another mpg problem
Thread Starter
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Freshman User
Joined: Jun 2002
Posts: 36
Likes: 0
another mpg problem
Here we go,I just went on an 850 mile trip and only got 9.8 mpg.
My trucks a 1994 F-150,
4.9, K&N air filter
3" flowmaster from the cat back
5 speed, 3.55 gears
Have a cap on the back 31x10.50-15 back tires 235x75-15 front.
I had my radiator rodded for a over heating problem and put a 160 thermostat in it.
Truck has 56000 miles on change oil every 3000 miles tune-up every 25000 miles.New the truck got 12-15 mpg, tested for vac. leaks OK
Could the 160 thermostat be telling the computer false info?
Can some one give me the magic fix Thanks
My trucks a 1994 F-150,
4.9, K&N air filter
3" flowmaster from the cat back
5 speed, 3.55 gears
Have a cap on the back 31x10.50-15 back tires 235x75-15 front.
I had my radiator rodded for a over heating problem and put a 160 thermostat in it.
Truck has 56000 miles on change oil every 3000 miles tune-up every 25000 miles.New the truck got 12-15 mpg, tested for vac. leaks OK
Could the 160 thermostat be telling the computer false info?
Can some one give me the magic fix Thanks
Elder User
Joined: Jan 2000
Posts: 966
Likes: 2
From: Crooked River Ranch, OR
another mpg problem
Unless you installed an aftermarket chip in the computor which calls for a cooler thermostat 160 would keep you in the overly rich mode. Try running a 180 degree instead. Your 31 X 10.5's won't help either...they are a drag on a small engine like the 4.9
Deen
Deen
New User
Joined: Mar 2002
Posts: 11
Likes: 0
another mpg problem
My family and I just took a long trip in our 96 xtdcab 4.9 5 speed, 3.55 axle 2wd. Most of the trip was interstate, but a fair bit was rural roads. The wife tends to pack everything, and the kids had their stuff. We got 17 MPG, which I was happy with considering the mountains and rural roads. The truck is mostly stock, just advanced the timing and removed the snorkel that leads into the airbox. The folks we visited are misguided chevy fans, and they were very impressed with the torque of the 4.9.
Good Luck!!!!
Good Luck!!!!
Post Fiend
Joined: Nov 2001
Posts: 14,947
Likes: 6
From: Topsfield, MA
another mpg problem
Actually, the 31" tires will increase mileage because it'll make the RPMs lower, despite the few extra lbs of weight. Could be many things, but you are at a loss for power. Could be a plugged cat, maybe need a new oxy sensor, I'd check the codes from the computer and see what you come out with.
Primary rig is Green Thunder:
95' F-150 XLT 4x4, 302, 5 spd, MSD 6A, Flowmaster American Thunder Exhaust, Sunroof, Clear corners w/ Diamond headlights, CD player with 2 10" subs and some 32" BFG Muds
.
Check out my Gallery for a look-see.
Then theres:
99' Mustang GT 4.6L
88' F-250 Heavyduty 4x4 351/c6
95' Mercury Cougar 4.6L V-8
80' E-350 300/6 with a
3 spd column shifter. Weighs around 7,000lbs w. 65mph top speed, who wants to race me!
Primary rig is Green Thunder:
95' F-150 XLT 4x4, 302, 5 spd, MSD 6A, Flowmaster American Thunder Exhaust, Sunroof, Clear corners w/ Diamond headlights, CD player with 2 10" subs and some 32" BFG Muds
.Check out my Gallery for a look-see.
Then theres:
99' Mustang GT 4.6L
88' F-250 Heavyduty 4x4 351/c6
95' Mercury Cougar 4.6L V-8
80' E-350 300/6 with a
3 spd column shifter. Weighs around 7,000lbs w. 65mph top speed, who wants to race me!
Thread Starter
|
Freshman User
Joined: Jun 2002
Posts: 36
Likes: 0
another mpg problem
Thanks for all the input. I put a 195 stat in the truck Taking a trip to a car show today.
To ansure some of the question asked,
the truck has great power (I pull a 25'travel trailer with it)
the back tires are only about 1 1/2" taller than the fronts
I'll write back with milage again thanks!!!
