What am I doing wrong?
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Cargo Master
Joined: Oct 2010
Posts: 2,339
Likes: 32
From: Lost In a Pit of Despair
What am I doing wrong?
Well I've been driving my highboy around for a couple weeks now, and I have to say, I'm slightly dismayed by the mpg I've been getting.
I read all around that people with the 300/np435 combination were getting anywhere from 16-20 mpg based on driving habits and front/rear gearing, even in the highboys. So far, I've gotten 12.7, 13.4, and 11.5 mpg. Most of my driving is highway, with an average of 55 mph. Twice a week I go off island for college, where I see brief periods on the freeway around 70 mph. Now the most recent mpg might have been affected by a short (~5 miles) trip with a 600lb compressor loaded in the bed. I'm not expecting for this to get super high mpg, but I at least hoped it would be a little better..
As far as measuring, I fill up the cab tank (19 gal), mark the OD reading, and drive until I run out of gas and mark the OD reading again. Then I simply take the difference in the OD readings and divide by 19.
-Jameson
I read all around that people with the 300/np435 combination were getting anywhere from 16-20 mpg based on driving habits and front/rear gearing, even in the highboys. So far, I've gotten 12.7, 13.4, and 11.5 mpg. Most of my driving is highway, with an average of 55 mph. Twice a week I go off island for college, where I see brief periods on the freeway around 70 mph. Now the most recent mpg might have been affected by a short (~5 miles) trip with a 600lb compressor loaded in the bed. I'm not expecting for this to get super high mpg, but I at least hoped it would be a little better..
As far as measuring, I fill up the cab tank (19 gal), mark the OD reading, and drive until I run out of gas and mark the OD reading again. Then I simply take the difference in the OD readings and divide by 19.
-Jameson
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Don't try to calculate the mileage like that.
Fill it up, record the mileage. Drive it until you have a 1/4 tank or less. Fill it up again and record the gallons it took. Record the mileage.
Deduct the original mileage from the last mileage.
Take the mileage driven and divide by number of gallons used, that's your MPG.
Example:
You fill up and the mileage is 59,763.4 you drive it and fill up again, this time the mileage is 60,024.8 and you filled up with 21.6 gallons.
60,024.8
-59,763.4= 261.4
You drove 261.4 miles and used 21.6 gallons so that's 261.4 divided by 21.6=12.1 MPG.
Fill it up, record the mileage. Drive it until you have a 1/4 tank or less. Fill it up again and record the gallons it took. Record the mileage.
Deduct the original mileage from the last mileage.
Take the mileage driven and divide by number of gallons used, that's your MPG.
Example:
You fill up and the mileage is 59,763.4 you drive it and fill up again, this time the mileage is 60,024.8 and you filled up with 21.6 gallons.
60,024.8
-59,763.4= 261.4
You drove 261.4 miles and used 21.6 gallons so that's 261.4 divided by 21.6=12.1 MPG.
Thread Starter
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Cargo Master
Joined: Oct 2010
Posts: 2,339
Likes: 32
From: Lost In a Pit of Despair
Don't try to calculate the mileage like that.
Fill it up, record the mileage. Drive it until you have a 1/4 tank or less. Fill it up again and record the gallons it took. Record the mileage.
Deduct the original mileage from the last mileage.
Take the mileage driven and divide by number of gallons used, that's your MPG.
Example:
You fill up and the mileage is 59,763.4 you drive it and fill up again, this time the mileage is 60,024.8 and you filled up with 21.6 gallons.
60,024.8
-59,763.4= 261.4
You drove 261.4 miles and used 21.6 gallons so that's 261.4 divided by 21.6=12.1 MPG.
Fill it up, record the mileage. Drive it until you have a 1/4 tank or less. Fill it up again and record the gallons it took. Record the mileage.
Deduct the original mileage from the last mileage.
Take the mileage driven and divide by number of gallons used, that's your MPG.
Example:
You fill up and the mileage is 59,763.4 you drive it and fill up again, this time the mileage is 60,024.8 and you filled up with 21.6 gallons.
60,024.8
-59,763.4= 261.4
You drove 261.4 miles and used 21.6 gallons so that's 261.4 divided by 21.6=12.1 MPG.
