Hi All,

My first post on the board. here is the deal,I just got back from Texas on my first LD trip in the truck(92 f-250hd 4x4 LB 7.3l idi auto 283k) going out to texas weather was pretty mild and I am a 60 by 2 kinda guy, wife was ok with this due to the rain most of the way. I managed to get 24mpg out of the old truck. so I am pretty pleased because around Atlanta I get 16-17mpg. so I am about on target with what I think the truck should get.

Now comes the problem, it is hotter on the way back( no rain to bail me out). the wife like most women has no internal temp controls ,a bad termostat and a even worst warranty. but I digress, so I turn on the a/c and we run it on the front tank. I look down at the fuel guage and notice I am about out and the trip shows about 187 miles traveled. I'm thinking great the fuel guage is going, but it is not, the tank is really almost empty, so I fill up and did the math and only got 10mpg. Now I know what you are thinking, maybe I driving faster going out than in. the cruise was on both ways and set to 65mph.

So my question is, is the a/c compressor on the diesel engine so much of a bear to turn that a truck designed to tow over 10k pounds behind it is getting it butt whipped by it. even when I towed that much, my milage was never that bad. so I need a little insight from you guys that have owned a diesel for awhile. what kind of milage are you guys getting running the a/c? I cannot confirm this, however I do belive the truck has been converted to r-134 from r-12, would that make a differance? the last Deisel I drove was a 88 IH 3.5 ton flat bed with no A/C(thank you USMC). so I don't really have a idea if this is a problem of not. thanks for any help you guys can provide.

V/R
John

 

something else is at work here. You aren't losing that much mileage from normal function of the AC.

 

cool moist air = high fuel mileage
hot dry air = low fuel mileage

 

saengjwi,
Welcome to FTE and the IDI diesel forum.

Many factors are probably at work on your mileage.
tjc transport just named two biggest factors most likely.

Also wind will affect the MPG more than you might think, a 4x4 has a rather large frontal area and the big hole in the back don't help either. Did you have a tail wind on the way out and a head wind on the way back?

Were your speeds about the same?
You may have been driving a bit slower or more smoothly in the rain than you were on dry road.

In a car, which is a bit more aerodynamic than your truck, running the AC with the windows rolled up will increase you MPG over what it would get with no AC and the windows down.

Our trucks are not aerodynamic, so running the AC will drop the MPG, but not that much.

 

Last year my father took my '90 7.3 from Phx. AZ to Dallas up to Oklahoma than back to Phoenix, the Diesel from different stations changed the mileage up to 8 mpg on that trip. I have always kept a fuel log and can tell which stations get the best mileage.

 

Hey thanks guys for the input. I think it was a combination of the things that were pointed out. When I fueled-up in La. the truck seemed sluggish. I will keep the fuel quality in mind next time. the roads were craptastic in La & MS, the truck was bounceing all through those states. I will start a fuel log too, thanks for all the help.


V/R
John

 

I haven't noticed a real difference with the AC on in my truck in regard to fuel economy.