surprising mileage.

[mexicanjoe]

I was talking to mechanic buddy of mine , complaining of the crappy mileage in town. I explained that I got maybe 12 mpg..... He asked me what rpm I shifted gears, I replied about "2,000 rpms".. He said: that big 7.3 wont have any problem pulling you around, try shifting it at about 1,200 rpms". I thought the man was crazy. "I have a 4.10 rear-end in the thing ,brother" I replied. He told me to try it........So here goes; I managed 19 on the highway and 17 in town... i know it sounds crazy but it works. I don't lug the engine and I dont drive much over 45 mph around out in the county, but this is amazing.

My engine had also been running rough until the GP gave out.... had to use a little ether every morning. Well, butter my butt and call me biscuit::: I think that little ether every morning may have knocked some carbon loose, cuz here we are idling smoothly at stop signs..... coincidence???? dont know, but one happy driver.
Give me your thoughts.

 

[Farmer Rock]

Hey there biscuit
To me,just putting around town (empty of course) and shifting at lower rpm is fine, but i think 1200 is a little on the low side once you get above second gear. Obviously once you get in higher gears you have to run higher rpm, so it kind of seems like you would only be saving such a small amount. The big problem I see with people just idling along like that, is if your just making short trips all the time, it probably won't be running hot enough to prevent wet stacking.



Rock

 

[chris142]

Mine will pull@1200 but it sure does smoke too.

 

[Jonathan Graham]

Mine will pull@1200 but it sure does smoke too.

Mine smokes like crazy if I'm under load at such a low RPM. I've always thought it was part of the deal with the IDI's.

 

[catbird7]

I've noticed similar poor mileage while drive slow on dirt roads. Almost seems like you burn the same amount of fuel in one hour driving on dirt at 20mph or one hour driving 65 mph on the highway. Obviously it's not that bad, however these idi's certainly seem proportionally different than a gas engine under the same conditions.

 

[mexicanjoe]

we'll find out this week when I have top make a 104 mile round trip tour of the flat west Texas countryside. Im sure the mileage will be less. Im looking to change out my valve cover gaskets, they sure are weeping oil everywhere.

 

[Sergey]

I was talking to mechanic buddy of mine , complaining of the crappy mileage in town. I explained that I got maybe 12 mpg..... He asked me what rpm I shifted gears, I replied about "2,000 rpms".. He said: that big 7.3 wont have any problem pulling you around, try shifting it at about 1,200 rpms". I thought the man was crazy. "I have a 4.10 rear-end in the thing ,brother" I replied. He told me to try it........So here goes; I managed 19 on the highway and 17 in town... i know it sounds crazy but it works.

Really ? Days back I experimented how to get the fuel mileage on my 85 with 6.9 and T18.
Never got above 16 mpg despite what I tried and about 12 in city. Yes tried shift up at 1200, also at 1500 rpm. It shifts and accelerates slowly, but mpg was still low. Then years passed I gave up to worry about fuel mileage on the truck since both of us got old and don't spend much time together these days.
Perhaps your truck is in such a good shape to get such high figures?

 

[frankenwrench]

Really ? Days back I experimented how to get the fuel mileage on my 85 with 6.9 and T18.
Never got above 16 mpg despite what I tried and about 12 in city. Yes tried shift up at 1200, also at 1500 rpm. It shifts and accelerates slowly, but mpg was still low. Then years passed I gave up to worry about fuel mileage on the truck since both of us got old and don't spend much time together these days.
Perhaps your truck is in such a good shape to get such high figures?

Timing helps alot, and so does overdrive. Which your t19 doesn't have. Best I got with a t19 was 17 mpg. Mainly due to flat ground here in tx and 3.55 gearing and easy on the throttle. I still shift at 2k rpm unloaded

 

[Sergey]

Timing helps alot, and so does overdrive. Which your t19 doesn't have.

Ah, so yours is 5-speed, then why not 19 mpg hwy. The best habit I used with T18 is to aggressively use neutral gear to just let the truck roll where possible.

As for timing my truck never had one checked or adjusted, not sure if it is worth to put any money into a worn 35-year old motor. It probably could benefit from timing adjustment to some degree.

 

[frankenwrench]

Ah, so yours is 5-speed, then why not 19 mpg hwy. The best habit I used with T18 is to aggressively use neutral gear to just let the truck roll where possible.

As for timing my truck never had one checked or adjusted, not sure if it is worth to put any money into a worn 35-year old motor. It probably could benefit from timing adjustment to some degree.

Definitely worth having timed in my opinion. I have alot of CDD upgrades as well as a 5 speed on my 91 7.3 and 3.73s and 19 mpgs is easy to come by even when I'm in a "hurry". The 85 6.9 with t 19 I just haven't been able to quite get that. Neutral rolling is a must in that 85 I have to get the 17 I do get with that one as it doesn't have overdrive. Now the 5 speed with the upgraded pump, injectors, intercooler, and turbo with the 3.73 gear in the back doesn't get to roll much in neutral as I usually have alot of weight on the trailer that rarely gets disconnected from that truck

 

[IDIBRONCO]

Years ago I had a guy swear that his 86 F250 4x2 with a 6.9 and C6 got two MPG better after I set the timing for him. I don't know if it was true, but that's all I have.