Cure for low MPG?
Cross-Country
Joined: Apr 2003
Posts: 89
Likes: 0
From: Montana
Thanks for the info grey, those calculators are handy. I have the ZF 5-speed, gear ratio in 5th is .76 for those other manual drivers out there.
Looks like my only options for the Dana 50 in the front is 3.73, doesn't appear to be that common, appears more people gear these down than up, not many places even sell the 3.73. I suppose that might be better for this truck than 3.55 anyway. I think that'll still drop my RPMs enough to get me in a more efficient range.
Ford couldn't have just gone with the more common Dana 60, oh no, they've got to be different...
Looks like my only options for the Dana 50 in the front is 3.73, doesn't appear to be that common, appears more people gear these down than up, not many places even sell the 3.73. I suppose that might be better for this truck than 3.55 anyway. I think that'll still drop my RPMs enough to get me in a more efficient range.
Ford couldn't have just gone with the more common Dana 60, oh no, they've got to be different...
Elder User
Joined: Nov 2004
Posts: 798
Likes: 0
Originally Posted by Lambo333
Thanks for the info grey, those calculators are handy. I have the ZF 5-speed, gear ratio in 5th is .76 for those other manual drivers out there.
Looks like my only options for the Dana 50 in the front is 3.73, doesn't appear to be that common, appears more people gear these down than up, not many places even sell the 3.73. I suppose that might be better for this truck than 3.55 anyway. I think that'll still drop my RPMs enough to get me in a more efficient range.
Ford couldn't have just gone with the more common Dana 60, oh no, they've got to be different...
Looks like my only options for the Dana 50 in the front is 3.73, doesn't appear to be that common, appears more people gear these down than up, not many places even sell the 3.73. I suppose that might be better for this truck than 3.55 anyway. I think that'll still drop my RPMs enough to get me in a more efficient range.
Ford couldn't have just gone with the more common Dana 60, oh no, they've got to be different...
Pull up the calculators.......dial in the height of a BFG 255/85R16........along with the 3.73 gears.......and I think you'll like the RPMs in the 65 - 70 MPH range.
And I agree with you the the 3.55 would probably be too high.....but I know many that are very happy with the 3.73 gearing. It's unfortunate that us 4x4 guys have to double the cost for a gearing change. That's alright though......I kinda like the idea of being able to get out of trouble, just about as fast as I get into it. LOL Take care.
Senior User
Joined: Jun 2003
Posts: 340
Likes: 0
From: Livonia
I have a 1999 f250 with a 8" lift and 37" tires...it has 3.73 gears and an 85hp chip...i get 11-13 in the city and i havent made a highway trip yet
but does that mileage sound normal for the size of the truck and chip?
BTW..it smokes black more than any other truck i have ever seen
but does that mileage sound normal for the size of the truck and chip?
BTW..it smokes black more than any other truck i have ever seen
Senior User
Joined: Jul 2005
Posts: 335
Likes: 0
From: BC Nevada
Sounds about right, Stick or auto? Hows the air filter situation? Also you've geared it way up with 37's I'd check the calc chart and see what your final ratio is now. Maybe the reason for lots of black smoke, got to give it lots of fuel to turn them meats. Your not going to see 18 MPG I would guess cause of them big tires and high lift. Be lucky to see 15 just a guess on my part. Hope I'm wrong for your sake.
LPR
LPR
Elder User
Joined: Nov 2004
Posts: 798
Likes: 0
Originally Posted by LONEPINERON
Sounds about right, Stick or auto? Hows the air filter situation? Also you've geared it way up with 37's I'd check the calc chart and see what your final ratio is now. Maybe the reason for lots of black smoke, got to give it lots of fuel to turn them meats. Your not going to see 18 MPG I would guess cause of them big tires and high lift. Be lucky to see 15 just a guess on my part. Hope I'm wrong for your sake.
LPR
LPR
Senior User
Joined: Jul 2005
Posts: 335
Likes: 0
From: BC Nevada
TOG, Is that what he would have to go to to make it like stock? I thought when you put bigger Tires on you had to go lower on gears to keep same ratio. Like on my jeep it has 4.10 and stock tires are 26" I added 33' tires so I need to go to 4.88's to keep the same ratio. So I believe he will need to go to 4.55's to keep the RPMs and speedo in line with stock.