Lead Driver
Joined: Dec 2012
Posts: 7,870
Likes: 47
From: Tennessee
In the 80's I had a truck that got a solid 12.5 mpg . Loaded , empty , up , down hill . It was solid as a rock ! My next truck verried from 14 to 23 mpg ! Calculating the same way ! My current F100 gets 15 to 16 mpg ( no freeway ) .
Cross-Country
Joined: Dec 2004
Posts: 67
Likes: 11
From: Union, WV
I agree with mike - the problem is that you can't tell exactly how much fuel you put in unless you refill it to a known level - i.e. full.
But otherwise as far as mileage goes, a lot of it comes with tuning. Vacuum connections/hoses are the first offenders. Ignition timing and points gap/dwell (if applicable) can affect it too, as well as carb settings. Then plugs, wires, etc etc. Vacuum would be the first step for me.
But otherwise as far as mileage goes, a lot of it comes with tuning. Vacuum connections/hoses are the first offenders. Ignition timing and points gap/dwell (if applicable) can affect it too, as well as carb settings. Then plugs, wires, etc etc. Vacuum would be the first step for me.
Thread Starter
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Cargo Master
Joined: Oct 2010
Posts: 2,339
Likes: 32
From: Lost In a Pit of Despair
I agree with mike - the problem is that you can't tell exactly how much fuel you put in unless you refill it to a known level - i.e. full.
But otherwise as far as mileage goes, a lot of it comes with tuning. Vacuum connections/hoses are the first offenders. Ignition timing and points gap/dwell (if applicable) can affect it too, as well as carb settings. Then plugs, wires, etc etc. Vacuum would be the first step for me.
But otherwise as far as mileage goes, a lot of it comes with tuning. Vacuum connections/hoses are the first offenders. Ignition timing and points gap/dwell (if applicable) can affect it too, as well as carb settings. Then plugs, wires, etc etc. Vacuum would be the first step for me.
Hotshot
Joined: Jan 2011
Posts: 13,120
Likes: 345
From: THIS IS SPARTA!, ...Mo.
You're doing great! My 300 six and four speed gets around 9 mpg. 300's are dirty running engines. They make gobs of low end torque, but fuel efficient they are not.
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Post Fiend
Joined: Mar 2011
Posts: 8,501
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From: Lynchburg, VA
The 300 is a heck of a lot better on fuel than the larger V8's. A "dirty running engine" is improperly tuned/maintained.
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Senior User
Joined: Mar 2007
Posts: 318
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Just wondering if you use the ferry or the bridge when you leave the island? I was on Whidbey Island around labor day. Was looking for your highboy but didnt see it. Just use whatever gallons it takes to fill the tank to figure out your mpg. Personally Id be happy with your mileage in a highboy even with a 300. Thats a lot of truck to move and keep moving. Plus everyone lies about what they actually get in fuel mileage ha ha
Lead Driver
Joined: Dec 2012
Posts: 7,870
Likes: 47
From: Tennessee
I think what the others are hitting on is the fact of the gauge not being accurate . Empty being the least accurate . So pick a half or quarter mark . Fill from there . Record the gallons . Next half or quarter ( Half may give better results ) fill and account for miles and gallons . Record over at least 4 fill ups to get an accurate record of MPG .
Hotshot
Joined: Jan 2011
Posts: 13,120
Likes: 345
From: THIS IS SPARTA!, ...Mo.
Well then Ford let A LOT of improperly tuned engines off the assembly line. I was doing emission tests on BRAND NEW fuel injected 300 six cylinders back in the late '80's and I had a problem getting the sixes to pass emissions with less than 5,000 miles on them.
Thread Starter
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Cargo Master
Joined: Oct 2010
Posts: 2,339
Likes: 32
From: Lost In a Pit of Despair
I think what the others are hitting on is the fact of the gauge not being accurate . Empty being the least accurate . So pick a half or quarter mark . Fill from there . Record the gallons . Next half or quarter ( Half may give better results ) fill and account for miles and gallons . Record over at least 4 fill ups to get an accurate record of MPG .
-Jameson
Last edited by jgavac; Oct 8, 2013 at 08:56 PM. Reason: added another quote
Post Fiend
Joined: Mar 2011
Posts: 8,501
Likes: 4
From: Lynchburg, VA
I'm referring to the older carb'd 300's, though what can you expect out of an early EFI, crude EFI system?