Just returned from a trip to Washington DC. It is 511 miles each way. Going up I set the cruise at 75 mph and got 20.1 MPG.
There was quite a bit of traffic going up.

On the return run, I set it at 74mph. Virtually no traffic, got 24 mpg.

All calculated manually. I fill till it clicks the pump off and don't try and top it up any further.

I know, I know, a million variables can be figured in. Bla, Bla, Bla!!!!

BUt, I am very happy with the results. I have gotten the same in the past. If I stay at 74 or less I get tremendous mileage. Go over 75 MPH it drops to 19 mpg. Go over 80 and it drops to 16 mpg.

Hmmm, lets see I just don't seem to be able to find anything about the 600 motor even coming close.

 

I can't remember who posted it, but it really made sense to me.

To check your mileage, keep a running total of total miles and total gallons of fuel. In other words, keep adding to those numbers everytime you fill up.

This way you will get a very true overall average of fuel mileage and you don't have to worry about how you fill the fuel tank.

 

I use the VRS System from Kjon Software. [kjon.com] everytime I get fuel I write the odometer reading on the back of the receipt and enter it when I get home. The software is free if you track three or less vehicles and tracks everything you could want.

 

my 600 only has 2300 miles on it now and the running avg is 19.9 mostly loaded can't complain about that its only gonna get better as the weather warms and the summer fuel comes in. The milage isn't bad on all of them and I suspect that the ones with poor milage on the 600's had poor milage on previous trucks too. It's all the way you drive Ido appx 75mph highway, 62 on state roads ,and the speed limit in town.

 

by the way its 4wd also you gain 3-4 mpg by being 2wd.

 

I am really glad to read this about your mileage. While I am sure that others are experiencing the same good results, yours is the first I have actually seen posted.

Seems every 600 I read about is getting horrid mileage.

Hope it keeps improving.

 

My son just called me and gave me a report on how he's doing with a fair load going up to Vancouver. The traffic through Seattle and Everett was the usual slow go. Then it opened up so he could cruise. He's got a 3500 SRW, 3.73 gears and he's got an 8.5 foot camper on, and he's towing a 27' car trailer. The truck weighed in just now on the scales at 10,900 and the trailer was 8,840 for a total of 19,740 lbs. He's getting 11.9 mi/gal at the first fill up. With a dirty air cleaner.... **** kid. He's got just under 20K on this truck and he pulls the trailer 3 times a week. It's deffinately broke in.

 

Spudman is definetly the minority with that kind of mileage...I would have to see the sticker that says 325hp before I believed it....especially being "loaded" half of the time. Sounds about like a 555 instead of a 600.

 

I didn't know the numbers went past 13 on the overhead, aleast I have never seen it. 2500 miles and lots of fuel later and still waiting.

 

You are free to see the engine sticker any time you want I still have the window sticker too if ya'll want to see it . Belive it it's a 600 and it's treating me very well. Based on a lot of the posts it's always the same people complaining I honestly don't think there is much of a problem and the 555 numbers I've seen posted on this sight don't look any more impressive, but whatever floats yor boat I guess

 

I have 1400 miles on my new 3500, 600 4.10 rear end and have seen a steady increase over the 5 or 6 days that I have had it. At first, I was getting under 11 reported on the overhead on the first tank running between 70-75 for the whole tank (bringing it home). The second tank it reported about 12.5. Yesterday, I hooked up to the 14,500 pound fiver and drug it around at about 50 for 200 or so miles. This really worked it out, as it had to work to maintain such a slow speed in 6th gear pulling grades. Well--******* it out a bit sure seemed to work as I was getting right around 16 running 65-70. I hope that it will continue to climb, but I myself would be happy with these numbers as I think it is an impressive feat. I love this truck.

 

Don't worry. Your mileage will continue to increase. Mine kept improving up to 20k miles but I only tow about 4k lbs once in a while.

 

Spudman, I truely hope our right. As is usually the case the people with a problem, be it mileage or anything else, are the ones we hear about most often.

I've seen more than one post from guys stating their 555 is giving horrid mileage as well. Just seems that there is an unusually large number of complaints about the 600.

 

Well i think the manufacturing date has alot to do with how well it does ! mine is getting around 15 mpg around town and has got 21mpg on a 280 mile trip running 70 mph.it was manufactured in Feb 2004.and it is 4x4

 

I agree! My motor was also manufactured in February and I am getting around 20 mpg highway with my 600.