Leaf spring codes and what they mean....
4wd Low
Joined: Oct 2012
Posts: 14
Likes: 0
Your wagon looks great! 
Was the entire 410 miles driven at 70 MPH? I’ve made the 450 mile drive from Philly to/from Columbus OH which is all highway with the exception of a few interchanges and have gotten 14.5 MPG with the cruise set at 65 MPH. My EX has 4.88 gears with 35” highway tread tires that nets an effective 4.39 ratio, it also has Banks headers and runs the 5Star 89 octane performance tune with matching gas.
Was the entire 410 miles driven at 70 MPH? I’ve made the 450 mile drive from Philly to/from Columbus OH which is all highway with the exception of a few interchanges and have gotten 14.5 MPG with the cruise set at 65 MPH. My EX has 4.88 gears with 35” highway tread tires that nets an effective 4.39 ratio, it also has Banks headers and runs the 5Star 89 octane performance tune with matching gas.
4wd Low
Joined: Oct 2012
Posts: 14
Likes: 0
Your wagon looks great!
Was the entire 410 miles driven at 70 MPH? I’ve made the 450 mile drive from Philly to/from Columbus OH which is all highway with the exception of a few interchanges and have gotten 14.5 MPG with the cruise set at 65 MPH. My EX has 4.88 gears with 35” highway tread tires that nets an effective 4.39 ratio, it also has Banks headers and runs the 5Star 89 octane performance tune with matching gas.
Was the entire 410 miles driven at 70 MPH? I’ve made the 450 mile drive from Philly to/from Columbus OH which is all highway with the exception of a few interchanges and have gotten 14.5 MPG with the cruise set at 65 MPH. My EX has 4.88 gears with 35” highway tread tires that nets an effective 4.39 ratio, it also has Banks headers and runs the 5Star 89 octane performance tune with matching gas.
Fleet Mechanic
Joined: Mar 2023
Posts: 1,598
Likes: 939
Really, that’s the best you’ve seen?
I get better than that while towing my 30ft camper at Texas highway speeds.
Do the gassers Excursions really get that low of fuel mileage on the regular?
…
4wd Low
Joined: Oct 2012
Posts: 14
Likes: 0
Moderator
Joined: Jul 2010
Posts: 12,058
Likes: 1,565
From: Media PA
Were you towing the TT in OD? If so did it downshift frequently? Was it a box shaped TT or another Airstream like you mentioned earlier?
I know that your EX is just now at 44K miles, but have the plugs and boots been changed? 20 year old rubber plug boots could be bleeding voltage and causing weak spark or even intermittent misses.
I tow a TT at twice the weight of what you mentioned and see the same or better fuel mileage, have done 9.5 MPG on three trips over 400 miles, typically an all highway tow would give about 8.5 to 9 MPG at 65 MPH on fairly flat terrain. The 89 octane performance tune I run really reduces the amount of downshifts out of OD, which helps with the fuel economy and as I mentioned earlier my highway tread tires should also have an advantage over A/Ts like it looks you have. And maybe the Banks headers and free flowing exhaust helps some too, lots of little things can add up. But my lift and fatter tires should be a negative…… And it’s really hard to accurately compare on tow over a certain route to another, too many variables.
4wd Low
Joined: Oct 2012
Posts: 14
Likes: 0
Interesting that 5MPH slower netted almost .5 less MPG.
Were you towing the TT in OD? If so did it downshift frequently? Was it a box shaped TT or another Airstream like you mentioned earlier?
I know that your EX is just now at 44K miles, but have the plugs and boots been changed? 20 year old rubber plug boots could be bleeding voltage and causing weak spark or even intermittent misses.
I tow a TT at twice the weight of what you mentioned and see the same or better fuel mileage, have done 9.5 MPG on three trips over 400 miles, typically an all highway tow would give about 8.5 to 9 MPG at 65 MPH on fairly flat terrain. The 89 octane performance tune I run really reduces the amount of downshifts out of OD, which helps with the fuel economy and as I mentioned earlier my highway tread tires should also have an advantage over A/Ts like it looks you have. And maybe the Banks headers and free flowing exhaust helps some too, lots of little things can add up. But my lift and fatter tires should be a negative…… And it’s really hard to accurately compare on tow over a certain route to another, too many variables.
Were you towing the TT in OD? If so did it downshift frequently? Was it a box shaped TT or another Airstream like you mentioned earlier?
