Fuel economy & 727 w/ 3.07's

[btoscano]

Running flat out I get 18. 5 MPG in my '90 D250 w/ a 727 & 3. 07's. Speed limits here are 70, so with foot to the floor on flat/slight hills the speedo will read 78. Up the steepest interstate grade in the state the truck will do 72.



I am wondering if this is about right and if I put in new injectors or advance the timing I can get a little better fuel economy?



I checked the valves over the weekend, 3-4 seemed slightly looser than the others, and as best I can tell the valves had never been adjusted before. I only adjusted the 3-4 but I think I can make them all a hair tighter. I'm not sure I understood the difference between "some" and "very slight" resistance of the feeler. All my other cars have had hydraulic lifters!!



Thanks,

Brian

 

[phillips5]

Back in december of 88 my brother and I bought a pair of dodge cummins His 727 307 got 26 mph going to chicogo on the turnpike. with no mods. You can up grade inj and other mods. but when you catch the fever you won't keep your foot out of it and suck up any milage you gain.

 

[Forrest Nearing]

man, get a GSK like YESTERDAY! I couldn't imagine not being able to do 80mph!



Forrest

 

[dpuckett]

Forrest, I think he'd do better with an OD than with more RPMs. Takes fuel to make RPMs. ANd, WE can get a "GSK" for $15.



18-20 sounds about right for the age and miles and gears. Remember, sometimes it IS the years, not the miles. The guy who got 26 with a stock 89 was also running better fuel (MPG wise) than we have now, too.



Daniel

 

[btoscano]

Daniel,



I'm not sure the fuel quality matters much on these "slow turning" diesels. Have you noticed a difference between stations? On my MB diesels which I have a lot more experience fuel can make a 20% difference in economy.



What else about the "age" might be the cause? Would new injectors improve economy? Advancing the pump to account for timing gear wear?



My 727 trans is making metal, brass in the pan. So its going to get replaced. However, this is a "work truck" and I don't want it to turn into a money pit. No one has come knocking on my door with a 518 and a driveshaft. Now if it were a 4x4...



Thanks,

 

[Forrest Nearing]

well, more RPM is a lot cheaper than an OD... the difference will buy a lot of fuel



I seem to remember seeing a 518 on ebay recently for not too much money.



Forrest

 

[phillips5]

If the timing has never been advanced than yes it will help

 

[1stgen4evr]

Watching this post

I have the 727 - 3:07 in my 89. I haven't driven it much and can't comment as to mileage but even with the 3:07 the rpms are too high for my likeing. I just don't want to run wide open to go interstate speed. That is the reason I plan to go with an OD in that truck. Work truck around town etc, it would be fine just like it is. In fact that is what we are doing with it now. The wife uses it for yard chores, miscelaneous light hauling. If you are going for mileage, get a manual transmission.



What is a GSK. Not familiar to me.



James

 

[btoscano]

I think the GSK is governor spring kit to bump up the RPM's that the pump will turn the motor.



I was just wanting to make sure the truck is in line with what others are getting. Not trying to set any records with a non-OD transmission. The Cummins motor can take running with the foot to the floor all day long from what I understand. The truck isn't worth adding OD to me at this time.



-brian

 

[cerberusiam]

GSK for a VE = +3200 RPM govenor spring.



That configuration should have done 85 to 87 mph on the flat when new so you have either lost fuel or power transfer. Probably a little of both. Thes motors will run at 2900 rpm's constantly but the fuel consumption is not the greatest so slowing them down will help the mileage. You are probably getting good mileage considering what you have described.



You can keep the 727 and rebuild it but toss the stock converter and get a tighter one. That will make a difference in your rpm's and top end speed. If you need some more crank up the high idle and the fuel screw. At that point your right foot is going to be the controlling factor for mileage.

 

[1stgen4evr]

Pedal to the metal

The Cummins doesn't much care whether it is wide open. I just don't like the high rpm. It wears on me after about a day on the road.



Ditto on toss the stock converter. There have been lots of improvments since 89.



Remember that the timing is already higher on the 89 than the later intercooler models. PM Jleonard on that as to the best setting.



There is a difference in twd and fwd. Mine is a twd. The innards are the same.



I don't know what is in the torque converter as far as thrust washers. I have only cut a couple open. One was from a turbo hydromatic. It had thin roller thrusts washers. Something gives out in there. My 92 with OD is getting so slushy that it will hadrly pull off with a load. And it is shedding bronze as well as aluminum.



James

 

[ctd8999]

Check your throttle linkage the cable tends to strech and you will not have full throttle

 

[Philip]

Your MPH seems low at WOT. I have 3:07's in my rig. I can hit 89 MPH in 3rd before the engine defuels.



Check the throttle linkage like ctd89 suggested.



In OD I get 20 MPG with training wheels on. You should be a little higher being a D250 compared to my W350 dually.

 

[btoscano]

I'm glad I asked this question.



I will check the throttle linkage.



I'm going to have to pull the trans so I can replace the TC when I do this. Any suggestions on what and where I should buy one? I guess something that's more modern, that will work well in hills/mountains and not give up too much trailering ability. I don't trailer much but if I do, it will probably be a full size car trailer and it will probably have to climb hills/mountains on "backwoods" roads and mountains.



Thanks,

 

[pepecat]

MPG's 727 & 3.07's

I'm a new cummins owner of an '89 d250 bone stock 2X4 with 727 and 3. 07's and so far my MPG's have been around 18. 5-20 going about 70 MPH average HWY. If I press the throttle down to the floor it will go 73-75, and if I put more pressure on the pedal after that, I will get up to 85 MPH. I think I need to either tighten my throttle linkage or just leave it be. If I had the patience I'd drive 55 all day just to see what MPG I would get. I've considered getting gearvendors OD but you know what It may be best to just leave it the way it is and sell it and put the money I would've spent towards (the down payment of) a cummins 600 or 98. 0 manual 4X4. Check my read's rigs to see my truck. Currently it is down for the count because the right axle seal is leaking bad. Just had the left replaced. I have to check that axle vent. I wish I knew what it looked like, or where it was...



Have a good one, also you're lucky that a 727 rebuild is dirt cheap

 

[1stgen4evr]

axle vent

On top of the drivers side axle tube where the brake line makes a zigzag. About half way between the spring and centersection Rubber line that goes up and loops back over the cross member that the shock upper end is fastened to. Vent is on the end of that hose. Entire hose may have been ripped off. There shoud be at least a nipple on the tube where the hose was.



1stgen4evr

James