't get great acceleration, but you also won't be hurting your motor if you tow in Drive.

Cheers - Jonathan

_________________ The secret to not overheating your tranny (in 3 or OD) is the torque convertor needs to stay locked up. The torque converter generates large amounts of heat when it is not locked up. This usually means 3rd gear at slower freeway speeds, going into the wind, and/or pulling any kind of hill. Using OD while on flats is good if the converter can stay locked-up.

When I use 3rd gear and sustain 60mph, engine light comes on. I am assuming there is a temp sensor somewhere that clicks on and pokes me telling me I am running too hot (tranny/tc?). Alternatively if I run in OD and it's hilly my transmission freaks out and is constantly hunting between 3rd and 4th.

I use a combination of OD when flat, higher speeds need to be attained, but I drop it into 3rd when I am doing hills etc.

I see people with my exact truck (with trailer) screaming down the highway at 100km / hour (60 miles) every day. I wonder how they do it? Should I be able to run 3rd into 3000rpms for extended periods of time?

Mike

Good chance the drive axle gearing is different i.e. numerically higher. Respectfully submitted,

Loren Knighton Woodland, CA.

Under the hood since 1964 Member TRNI IATN