I know that your EX is just now at 44K miles, but have the plugs and boots been changed? 20 year old rubber plug boots could be bleeding voltage and causing weak spark or even intermittent misses.
I tow a TT at twice the weight of what you mentioned and see the same or better fuel mileage, have done 9.5 MPG on three trips over 400 miles, typically an all highway tow would give about 8.5 to 9 MPG at 65 MPH on fairly flat terrain. The 89 octane performance tune I run really reduces the amount of downshifts out of OD, which helps with the fuel economy and as I mentioned earlier my highway tread tires should also have an advantage over A/Ts like it looks you have. And maybe the Banks headers and free flowing exhaust helps some too, lots of little things can add up. But my lift and fatter tires should be a negative…… And it’s really hard to accurately compare on tow over a certain route to another, too many variables.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
Top 6 Best Deals Available on New Fords & Lincolns Right Now
Brett Foote
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Verdad Gallardo
Top 10 Fords at 2026 Carlisle Ford Nationals
Joe Kucinski
3 Best / 3 Worst Parts of Modern Ford Ownership
Brett Foote
10 Amazing Upgrades That Solve Common Ford Truck Owner Headaches
Pouria Savadkouei
Every 2026 Ford Engine Explained
Brett Foote
10 Ugly Ford Trucks That We Still Kinda Love
Joe Kucinski
10 Things Every Truck Owner NEEDS (2026 Edition)
Michael S. Palmer
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Verdad Gallardo
Fleet Mechanic
Joined: Mar 2023
Posts: 1,598
Likes: 939
With both engines I’d routinely get 17-18 mpg unloaded. The Cummins really doesn’t get much, if any, better fuel mileage than the 6.0 did.
Towing my 30 foot RV travel trailer around I get low 13s usually ( that’s with the Cummins, never trusted the 6.0 enough to take the travel trailer out very far). And I drive/ tow at the speed limit/ with the flow of traffic, which the speed limit in some parts of west Texas is 80mph, with 75 mph speed limits being really common everywhere.
…
5th Wheeling
Joined: Oct 2016
Posts: 40
Likes: 2
This chart doesn't seem to make sense. My 99 F-350 4x4 DRW C&C v10, sticker has SPR: TD with front axle 4,400lb and rear 8,024lb. T should be closer to 2,200lb? D at 4,000+lb may be close.
Spring........Capacity.....Rate lbs/".....Max travel.....V-10 change.....PSD change
D (PSD).....4700lbs.......380 lb/".........5.14"...........+0.33".............0 .00"
T codes.....4400lbs.......390 lb/".........4.63"...........+1.42"............+1 .11"
Spring........Capacity.....Rate lbs/".....Max travel.....V-10 change.....PSD change
D (PSD).....4700lbs.......380 lb/".........5.14"...........+0.33".............0 .00"
T codes.....4400lbs.......390 lb/".........4.63"...........+1.42"............+1 .11"
Moderator
Joined: Jul 2010
Posts: 12,058
Likes: 1,565
From: Media PA
This chart doesn't seem to make sense. My 99 F-350 4x4 DRW C&C v10, sticker has SPR: TD with front axle 4,400lb and rear 8,024lb. T should be closer to 2,200lb? D at 4,000+lb may be close.
Spring........Capacity.....Rate lbs/".....Max travel.....V-10 change.....PSD change
D (PSD).....4700lbs.......380 lb/".........5.14"...........+0.33".............0 .00"
T codes.....4400lbs.......390 lb/".........4.63"...........+1.42"............+1 .11"
Spring........Capacity.....Rate lbs/".....Max travel.....V-10 change.....PSD change
D (PSD).....4700lbs.......380 lb/".........5.14"...........+0.33".............0 .00"
T codes.....4400lbs.......390 lb/".........4.63"...........+1.42"............+1 .11"
Makes perfect sense, your front T codes with a GAWR of 4400 lbs matches the charts T code listing of 4400 lbs. The capacity on the chart is for the pair of springs, not individually, just like how the door jamb sticker lists them in the GAWR.
And the D codes on the chart are front leaf springs, all of the springs listed on the chart are front springs as explained above, I don’t have a similar chart for the rear springs. But obviously for ‘99 D codes on rears are 8024 lbs for the pair. Also, cab chassis trucks may have completely different rear springs than pickups, I know that at least later models had different length rear springs between pickups and c&c trucks.
Thread
Thread Starter
Forum
Replies
Last Post