My dad has given me his old 1989 F250 with a 5.8L EFI automatic trans. excellent truck with 300,000 and running strong but a little too thirsty for my wallet. I want to swap to a more economical engine without too much hassle although I am not adverse to changing the transmission or doing major electrical work if needed. The truck is used as my daily driver and I haul mostly light home building equipment. Thanks.

 

What transmission, axle gearing, and tire size? Check the calibration decal on the drivers door pillar.

How are you calculating milage and what is it getting now?

Are there any codes present?

 

You've got a big truck with a big motor. With a good tune up and everything running in good shape you should be able to manage 12-14 MPG with that set-up. If thats not good enough for you then I'd look into getting a different truck personally.

 

Swap in a 4bt cummins or a 4sumthinorother Isuzu motor into it.

Cost is the issue with any motor swap. Meaning how much to put it in there and then how much to operate.
It would take you many many years to make up the cost of a motor swap to a diesel.
Like was said before. Tune up and light foot. But don't expect more then 14 with a 351. I'd rather have the 460 because the saying is... 351, power of a 302, mileage of a 460.

 

If the basics for mileage are there, overdrive transmission, 3.55 gears, stock tires, you can do pretty good considering what the vehicle. The f350 in my signature, even loaded with tools at about 7800 pounds still gets 16-17mpg between palm springs and vegas. But I've got overdrive, 3.55's and stock tires.

 

A lot of your issue could be the way you drive. I have no idea how you drive but that could be a reason. My buddy has an 06 taurus that he gets 22 MPG day in and day out. I get in and drive it anywhere, town, highway, ect and I get 32 MPG. But then again, it's his car so I don't beat on it and I drive really conservatively. When I drive my truck with a 351w I get 7-9 MPG but then again, I don't have OD and I drive it like it's mine.

 

Thanks for the follow up. To answer some of the questions raised, the truck has a E40D transmission with a code 39 axle, (Axle Code 39 is a non-limited slip 3.55 axle I think) stock tires that I try to keep properly inflated and I still get 8 miles to the gallon calculated on a running average of miles used and gasoline put in the tank over at least a couple of months. It sounds like I should be averaging at least 12 miles per gallon if I am driving conservatively. I think my first order of business is to make sure that the car is well tuned. As far as to when it makes sense to change engines, well I figure that right now I drive about 15,000 miles a year and get 8 miles to the gallon at $4.50 a gallon here in San Diego that's $8,437.50 per year and if I improve mileage to let say 14miles/gallon that would be $4,821.39 or a saving of $3,616.11. Well that sure looks like I can recoup an engine transplant pretty quickly if I am unable to improve mileage otherwise, so the question becomes what would be a reasonable engine swap for this truck because if I invest $3,616.50 and get more than one year use I would save some real dough.

 

Yeah, your truck is probably just in need of a serious tune up; I can still get 14 average with 4.10 gears. If you're really serious about a motor swap you could always go with a newer 5.8 to keep things simple and keep costs down. If you want to go diesel like UNTAMND suggested, the 4TB is a good option. Tons of guys run them and you could get really good mileage with them. I'm not sure of the exact specs but power will be similar to what the 5.8 puts out but the Cummins will have a lot more torque.

 

ever think about a 4.9? they were used in all types of applications, even dump trucks and UPS trucks. I get about 18mpg with mine (it's 4x4 too) with 3.08 gears and 30" tires. Look around, you can usually pick up an engine fairly cheap, as they tend to last longer than the truck itself

 

An engine swap is not the answer here IMO, all of the available engines produce about the same milage in any given vehicle(a 4.9 will NOT get 18mpg in an F250) so you don't stand to gain anything for all the work involved. The engine you have is capable of double the milage it's getting now so I suggest you simply fix what is wrong with the truck.

8mpg is terrible but not uncommon unfortunately and indicates you have one of several issues with your truck that are relatively inexpensive to fix. The problem with the biggest potential impact on fuel milage is fuel transfer between tanks, if your truck has dual tanks does it get the same mpg on both? It should so if it doesn't that indicates fuel is being pushed into the other tank as you drive and out onto the ground if that tank was full to begin with and that will waste a lot of gas obviously. The fix is to change the fuel delivery modules in one or both tanks.
The other issue is related to sensors, any major sensor issue will put the computer in openloop all the time and that will double fuel consumption, so you really need to check codes and fix any problems that are flagged.

 

I can see 8 mpg real easy if it is alll stop and go city driving, or it is during the winter when running the oxygenated fuel.....

I run 8 with my 460, 10 with my 351w and ran 12 or so with a 302. All are/were EFI and all were in Ford trucks and city / trafffic driving.

Sitting at lights every block, for as hour (or two or three) on the freeway at 1-3 mph, takes it toll on mileage. Colder weather during the winter / longer warm ups also takes more fuel. Now is not the time of the year for mileage checks, at least where I live!

Open hiway, no traffic, steady state driving, or WITH summer fuel, mileage comes way up.

David

 

Do a full tune up:
distributor cap, button, wires, plugs, fuel filter, some injector cleaner/lube, air filter, and couldn't hurt to advance the timing.

 

I do mainly city driving in my truck and average ~9 mpg. If I hop on the freeways it goes up to ~13-14mpg. But like mentioned before, I don't drive it crazy. With a good tune up your truck should get better mileage.

 

I only get 10mpg with my 300 and those are the larger imperial gallons, I drive with a light foot and its downhill all the way to work...,I was just browsing here to see what the 302's are getting

 

My 89 F250 with 302/aod 3.55 gears/stock tires. I get 13 to 14 MPG and its mostly highway speeds.