brulaz

Suppose you could use more gas lugging up a hill in 6th compared to doing it with higher revs in 5th.

But the tranny is so smart, you would think it takes that into consideration?

Think I'll give it a try.

rancherlee

locking out 6th makes perfect sense to me on saving fuel. The LESS the engine needs to rely on boost the better mileage it will get. When under boost the computer feeds it extra fuel to keep combustion temps under control. With 3.5L of displacement there isn't too much more parasitic drag revving the engine a bit, Also would probably help with engine longevity as well.

humblerb

While this makes sense, I never thought about it before.
I'm going to give it a trial on my next trip. We usually drive 60-75 minutes one-way, so up with 6th locked out and back in 6th, I should be able to see for myself.

EDIT for a quick question. Locking out 6th keeps the boost from burning more fuel. Won't the turbos kick in when in 5th? Just thinking out-loud, so to speak. I'll still give it a trial next time out.

flixden

I've seen it happen, even when not towing.
There is a very long, steady incline hill on my way back home from work. Not towing, empty truck, just me as the driver, the truck will go up that hill at the speed limit (50mph) in 6th gear. I have tested it a hundred times, always the same: I set cruise to exactly 50, and half way up the hill, I lock out 6th. The truck shifts down to 5th, and the green fuel consumption bar jumps up from just under to just over the lower white horizontal line.

brulaz

I tried locking out 6th today when towing 4000#. It was hard to find a steady slope where I could cut out 6th and be sure the slope did not change. Also it was very windy which made the instantaneous mileage bounce around a bit. A couple of times I thought there might have been a drop in instantaneous mileage in 5th, but other times ...

On a long ~ level stretch I could see no diff in instantaneous mileage. This was with cruise on 100km/h (62 mph). In sixth that was ~1650 rpm, in 5th rpm was 2100.

Anyway, basically spent the whole day in 5th, and it was a nice ride at 2100 rpm. No 6 to 5 downshifting on the hills. Got some of the best mileage ever, but that was the tailwind.

Think I'll keep this up and see how it works out long term. Of course I've also changed the tires last week so that'll screw up any long-term comparisons.

mikenannie

So, if you can get better mileage in 5th, either pulling a trailer or not, then why would Ford put a 6th gear in this truck?

Seems to me that they would want the EPA to post better MPG on the sticker.

Interesting discussion.

mikenannie

An answer to my own question - Maybe for the 5.0L owners?

Jerryb1973

If you are in 6th but not in boost (1650RPM) seems there would be no way 5th w/no boost (2100RPM) would give you better MPG. When you run a higher RPM, isnt the engine working harder? I have no personal experience, but wondering if the experts here can help me understand.--Thanks in advance.

brulaz

Don't think you'll get better mileage locking out 6th unless you're towing/hauling some weight. Flixden didn't. I always use 6th when not towing.

And it may not be in all circumstances even when you are towing. On the flat and level I would expect 6th to give better mileage, but I didn't see any difference on the instantaneous mileage.

But you really have to make the same run a bunch of times with the same load and speed, both with 6th cut out and not, and compare the mileages. Things like wind and speed can have a big effect on the mileage of a single run.

brulaz

My Boost meter showed boost in 6th going up a hill at 62mph and 1650rpm.

Isn't the main reason the Ecoboost has two turbos is to start boost at low rpms and increase low-end torque?

EDIT: But don't know if the boost was different in 6th at 1650rpm versus 5th at 2100rpm. Does more boost always equal less mpg?