Diesel F150 Forum banner
1 - 14 of 14 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter · #1 ·
Took delivery of my 2021 FX4 Platinum with 3.31 a couple months ago. Went with 3.31 because I rarely tow anything, BUT, since I've taken delivery we've been looking at travel trailers with GVWR 6000-6500 lbs. I have a 2" level and tires are slightly bigger than stock 275/60R20 up to 285/60R20. Will I have any issues towing in the mountains? Does locking out gears, which I've never done, help? Should I change my gears to 3.55 or 3.73? Truck has a tow rating of 10400 lbs. but I know there are lots of other factors to consider. Looking for thoughts and advice as I love the truck.
 

·
Administrator
Joined
·
822 Posts
@Roadking71865 - sounds like your requirements changed after purchase?

I am in-the-same-boat as you in terms of initial towing requirements = I have a 7x16 enclosed trailer for moving my tractors around.

You have the same trim levels as I do in my 2018 Platinum FX4. While Ford offers a bunch of F150 axle "choices" (and I use that term sarcastically), you really don't have a choice based on the Platinum Trim level and the addition of the FX4 package.

I summarized a lot of this in the Axle and Frame Research thread (read all the posts) and just by picking the 3.0L V6 Diesel engine, you limit your axle choices right out-of-the-gate to:
  • X27 Non-Limited-Slip 3.31
  • XL3 Electronic-Locking 3.31
  • XL9 Electronic-Locking 3.55
and once you check the box for the FX4 package, you are "locked in" (pun intended) to the XL3 Electronic 3.31.

My assumption is that if you ordered the FX4 package for off-roading, Ford stuck the shortest ratio axle in for maximizing off-road rocking climbing potential. This contradicts why Ford only offers the longest (4.10) axle option (which would be great for towing) in the Raptor, unless they assume all Raptor owners are doing Baja-style long distance desert racing.

I don't know what it would cost to swap out a different axle assembly, but my guess is that it wouldn't be worth it.

Since this is pretty much water-over-the-bridge, what you got is what you got, but I thought I'd explain from my previous research of the F150 Ordering Guide how you arrived at the axle you got.
 

·
Registered
Joined
·
3 Posts
Discussion Starter · #3 ·
@Roadking71865 - sounds like you requirements changed after purchase?

I am in-the-same-boat as you in terms of initial towing requirements = I have a 7x16 enclosed trailer for moving my tractors around.

You have the same trim levels as I do in my 2018 Platinum FX4. While Ford offers a bunch of F150 axle "choices" (and I use that term sarcastically), you really don't have a choice based on the Platinum Trim level and the addition of the FX4 package.

I summarized a lot of this in the Axle and Frame Research thread (read all the posts) and just by picking the 3.0L V6 Diesel engine, you limit your axle choices right out-of-the-gate to:
  • X27 Non-Limited-Slip 3.31
  • XL3 Electronic-Locking 3.31
  • XL9 Electronic-Locking 3.55
and once you check the box for the FX4 package, you are "locked in" (pun intended) to the XL3 Electronic 3.31.

My assumption is that if you ordered the FX4 package for off-roading, they stuck the shortest ratio axle in for maximizing off-road rocking climbing potential. This contradicts why they only offer longest (4.10) axle option (which would be great for towing) in the Raptor, unless they assume all Raptor owners are doing Baja-style long distance desert racing.

I don't know what it would cost to swap out a different axle assembly, but my guess is that it wouldn't be worth it.

Since this is pretty much water-over-the-bridge, what you got is what you got, but I thought I'd explain from my previous research of the F150 Ordering Guide how you arrived at the axle you got.
Took a look at the 10 speed gear ratios on 3.31 vs. 3.55 and they are all within 5.5-7%. Couldn't you achieve the same ratio on 3.31 as the 3.55 by locking out gears??
 

·
Super Moderator
Joined
·
559 Posts
I have one very unscientific comment- it doesn't change any of the numbers involved in towing but can we consider the nature of our little diesels? Towing with my 5.0 V8 is so different from towing with the 3.0 diesel. The diesel runs at a much lower RPM while the 5.0 moves the tach well up the scale.

By the way I have the 3.31 electronic locking in the diesel and the 3.55 in the 5.0.
 

·
Registered
2018 White extended cab 6.5 foot bed FX4 Tow package Lariat
Joined
·
64 Posts
Took delivery of my 2021 FX4 Platinum with 3.31 a couple months ago. Went with 3.31 because I rarely tow anything, BUT, since I've taken delivery we've been looking at travel trailers with GVWR 6000-6500 lbs. I have a 2" level and tires are slightly bigger than stock 275/60R20 up to 285/60R20. Will I have any issues towing in the mountains? Does locking out gears, which I've never done, help? Should I change my gears to 3.55 or 3.73? Truck has a tow rating of 10400 lbs. but I know there are lots of other factors to consider. Looking for thoughts and advice as I love the truck.
I have the same gear ratio and tow my 8,000 lbs 5th wheel without any real issues. Been over the Rocky Mountains with no problem. This is my opinion, for what it’s worth! Try it the way it is and if it’s not to your liking then change to the lower gears . In my experience it’s not needed unless you plan to do a lot of heavy towing almost daily. The mileage loss doesn’t justify being able to race up a mountain . As I have said I’ve been over the Rocky Mountains and was able to keep up with traffic over rabbit ears pass. Look the pass up and you will see for yourself, it’s not the highest but I didn’t have any problems whatsoever.
 

