I was wondering what some real world numbers on the effects of towing a car are instead of estimation calculators. I have a 1966 F100 that has a 351 Cleveland (previous owner's idea) the stock specs for the motor are 250 Hp @ 4600 rpm (I never take past 3200 rpm) and 355 ft.lbs torque @ 2600 rpm, it has a bit of a cam in it know with an Edelbrock performer intake , 500 cfm carb Petronix distributor, stock exhaust and the transmission is a M5OD-R2 from an F150. Currently it gets 11-12 mpg on the highway @ 60 mph. I will be towing a 1970 Fiat 124 Spider (2000 lbs) on a uhaul trailer (2200) some 600 miles. I need to tentatively plan my fuel spots. So could I expect 7 mpg if I keep my speed @ 55 mph? The majority of the trip is through Oklahoma so it is pretty flat. So if anyone could help me with how much of a mpg hit I will take towing the car it would be greatly appreciated. Thanks.

 

I don't think your drop off will be that bad. I have a diesel Excursion and normally get about 16 to 17 solo, I got 14 pulling a jeep patriot on a uhaul flatbed from Indy to Columbus Ohio with my cruise set at 70.

I would think you will get between 8 and 8.5 mpg. Just my opinion.

 

I would say that 7-8 sounds about right on that old carbureted engine, I would watch the temp gauge as well. It may help to keep a 5 gallon can or 2 in the bed of your truck. The truck should handle it ok but that was a truck designed when speed limits were 55 mph so I wouldn't push it much past that.

 

Based on 11-12MPG empty I'll guess 9MPG with a Uhaul trailer and Fiat, with no wind. If you have a headwind it will be worse. If you have a tailwind it will do better.

Let us know how it came out. I'm sure we're all a bit curious.

 

Thanks for the replies. I will be be taking 10 gallons of extra fuel just in case I can not make the 95 mile stretch between Buffalo OK and Hooker OK. I will update when I make it.

 

How big is/are the fuel tank(s)?

 

I want to say the in cab fuel tank is 16 gallons in my 71 F100, maybe his '66 is similar sized

 

Well, my 9MPG times your 16 gallons is 144 miles of range. Hopefully his truck has two tanks.

 

I think my tank is 18 gallons, I have my fuel stops set around 75 to 100 miles with the extra 10 gallons I think I will be fine. But this summer I plan on replacing the 351 Cleveland with a 300 I6 and rigging up a dual tank system. Again thanks for the feedback, I take off on Sunday.

 

Cool, let us know how it comes out!

 

In 1966 the speed limits were 70 mph on most highways. We didn't get 55 mph till mid 70's.
TJ

 

Well, I made it. I have been in New Mexico I haven't replied because I haven't had had internet. The trip went well and the truck did great I got 9.5 mpg towing, not bad. It seems my baseline mpg was a bit off due to the fact my new tires were not inflated properly, my bad I should have checked, and only had 26lbs of air in them after inflating them to 35lbs the truck got 13.8 mpg on the highway.All in all a good trip.

 

I'm assuming you were there at that time and I'll take your word for it, I'm a 1980 kid!

 

TJ is correct. 1980..........my kids were in high school then.

 

Thank you for posting that as I had to go back and check what year truck he had and said the same thing to my self, 60's child LOL

Good to hear you made it.
What I think some did not read is you have an over drive stick transmission with the 351 but we don't know what rear gear you have in that 66 truck of yours.
We also do not know was RPM the motor is turning at what speed?

If the motor is making it's power in the 3000 RPM range and you are only spinning the motor at 2000 or lower RPM range because of the rear gear and OD the motor may be lugging and not getting good MPG.
Also don't think going to a 300 six is going to get you better MPG either over the 351. You could be working that 300 a lot more (more throttle for the same speed) than that 351 motor (less throttle for the same speed).
Now the 300 is a low RPM motor and will pull from about 1000 RPM to a max of 3000 RPM and am told the best MPG is around 1500 to 1800 RPM.

My 81 F100 flare side with 300 six / T18 & 2.75 rear gear spins about 2300 @ 65 MPH and gets around 14 MPG. If I go faster the MPG drop a bunch and the speed limit here is 70 MPH but they all do 75+ more to the plus side LOL. I plan to add an OD unit at some point to lower the RPM and hope to get a little more MPG but it should drop the RPM into the sweet spot and not spin the motor to its upper RPM limit.
Just something to think about.
Dave ----

ps this truck is a back up to my 02 Durango (360/auto OD/3.92 gear) to pull my car trailer that I don't pull all the time now days like I did 5 years ago.