My F-100 gets 9.5-12.5 mpg with a 360. Thats about the same mpg I got in the early 80s with a '73 F-100 360 C6 and real close to what the two '79s I had with 351ms got.

I bought a new '89 F-250 with the idi 7.3 in it and came to the same conclusion that several here stated: considering what the diesel option costs, plus the added expense; As Josh said, 10qts oil (changed mine every 3k), two sets of expensive batterys for it at least once, maybe twice in the 4 years I owned it, the fuel filters were expensive etc etc. I was farming at the time and burning tractor fuel @ anywhere between a low of 45 cents and $1.20 depending on the time of year, if not for that it would not make sense economically. I believe most folks who have diesels dont need them and would be better off with a gas burner. Now if you tow, its a different ball game.

 

Oh I definitely tow with mine...we pull our 26' sea ray cabin cruiser boat(ocean boat) with it,and I've also once pulled 10 tons of hay out of Klamath falls Oregon back down to Fresno with it...truck pulled it 65 the whole way and got the same fuel mileage as if it was empty. I wouldnt get rid of my Cummins unless you brought me a nicer one lol

 

You were asking about the mileage of a 390. I have an all stock 390 in my '76 F-150 and right now, I would probably be lucky to get 8-10 mpg. I bought it from my Father-in-laws estate when he passed away several years ago and at the time it was running pretty well. It only has about 80,000 original miles and I think that I got about 15 mpg when I first got it on a trip up into northern Washington state with steady driving about 60 miles per hour. I wouldn't count on getting that much though.

I have considered getting an O/D transmission and several years ago, I found a link to a company in Canada that made an O/D that would bolt up to an FE block and if I remember correctly, it cost about $2,500 to $3,000. I don't know if they are still making them though.

I do have one question that maybe someone on the list could answer. I currently need to rebuild the 390 and I understand that they are fairly expensive to rebuild and I was wondering if someone has recently rebuilt one and approximately what the rebuild cost?

Also, when I do rebuild it, I am thinking of putting in a mild cam for towing to increase the power a little. Any thoughts would be appreciated.

At the present price of gas, I can't afford to drive it much, but it is my back up truck and if I need to pull a heavy load, it does serve well.

Thanks for any inputs. norseman

 

Best I have ever gotten with one of my trucks with an FE is . 15 mpg on highway. No towing, or load. Its a 428 and toploader 4 speed. Driving around my house and short trips to store etc its gets 12-13. It has never been 10 or lower, not even close to that poor.

 

I've got a 390 in my 67 Galaxie convertible. The last road trip I took it on I got right at 20 mpg. Yes, I was driving like Uncle Fudd and didn't exceed 62 mph. I was expecting half that and would have been thrilled with 15 mpg.

 

There is a huge difference when driving older carburetted ,especially, vehicles at speeds on the highway. Seems as a general rule, when you hit from 60-65 mph the fuel economy drops dramatically. Newer vehicles, not so much.

 

What this basically comes down to is that you will spend a grand or so upgrading from ~10mgp to ~12 mpg. I'm basing all of this off of $3 per gallon. If you drive 5000 miles a year you will spend $1500 with 10mpgs and $1250 with 12mpgs. If you spend a grand upgrading your vehicle you will break ever at 4 years. That will bring your total after 4 years with both 10mgps and 12mpgs to $6000. After 4 years you will be making money. I don't really see it worth it. But just my 2 cents.

 

Mud, depending on how you look at it, yes you can be correct. If someone buys a new vehicle just for a mileage increase, its gonna take a long long time to get it back.

 

Yea that is how I see it. You will spend money trying to save money.

 

But I believe a lot of vehicles bought are for more than just a mileage increase. So it is makes you happy and you get better mileage in your mind its worth it. If you like what you have and only want better mileage, there are things you can do much cheaper than buying a new vehicle

 

Yea true. I guess as long as your happy yourself I guess it doesn't really matter.

 

I notice a huge difference in MPG in both my 06 Superduty and 04 Maxima. After 65 mph in the truck and the mileage tapers off. After 72 mph in the car the MPG nosedive from over 30+(65-72) to just over 24 mpg.

Josh

 

The cost to rebuild a stock FE to stock or near stock specs isn't that much more than any other V8 in these trucks. The cost difference increases significantly (akin to the 351M/400) when undertaking a high performance build due to the relatively low production and the popularity of the vehicles in which they were offered. Compare that with the 302W, 351W, and 460 who have strong aftermarket support due to the length of time in production.

 

75 Highboy with mild (fresh) build on '66 FE390GT motor (9:1 hypereutectics, old Holley single plane & Carter 650), C6, 203 T/C, 4:10's, 35 TA's.... I get a respectable 10-11 in town and 12-14 highway with light foot on the skinny pedal. Towing a 20' ski boat doesn't change much unless pulling a big grade. My son's 2004 F150 SCSB 5.4 with 35's gets worse fuel economy than my Old Brown.

 

here is a link to Survival Motorsports Home Page survival motorsports they are in to performance rebuilds for fe motors. i have a 390 in my 68 torino that is about 400hp on pump gas if it gets 6mpgs i would be impressed.