13mpg whahoo.
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Senior User
Joined: Nov 2007
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13mpg whahoo.
1989 F250 SC 4X4, 460, C6, w/32000 actual miles. Was getting 10mpg stock w/ new plugs, distributor, and wires. Did some mods, 3" cat back w/Cherrybomb Elite, K&N filter, all synthetic lubes, removed the restrictors/horns in the intake, new PVC valve, and new fan clutch. Used a GPS to verify odometer (my Odo reads 2 miles less per 100 miles than actual miles ie 100miles on odo is actually 102 miles and speedo reads 2 mph slow at 60mph ie speedo reads 60mph actual speed is 62mph according to my Garmin GPS)
Got right at 13mpg steady 60-62mph highway and light urban driving. Not the greatest but better than 10mpg.
I have read a lot about the air restrictors and was worried about the noise but I can not tell any difference in air intake noise. Hard to tell if they added anything to get up and go as I have not really gotten on it as I was more concerned with getting an accurate mpg reading.
Got right at 13mpg steady 60-62mph highway and light urban driving. Not the greatest but better than 10mpg.
I have read a lot about the air restrictors and was worried about the noise but I can not tell any difference in air intake noise. Hard to tell if they added anything to get up and go as I have not really gotten on it as I was more concerned with getting an accurate mpg reading.
Cargo Master
Joined: Oct 2008
Posts: 2,308
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From: Elyria, OH
i have an '89 f250 4x4 with a 351w a c6 tranny and 31,xxx actual miles. I cant get more than 9 mpg on the highway. I did, 3'' glasspack exhaust, full syenthetic fluids, K&N air cooler etc. any suggestions to what you may think is wrong. people are telling me that i should be getting around at least 11 city and close to 14-15 on the highway.
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Senior User
Joined: Nov 2007
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how is your fan clutch? You have low miles like me but mine was fully engaged all the time and I know that caused a lot of drag. I think just the fact that they are 20 years old causes them to quit working right. i am also running my tires at 60psi front and rear. I think these C6's may be bullet proof but sure could use an extra gear. Mine also has 3.55 gears.
I was happy to get 13mpg after getting 10 or less.
I was happy to get 13mpg after getting 10 or less.
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Senior User
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stock 235/85-16's. If your fan clutch is running locked in all the time than it does cause a lot of drag. You can tell because it sounds like a jet engine. When I replaced mine it was a huge difference in sound and i could feel that the motor was working less.
pedant
Joined: Jan 2008
Posts: 23,576
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From: EXTREME southwest CT
Congratulations!
I've got a T-19 and 4.10's on stock size E rated tires.
Turning 3k @ an indicated 60mph, 13 is attainable for me with a steady foot, all highway.
I can tell you from experience that a locked up fan clutch will not only kill your mileage, it will kill your water pump in short order on the highway...
Gotta be good for 20 horse at 4000 rpm.
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Cargo Master
Joined: Oct 2008
Posts: 2,308
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From: Elyria, OH
even with my stock 235/85/16's the mileage wasnt verymuch better. ill check out the fan issue tomorrow and see what we can do about that. the truck does kind of sound somewhat like a tractor motor, but i thought that may be due to a header gasket leak.
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Der Postmeister
Joined: Sep 2006
Posts: 6,859
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From: Long Beach, Calimexiforia
i have an '89 f250 4x4 with a 351w a c6 tranny and 31,xxx actual miles. I cant get more than 9 mpg on the highway. I did, 3'' glasspack exhaust, full syenthetic fluids, K&N air cooler etc. any suggestions to what you may think is wrong. people are telling me that i should be getting around at least 11 city and close to 14-15 on the highway.
Posting Guru
Joined: Aug 2007
Posts: 2,026
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From: Belle Mead NJ
If you have header leaks the outside air can get sucked in and caus ur exhaust to be lean. Thus the 02 sees this and makes a richer fuel mixture. So you could be wasting more gas. Id get on the header leak.
FTE Legend
Joined: Jun 2006
Posts: 31,930
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From: Ottawa, Ontario
There's your problem right there, you won't get any better milage without an OD tranny or a swap to 3.08 gears.
Cargo Master
Joined: Oct 2008
Posts: 2,308
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From: Elyria, OH
Do you think adding shorty or long tube head with a pair of high flow cats and a glasspack exhaust will help out at all? Also, what about a distributor up grade? I'm going to put a video on my other post showing how the truck will start up and rev pretty high and then it'll drop real low. It does this a few times and then returns to normal idle. Any idea on what may be causing this?
Cargo Master
Joined: Oct 2008
Posts: 2,308
Likes: 1
From: Elyria, OH
There was a system pass and then i got a 33. Egr valve. was told it wouldnt necessarily hurt my gas mileage.