bad mpg
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New User
Joined: Nov 2010
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From: cleburne tx
bad mpg
hello i am new here and was hoping you all might point me in the right direction i have a 1984 f250 with a 4.9 engine t-18 transmission and 373 rear gears stock engine reman mid 70's carb and duraspark 2 same vintage
this truck i have owned for about 6 months and it gets about 10 mpg average it is a daily driver rarely pull anything with it kinda over kill for a cruiser truck
i am wondering what i can do cheaply for couple hundred dollars to increase fuel mileage i drive slow old women pass me i drive about 55 engine runs 2500 rpm on aftermarket gauge
should i put a higher gear rearend in it to lower rpm or maybe a aod auto i am sure if i can drop my rpms it will get better mileage any other ideals my t-18 is very very sloppy so changing it is something that might need done anyway
can you all point me in the right direction
this truck i have owned for about 6 months and it gets about 10 mpg average it is a daily driver rarely pull anything with it kinda over kill for a cruiser truck
i am wondering what i can do cheaply for couple hundred dollars to increase fuel mileage i drive slow old women pass me i drive about 55 engine runs 2500 rpm on aftermarket gauge
should i put a higher gear rearend in it to lower rpm or maybe a aod auto i am sure if i can drop my rpms it will get better mileage any other ideals my t-18 is very very sloppy so changing it is something that might need done anyway
can you all point me in the right direction
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New User
Joined: Nov 2010
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From: cleburne tx
the timing is set by a vac gauge and has a 6 month old tune up and at the same time i replaced the tfi crud with new reman ignition box and coil and disturbutor new plugs and wires at the same time also replace the junky carb with a reman for a 78 ford 3/4 all parts where ordered for a 78 3/4 ton truck fires up every time but goes though both tanks in about 256 miles thats 8 days of driving for me
Lead Driver
Joined: Jul 2009
Posts: 6,477
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From: Sheffield, AL
Welcome to the forum, 4.9ford1984!
A tune up has already been discussed, so here are some often over looked minor details:
low tire air pressure, dirty air filter, dragging brakes, alignment problems, incorrect thermostat, clogged catalytic converter, unnecessary weight or extra aerodynamic drag [i.e. spare tire on roof, extra light bars, etc].
Just some random thoughts.
A tune up has already been discussed, so here are some often over looked minor details:
low tire air pressure, dirty air filter, dragging brakes, alignment problems, incorrect thermostat, clogged catalytic converter, unnecessary weight or extra aerodynamic drag [i.e. spare tire on roof, extra light bars, etc].
Just some random thoughts.
Senior User
Joined: Sep 2010
Posts: 115
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From: Northeast Oklahoma
All these things will help, however, I wouldnt ever expect anything better than mid to low teens, if you could even break into the teens at all, out of a 3/4 ton gas truck no matter what engine, tranny and rear end its running. 3/4 ton trucks will always get lower mileage simply for the heavier frame, suspension and parts that are on the truck. The only way I have ever successfully gotten decent mileage from a 3/4 ton truck and I have ran them for years was having a diesel in it. The old 6.9 and 7.3 IDI's would get pretty decent mileage out of a heavier truck and you can put mods on them to put out pretty impressive horsepower and torque #'s for towing.
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Joined: Nov 2010
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From: cleburne tx
ya i know it will cheaper to just to buy a half ton. I only bought the 3/4 ton because it was cheap and not very much rust just hate to buy a half ton and deal with someone elses failed project and the gremlins they have hid for now i will suffer with the bad mpg
Post Fiend
Joined: Jul 2004
Posts: 8,786
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From: Northern California
The 3.73 gears is whats causing most of the poor mileage in my opinion. I wouldn't have a 300 with over 3.25 myself. A 302, sure but not a 300.
If you could get that truck to be in the RPM range of 1800 RPM at 55 mph, that will help your mileage greatly. It won't be able to do the amount of work it used to though, so it will be a trade off.
If you are just going to use it around town, on flat roads, try around 3.00 gearing. If going to use it for working or some up and down hills etc... 3.25 would be good choice.
Since it's a F-250 I would not recommend going higher than 3.00 example the 2.75 gears are ok for a F-150 etc..
Hope this helps.
If you could get that truck to be in the RPM range of 1800 RPM at 55 mph, that will help your mileage greatly. It won't be able to do the amount of work it used to though, so it will be a trade off.
If you are just going to use it around town, on flat roads, try around 3.00 gearing. If going to use it for working or some up and down hills etc... 3.25 would be good choice.
Since it's a F-250 I would not recommend going higher than 3.00 example the 2.75 gears are ok for a F-150 etc..
Hope this helps.
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Junior User
Joined: Jul 2010
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Yeah i have a 351 1/2 ton and am lucky to get 11 or 12. But I am in a busy city driving area so that kind of sucks it dry...
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