What happened to my mileage?

[4bogginchevys]

I too am hesitant to add another post to this long list, but to try and help I would guess that it's definately a fuel LEAK, my 1008 leaks some from the return lines every now and again and I dont always catch it right away. I bet one of the returns are leaking and like mine it just evap's on the ex. manifold while driving....or the last line on either side that most poeple put a screw in is letting fuel pour when under pressure. Good luck

 

[ragedracer]

Well, I finally got to drive it a bit and check for a fuel leak. None to be found. Pulled the air cleaner off and looked in the valley under the intake manifold. Dry as a bone. No wet spots on any of the fuel line connections at the IP. Dry around all the injectors. All the fuel lines are dry.

Dang.

Now I'm not sure what the problem is. What else could cause a steady drop in fuel mileage?

 

[kipman]

All the parts you need to rebuild your injectors, 62.00 with free shipping ebay number 150382440641

 

[jdemaris]

Now I'm not sure what the problem is. What else could cause a steady drop in fuel mileage?

Timing advance getting sluggish? The ignition timing advance is usually the first thing to wear on the Stanadyne DB2 pumps. Not easy to check on a 6.2 since the pump is buried in the middle of the engine. It CAN be checked with a gas-engine timing light if you have the proper adapters. Also can be checked with an expensive luminosity probe.

As a general rule of thumb, if the timing isn't advancing like it should - the engine will run ratty when you rev it up cold, no load. When you start it cold, and rev it up high while in neutral - is it smooth or does it skip a bit?

If the advance has gotten sluggish, there are some easy work-arounds.

As far as the high prices I've seen mentioned for pump "rebuilds. " Keep in mind that these pumps rarely get truely "rebuilt." They get patched up, recalibrated, resealed, and most parts used as-is with NO renewal process. So, the idea of spending big-bucks on such a pump seems like a waste to me. And, there's not much to go wrong inside a pump to give the symptoms you've decribed. All it is . . . is a low pressure hydruaulic pump coupled to a high pressure hydraulic pump with a governor, fuel metering valve, and distributor section added. The bulk of the pump is the distributor section - and when it wears, the engine won't start hot. Otherwise, it will usually work fine even if worn.

Sluggish timing advance, driving at high altitudes, plugged air intake, high rolling resistance. winter-grade "thin fuel" - etc. are some normal causes.
And, if the injectors are REAL bad, they can also do it. But, usually when they ARE that bad, the engine knocks something awful when you first start it.

 

[ragedracer]

Since I can't find any obvious fuel leaks and I'm experiencing none of the symptoms above, I guess I'm going to have to temporarily attribute it to "winter blend" diesel. I'll keep monitoring the mileage and see what happens when the blend changes back.

Thanks guys for all your time!

 

[Grantshire]

Yes...it could be the IP wearing out....but is most likely fuel quality. Blending of diesel fuels is probably the culprit. When they mix ethanol to fuels....sometimes it makes it way into diesel also....it doesn't burn good with high compression engines.

Just as a experiment......grab a couple of quarts of motoroil that you don't know the weight of.....put 3 or 4 quarts in your tank. You should immediately see a difference!

I've talked recently to reps for Kenworth and for Cummins both, and with the new diesel fuels that suppossed to be cleaner burning....they're 'dryer' than the old fuel.

Cummins has a system that takes a small amount of crankcase oil and adds it to the mix going to the engine to raise MPG's and to add some lubricity to the fuel.......

Uncle Sam has been doing WMO in Diesels for quite a while......since fuel quality is going down....it helps to use WMO in these trucks.....

Diesels were originally designed to run off canola and peanut oil at the processing plants....(free fuel).....it wasn't until the oil companys got a wiff that these folks were running their engines off waste oils and fluids that the oil co's can out with bonafid 'Diesel fuel'.....

In the engine manuals....your allowed to run about a 5 to 10% wmo on many engines.....These trucks we drive like the stuff.....