Laughing Gas
Joined: Mar 2004
Posts: 751
Likes: 11
From: May Township, MN
The 99 F250 has 199K miles and the average mpg with no mods is 15-16 which is a slight drop over the past 6 years. The best mileage to date has been 19 mpg. If I get 17 mpg I'm pretty happy! 3.73 non limited slip
The 00 Excursion on the other hand has seen 20 mpg on paper three times and has averages 16-18 mpg. 3.73 limited slip. 146K miles.
It's strange to me the Excursion being about 1,000 heavier with the limited slip gets better mileage all the time. At 65 mph the Excursion runs about 100-200 more rpm's too. I've tried running the 33's on both vehicles for tens of thousands of miles and the results are still the same. The only thing I can think is the since the X is more stream line it does better.
The 00 Excursion on the other hand has seen 20 mpg on paper three times and has averages 16-18 mpg. 3.73 limited slip. 146K miles.
It's strange to me the Excursion being about 1,000 heavier with the limited slip gets better mileage all the time. At 65 mph the Excursion runs about 100-200 more rpm's too. I've tried running the 33's on both vehicles for tens of thousands of miles and the results are still the same. The only thing I can think is the since the X is more stream line it does better.
Elder User
Joined: Nov 2004
Posts: 798
Likes: 0
Originally Posted by LONEPINERON
TOG, Is that what he would have to go to to make it like stock? I thought when you put bigger Tires on you had to go lower on gears to keep same ratio. Like on my jeep it has 4.10 and stock tires are 26" I added 33' tires so I need to go to 4.88's to keep the same ratio. So I believe he will need to go to 4.55's to keep the RPMs and speedo in line with stock.
Yes, your correct. The calculator doesn't know Ford from Dana etc. It only looks at the numbers that are input. So, yes.....I agree it would probably have to be 4.55s. You might want to check out the link I directed him to......lots of good info there.
TOG
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Elder User
Joined: Nov 2004
Posts: 798
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Originally Posted by dougger222
The 99 F250 has 199K miles and the average mpg with no mods is 15-16 which is a slight drop over the past 6 years. The best mileage to date has been 19 mpg. If I get 17 mpg I'm pretty happy! 3.73 non limited slip
The 00 Excursion on the other hand has seen 20 mpg on paper three times and has averages 16-18 mpg. 3.73 limited slip. 146K miles.
It's strange to me the Excursion being about 1,000 heavier with the limited slip gets better mileage all the time. At 65 mph the Excursion runs about 100-200 more rpm's too. I've tried running the 33's on both vehicles for tens of thousands of miles and the results are still the same. The only thing I can think is the since the X is more stream line it does better.
The 00 Excursion on the other hand has seen 20 mpg on paper three times and has averages 16-18 mpg. 3.73 limited slip. 146K miles.
It's strange to me the Excursion being about 1,000 heavier with the limited slip gets better mileage all the time. At 65 mph the Excursion runs about 100-200 more rpm's too. I've tried running the 33's on both vehicles for tens of thousands of miles and the results are still the same. The only thing I can think is the since the X is more stream line it does better.
Senior User
Joined: Nov 2003
Posts: 200
Likes: 0
From: Lamar, SC
I am wishing there was a silver magic bullet to better mileage. I am with yall with keeping the rpms down, that seems to make a big difference with mine. And I always seem to run back into the ones that passed me going 75 and a stoplight somewhere. I am driving a focus right now daily, and saving the diesel for weekend driving. I love to drive that big nasty but it does love the diesel.
Senior User
Joined: Jul 2005
Posts: 335
Likes: 0
From: BC Nevada
Finally found the chart I was looking for and with the stock tires and 3.73 gears in OD you should be running around 1927 rpm. With the 37's you would be running at 1563. Which is lugging the engine. In order to get the RPM's back close to stock you will have to put 4.55s in there. As wel as around town your gearing is just too high kind of like starting off in second gear, takes a lot of throtal to turn them big tires. The chart is located at http://www.4wheelparts.com/4wp/help/...atio_chart.htm
now this doesn't figure in the OD so multiply the numbers by .71 and it will give you your RPM's.
Good Luck
LPR
now this doesn't figure in the OD so multiply the numbers by .71 and it will give you your RPM's.
Good Luck
LPR
Elder User
Joined: Mar 2003
Posts: 588
Likes: 0
From: AZ.
I was never happy with the 13 around town, 10 pulling a 26' trailer and the best on a 150 mile trip of 15 mpg, driving like a little old lady. I had it diagnosed and run on a dyno and everything came back as to being up to specs. I haven't installed my Edge Evolution yet but I hope to gain a mile or more. Everything is stock........Yet......
.. Down pipe and intake are in the very near future..
.. Down pipe and intake are in the very near future..