Th350 MPG question

I just learned last week or so that there was two versions of this trans. A lock up model and non lockup. I did some looking and found out that I don't have the lock up model in my truck but I should. Which explains the plug that has always hung beside the trans , not plugged in. Truck runs fine and dives perfect. But this got me to thinking, what do y'all think my mpg increase would be if I had the lock up version in my truck?

My truck is a stick 350/th350/205 . It's on 33" mud tires and has 3.08 gears. I get about 10mpg if I don't drive aggressive and can approach 12 if I baby the thing. It will get around 8mpg towing my 16ft dovetail car hauler trailer with my tractor, a few implements and an ATV....or basically about a 5000 pound load.

Just wondering. Not like I'm going to swap a perfectly working trans out but if it fails and I go to put another in I will probably look for a lock up to go back.

IMO... maybe 1 more mpg. Lockup doesn't lower your rpm down by a significant enough amount to make a big difference.

I would agree. It might make bigger difference strictly highway mileage. Assuming you have enough rear gear ratio, a 4L60 would be a nice upgrade. But only if/when your current trans dies.

Green79Scottsdale said:

IMO... maybe 1 more mpg. Lockup doesn't lower your rpm down by a significant enough amount to make a big difference.

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This was actually my exact thoughts.

I would say 1 mpg with a strong tail wind.

With 3.08 gears and 33" tires you might not see much improvement with a lock-up 350. You are already running a really low cruise RPM, which probably puts the engine out of its optimal torque curve.

Bruce

When the convertor is locked, you save creating extra heat and wear and tear. Not a big deal in a T350. Much more important in a 700.

Your 308 gears are already to high anyway, a locking convertor will make things worse. You would get better mpg with 31" tires.

80BrownK10 said:

do y'all think my mpg increase would be if I had the lock up version in my truck?

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No, I dont think that.
I believe locking and unlocking with 308s will cause exponentially more harm than good.
aint broke dont fix it?


I think I would be happy as a pig in **** if that combo got 10mpg for me out of that truck.

75gmck25 said:

With 3.08 gears and 33" tires you might not see much improvement with a lock-up 350. You are already running a really low cruise RPM, which probably puts the engine out of its optimal torque curve.

Bruce

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I seem to have plenty of torque while cruising down the highway. Now pulling a trailer and have to accelerate of course it drops to second.

Rusty Nail said:

No, I dont think that.
I believe locking and unlocking with 308s will cause exponentially more harm than good.
aint broke dont fix it?


I think I would be happy as a pig in **** if that combo got 10mpg for me out of that truck.

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Well I get 10mpg just driving conservative. Like I said pulling a 16ft 5000pound trailer gets me around 8. Since my speedometer adapter broke the odometer doesn't work anymore. Well it does but it's about 30% low right now.

This is a lighter trailer than I will have sometimes. I will have another implement on sometimes like the disk harrow up front and tractor behind it with the bush hog. But it doesn't make any difference gets basically the same MPG.

75gmck25 said:

With 3.08 gears and 33" tires you might not see much improvement with a lock-up 350. You are already running a really low cruise RPM, which probably puts the engine out of its optimal torque curve.

Bruce

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I agree with this 100%

80BrownK10 said:

Well I get 10mpg just driving conservative. Like I said pulling a 16ft 5000pound trailer gets me around 8. Since my speedometer adapter broke the odometer doesn't work anymore. Well it does but it's about 30% low right now.

This is a lighter trailer than I will have sometimes. I will have another implement on sometimes like the disk harrow up front and tractor behind it with the bush hog. But it doesn't make any difference gets basically the same MPG.

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Wow, I'm surprised that squats so much with a relatively light load. Or is it just the angle of the picture?

I got 8mpg with a wore out 350/rebuilt 700r4/31" tires/3.08 gears. I'd be proud if I got 10 outta mine with a TH350.

bucket said:

I agree with this 100%



Wow, I'm surprised that squats so much with a relatively light load. Or is it just the angle of the picture?

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I think some is the springs are tired?

The ATV in the bed is about 500 pounds. The tractor weighs about 2000 pounds with a 500 pound bush hog . The whole tractor is basically over or infront of the front axle of the trailer.

That trailer I guess is what 1500ish pounds. The tongue weight empty on that trailer is probably 200-250 pounds empty.

I could be wrong because every setup is different. My flatbed and dump trailers have the axles offset slightly to the rear. I like just a slight bias of weight forward of the axles. Your tractor looks a bit far forward.

Back to the topic...with a lighter duty trans, I wouldn’t want lock up with the tall gear combo you have. It would probably go in and out of lockup constantly and heat it up. Unless you live somewhere flat and the th350c has the D without lockup position like some OD transmissions.

edit: accidentally typed that the tractor looked a bit far back when I meant forward.