To ansure some of the question asked,
the truck has great power (I pull a 25'travel trailer with it)
the back tires are only about 1 1/2" taller than the fronts
I'll write back with milage again thanks!!!
Post Fiend
Joined: Nov 2001
Posts: 14,947
Likes: 6
From: Topsfield, MA
another mpg problem
Those bigger tires will decrease the RPMs on the highway by about 150-200, therefore saving gas.
Primary rig is Green Thunder:
95' F-150 XLT 4x4, 302, 5 spd, MSD 6A, Flowmaster American Thunder Exhaust, Sunroof, Clear corners w/ Diamond headlights, CD player with 2 10" subs and some 32" BFG Muds .
Check out my Gallery for a look-see.
Then theres:
99' Mustang GT 4.6L
88' F-250 Heavyduty 4x4 351/c6
95' Mercury Cougar 4.6L V-8
80' E-350 300/6 with a
3 spd column shifter. Weighs around 7,000lbs w. 65mph top speed, who wants to race me!
Primary rig is Green Thunder:
95' F-150 XLT 4x4, 302, 5 spd, MSD 6A, Flowmaster American Thunder Exhaust, Sunroof, Clear corners w/ Diamond headlights, CD player with 2 10" subs and some 32" BFG Muds
.Check out my Gallery for a look-see.
Then theres:
99' Mustang GT 4.6L
88' F-250 Heavyduty 4x4 351/c6
95' Mercury Cougar 4.6L V-8
80' E-350 300/6 with a
3 spd column shifter. Weighs around 7,000lbs w. 65mph top speed, who wants to race me!
Trending Topics
Elder User
Joined: May 2001
Posts: 692
Likes: 1
From: Coon Rapids, MN
another mpg problem
Just remember to calculate the difference in tire diameters when you figure your gas mileage or it will seem the same or a tad lower. 9.8 is quite low, im getting 11 in town and last fall I was getting 14-16 on the highway.
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Freshman User
Joined: May 2002
Posts: 32
Likes: 0
From: seattle usa
another mpg problem
put your tail gate down .i did this to mine on a 280 mile trip and saved a quater tank both ways,plus try to keep it at 60 because they were designed to max gas millage at 55 during the gas crunch during the 80s.
Post Fiend
Joined: Nov 2001
Posts: 7,698
Likes: 4
From: Neenah, Wisconsin
another mpg problem
The bigger tires might not improve gas milage...mustang...your on the right track but you forgot about something. The larger tire will lower rpms...i won't argue that with you there. But you forgot something that will change the gas milage idea. Your engine was built to produce torque in a specific rpm range. Ford was smart enough to design a gear reduction set..tranny and axle...with the right tire size to produce optimal gas milage and power...now when you put too large of a tire on you effectivly reduce the final drive ratio. The engine must work harder to do move the tire around. Now try this..idle your engine for an hour at 1000 rpms...now go drive your truck for an hour and set the cruise at around 40 mph..this should be roughly 1000 rpms.....now your going to use way more gas actually driving it...this is because the engine has to work harder. So all said....putting a bigger tire on will affect gas milage.
Ryan
Ryan
New User
Joined: Jun 2002
Posts: 10
Likes: 0
From: Westbrook USA
another mpg problem
>The bigger tires might not improve gas
>milage...mustang...your on the right track but you forgot
>about something. The larger tire will lower rpms...i won't
>argue that with you there. But you forgot something that
>will change the gas milage idea. Your engine was built to
>produce torque in a specific rpm range. Ford was smart
>enough to design a gear reduction set..tranny and
>axle...with the right tire size to produce optimal gas
>milage and power...now when you put too large of a tire on
>you effectivly reduce the final drive ratio. The engine
>must work harder to do move the tire around. Now try
>this..idle your engine for an hour at 1000 rpms...now go
>drive your truck for an hour and set the cruise at around 40
>mph..this should be roughly 1000 rpms.....now your going to
>use way more gas actually driving it...this is because the
>engine has to work harder. So all said....putting a bigger
>tire on will affect gas milage.