·
Registered
Joined
·
58 Posts
I have 3.31 gears 35x12.5 tires with leveling kit and larger rear blocks. I will be heading to lake George with the TT Labor Day weekend my trailer is in that 8 to 10 k range the trip is 200 miles/ 4hours one way I will report back with mileage mixed driving I currently get 18.5
 

·
Registered
Joined
·
16 Posts
Will I have any issues towing in the mountains? Does locking out gears, which I've never done, help? Should I change my gears to 3.55 or 3.73? Truck has a tow rating of 10400 lbs. but I know there are lots of other factors to consider.
You wont have any issues towing up the mountains, the 10 speed will drop to 8 or 7th gear. Remember that you have the power of 7.3 PowerStroke from F-350 minus a ton of weight.

I have 3.31 and I would stick with 3.31, you defiantly don't need 3.73. Diesel power curve is different from gasoline, low RPM is were the diesel is at.

"Does locking out gears, which I've never done, help" - you only need e-locker when you are off-road with bad traction such as mud or snow. Makes both rear tires spin at the same speed; when used on dry asphalt your truck should hop around since inner and outer tires have different turning radiuses. I would rather invest in front LSD than new gears.

I wouldn't be concerned about towing 7k RV, 10K max tow rating is different story.
 

·
Registered
Joined
·
16 Posts
My assumption is that if you ordered the FX4 package for off-roading, Ford stuck the shortest ratio axle in for maximizing off-road rocking climbing potential. This contradicts why Ford only offers the longest (4.10) axle option (which would be great for towing) in the Raptor, unless they assume all Raptor owners are doing Baja-style long distance desert racing.

Factor in the Raptor 35 inch tire diameter and 4.10 gears wouldn't that much different then stock truck with 3.73; 37 inch would be closer to 3.55
 

·
Registered
Joined
·
58 Posts
So the trip to Lake George went well there and back no issues what so ever towing. I cruised at 75 with the trailer most of the way no problems with hills but I did notice when using tow haul the truck liked to stay in 6th gear. I tried tow haul mode on the way there in normal mode on the way back both of Achieved the same gas mileage 10.5 MPG. Back to normal combine driving I am at 16.5. Seeing some of the other numbers on the site in my truck reaching 12,000 miles do you think I should change the filters or check into something else or maybe I just have a heavy foot but my mpg seems to be quite a bit lower than most.
 

·
Registered
2018 White extended cab 6.5 foot bed FX4 Tow package Lariat
Joined
·
64 Posts
So the trip to Lake George went well there and back no issues what so ever towing. I cruised at 75 with the trailer most of the way no problems with hills but I did notice when using tow haul the truck liked to stay in 6th gear. I tried tow haul mode on the way there in normal mode on the way back both of Achieved the same gas mileage 10.5 MPG. Back to normal combine driving I am at 16.5. Seeing some of the other numbers on the site in my truck reaching 12,000 miles do you think I should change the filters or check into something else or maybe I just have a heavy foot but my mpg seems to be quite a bit lower than most.
Maybe a little of that heavy foot syndrome going on. 10.5 seems on point while towing at 75 mph!! Anyway, do the math. Don’t rely on the on board calculator being accurate. Try resetting the calculator, and drive normal for a week or so without towing and see if that raises the mpg any. And compare with the hand calculations to see how accurate it is. 16.5 seems to be very low. I’m getting 22.5 on my daily commute.
 

·
Registered
Joined
·
126 Posts
You wont have any issues towing up the mountains, the 10 speed will drop to 8 or 7th gear. Remember that you have the power of 7.3 PowerStroke from F-350 minus a ton of weight.

I have 3.31 and I would stick with 3.31, you defiantly don't need 3.73. Diesel power curve is different from gasoline, low RPM is were the diesel is at.

"Does locking out gears, which I've never done, help" - you only need e-locker when you are off-road with bad traction such as mud or snow. Makes both rear tires spin at the same speed; when used on dry asphalt your truck should hop around since inner and outer tires have different turning radiuses. I would rather invest in front LSD than new gears.

I wouldn't be concerned about towing 7k RV, 10K max tow rating is different story.
"Locking out gears" has nothing to do with the rearend- it refers to limiting the highest gear the transmission can run in (9th, 8th, etc.).
 
1 - 14 of 14 Posts
Top