Been watching this thread with interest as my daughter's Oh-9 with 33" tires mileage has been bouncing around a bit, too. I have tried going back to 31" x 10.50 tires as suggested here but did not see much difference. In her case 55 of the daily 65 miles is Interstate driving at 65 mph. The 33" tires at 65 mph (probably closer to 68 mph) appear to yield slightly better mpg than the 31" tires but it is close.

I have been adding a bottle of 2 cycle oil to each tank but it sounds like that may not be enough. Can you explain the suggestion to add 3-4 quarts of motor oil to a tank of fuel a little more? Are we talking cheap 30 weight oil? What should I see when I do and what effect should it have on mpg?

In my case I am suspect of fuel quality as she has fills up at a number of different stations. I have considered picking up some off road diesel and running a tank or two of it to see the difference.

 

[Blood_of_Tyrants]

As far as a diesel engine is concerned, you can use filtered, used motor oil.

 

[4x4 Forever]

I have considered picking up some off road diesel and running a tank or two of it to see the difference.

Just dont get caught, the state revenue boys want their cut. The red dye is a dead giveaway. If you ever take a fuel part (IP, etc.) in and red dye is seen, they are required to call it in, although most places just turn a blind eye.

From what I have been reading, Blood_of_Tyrants idea of using filtered motor oil is good. No need to used the new stuff.

 

[jdemaris]

I have been adding a bottle of 2 cycle oil to each tank but it sounds like that may not be enough. Can you explain the suggestion to add 3-4 quarts of motor oil to a tank of fuel a little more? Are we talking cheap 30 weight oil? What should I see when I do and what effect should it have on mpg?
.

I think you're wasting your time and risking expensive pump damage unless you're very careful (with used motor oil). All the stories you hear about it being historically used for years are pretty much nonsense when put into the context of the 6.2 diesel. That because the 6.2 uses a distributor type injection pump. The big trucks use in-line pumps and an there is a huge difference in reliability, durability, and longevity. A big-rig in-line pump has a separate injection pump for each cylinder. So, if there are 8 cylinders, there are 8 pumps. A "distributor pump" like the 6.2 uses has one tiny pumping section, even though there are 8 cylinders to feed. So, the pump is hooked to a fuel distributor and that is the most expensive part of the pump, and the least tolerant to alternative fuel mixes.

If you carefully use motor oil in your 6.2 fuel tank, you'll burn it off OK, but you're going to gain just about nothing.

In regard to adding lube to the diesel fuel? It's been well tested under controlled conditions. Motor oil gives lousy "added" protection as compared to other things, like two-stroke motor oil. Truck stops, historically did throw waste oil into the big diesel tanks and for that use, it worked fine and got rid of lots of waste oil.

Also, about the myth of the first diesels being run on peanut oil. The first diesels ran on versions of coal and lamp oil. Also, Rudolph Diesel's first successful engine (what we now often call a "diesel)" was the second, not the first. Dugald Clark was first in 1878. Diesel didn't get his going until 1983. And, Clark's first compression-ignition engine later became the platform for the most famous "diesel" in the world - the Detroit supercharged two-stroke.

And, one note about tires. At least in my experience, nothing gives better mileage than small 235/75-15" tires. Bigger tires do drop RPMs, and also give more rolling resistance and more air resistance due to increased vehicle height.
I've had over 20 6.2 powered trucks and never had a single one that did not lose MPGs with bigger tires. If someone's else's experience differs, I have no idea how to account for that since it goes against physics.