>
>Ryan
I agree. If the tranny is an automatic, shift paterns change as well. A four foot tractor tire does less rpm's a mile, but requires more power to turn it through unchanged, stock gearing. That means more fuel.
>milage...mustang...your on the right track but you forgot
>about something. The larger tire will lower rpms...i won't
>argue that with you there. But you forgot something that
>will change the gas milage idea. Your engine was built to
>produce torque in a specific rpm range. Ford was smart
>enough to design a gear reduction set..tranny and
>axle...with the right tire size to produce optimal gas
>milage and power...now when you put too large of a tire on
>you effectivly reduce the final drive ratio. The engine
>must work harder to do move the tire around. Now try
>this..idle your engine for an hour at 1000 rpms...now go
>drive your truck for an hour and set the cruise at around 40
>mph..this should be roughly 1000 rpms.....now your going to
>use way more gas actually driving it...this is because the
>engine has to work harder. So all said....putting a bigger
>tire on will affect gas milage.
>
>Ryan
I agree. If the tranny is an automatic, shift paterns change as well. A four foot tractor tire does less rpm's a mile, but requires more power to turn it through unchanged, stock gearing. That means more fuel.
Senior User
Joined: May 2002
Posts: 102
Likes: 0
From: Show Low AZ
another mpg problem
Did your truck come with 235/75/15's stock? The tall tires in the back can throw off your indicated mileage, making your odometer read lower miles than what was actually travelled if you did not recalibrate the speedometer. Will also make your speedometer read low, f'r instance it says 65 but you're really going 70 per the state trooper clocking you.
Postmaster
Joined: Jun 1999
Posts: 2,719
Likes: 1
From: Lee's Summit MO
another mpg problem
No actually, PaintedDesert56, it's the opposite. Larger tires will make your speedo go faster. Smaller tires have a smaller diameter than larger tires.
Going 70mph according to your speedo is more like actually 68.9mph.
Going 70mph according to your speedo is more like actually 68.9mph.
Senior User
Joined: Aug 2002
Posts: 104
Likes: 0
From: Madison USA
another mpg problem
WRONG!!! 
bigger tires make your speedo read slower. You go further on the same revolution of a big tire versus a smaller tire. Therefore, the drivetrain doesn't turn as fast as it did with smaller tires at the same VEHICLE SPEED. I agree, the with original tires being 235/75R15, and changing to 31x10.5x15, your speedo will say 65, and you will be going about 70. Believe me, I know, as well as the rest of the guys. Not to mention how that state trooper's radar gun knows. Of course, this was in a 55 limit..oops
bigger tires make your speedo read slower. You go further on the same revolution of a big tire versus a smaller tire. Therefore, the drivetrain doesn't turn as fast as it did with smaller tires at the same VEHICLE SPEED. I agree, the with original tires being 235/75R15, and changing to 31x10.5x15, your speedo will say 65, and you will be going about 70. Believe me, I know, as well as the rest of the guys. Not to mention how that state trooper's radar gun knows. Of course, this was in a 55 limit..oops
Elder User
Joined: Feb 2002
Posts: 755
Likes: 1
From: Campbell, California
another mpg problem
>Those bigger tires will decrease the RPMs on the highway by
>about 150-200, therefore saving gas.
>
Not always true. Putting on larger tires will change the overall ratio of your drive line. Yes you will be running lower RPM, but you've also changed your power band with respect to the stock setup. Lower RPMs also means less torque and horsepower. So to compensate, some what, you step on the gas a little harder and a little longer. The best way to compensate for large tires is the change the gearing in the diff to bring the engine back into the powerband. In Toy man's case, I don't think his problem is the tires more then it is the 160 thermostat.
>about 150-200, therefore saving gas.
>
Not always true. Putting on larger tires will change the overall ratio of your drive line. Yes you will be running lower RPM, but you've also changed your power band with respect to the stock setup. Lower RPMs also means less torque and horsepower. So to compensate, some what, you step on the gas a little harder and a little longer. The best way to compensate for large tires is the change the gearing in the diff to bring the engine back into the powerband. In Toy man's case, I don't think his problem is the tires more then it is the 160 thermostat.