Lube additives, In Order Of Performance, best to worst:

1) 2% REG SoyPower biodiesel
HFRR 221, 415 micron improvement.
50:1 ratio of baseline fuel to 100% biodiesel
66.56 oz. of 100% biodiesel per 26 gallons of diesel fuel
Price: market value

2)Opti-Lube XPD
Multi-purpose + anti-gel
cetane improver, demulsifier
HFRR 317, 319 micron improvement.
256:1 ratio
13 oz/tank
$4.35/tank

3)FPPF RV, Bus, SUV Diesel/Gas fuel treatment
Gas and Diesel
cetane improver, emulsifier
HFRR 439, 197 micron improvement
640:1 ratio
5.2 oz/tank
$2.60/tank

4)Opti-Lube Summer Blend
Multi-purpose
demulsifier
HFRR 447, 189 micron improvement
3000:1 ratio
1.11 oz/tank
$0.68/tank

5)Opti-Lube Winter Blend
Muti-purpose + anti-gel
cetane improver
HFRR 461, 175 micron improvement
512:1 ratio
6.5 oz/tank
$3.65/tank

6)Schaeffer Diesel Treat 2000
Multi-purpose + anti-gel
cetane improver, emulsifier, bio-diesel compatible
HFRR 470, 166 micron improvement
1000:1 ratio
3.32 oz/tank
$1.87/tank

7)Super Tech Outboard 2-cycle TC-W3 engine oil
Unconventional (Not ULSD compliant, may damage 2007 or newer systems)
HFRR 474, 162 micron improvement
200:1 ratio
16.64 oz/tank
$1.09/tank

Stanadyne Lubricity Formula
Lubricity Only
demulsifier, 5% bio-diesel compatible, alcohol free
HFRR 479, 157 micron improvement
1000:1 ratio
3.32 oz/tank
$1.00/tank

9)Amsoil Diesel Concentrate
Multi-purpose
demulsifier, bio-diesel compatible, alcohol free
HFRR 488, 148 micron improvement
640:1 ratio
5.2 oz/tank
$2.16/tank

10)Power Service Diesel Kleen + Cetane Boost
Multi-purpose
Cetane improver, bio-diesel compatible, alcohol free
HFRR 575, 61 micron improvement
400:1 ratio
8.32 oz/tank
$1.58/tank

11)Howe’s Meaner Power Kleaner
Multi-purpose
Alcohol free
HFRR 586, 50 micron improvement
1000:1 ratio
3.32 oz/tank
$1.36/tank

12)Stanadyne Performance Formula
Multi-purpose + anti-gel
cetane improver, demulsifier, 5% bio-diesel compatible, alcohol free
HFRR 603, 33 micron improvement
480:1 ratio
6.9 oz/tank
$4.35/tank

13)Used Motor Oil, Shell Rotella T 15w40, 5,000 miles used.
Unconventional (Not ULSD compliant, may damage systems)
HFRR 634, 2 micron improvement
200:1 ratio
16.64 oz/tank
price: market value

14)Lucas Upper Cylinder Lubricant
Gas or diesel
HFRR 641, 5 microns worse than baseline (statistically insignificant change)
427:1 ratio
7.8 oz/tank
$2.65/tank

15)B1000 Diesel Fuel Conditioner by Milligan Biotech
Multi-purpose, canola oil based additive
HFRR 644, 8 microns worse than baseline (statistically insignificant change)
1000:1 ratio
3.32 oz/tank
$2.67/tank

16)FPPF Lubricity Plus Fuel Power
Multi-purpose + anti-gel
Emulsifier, alcohol free
HFRR 675, 39 microns worse than baseline fuel
1000:1 ratio
3.32 oz/tank
$1.12/tank

17)Marvel Mystery Oil
Gas, oil and Diesel fuel additive (NOT ULSD compliant, may damage 2007 and newer systems)
HFRR 678, 42 microns worse than baseline fuel.
320:1 ratio
10.4 oz/tank
$3.22/tank

1ValvTect Diesel Guard Heavy Duty/Marine Diesel Fuel Additive
Multi-purpose
Cetane improver, emulsifier, alcohol free
HFRR 696, 60 microns worse than baseline fuel
1000:1 ratio
3.32 oz/tank
$2.38/tank

19)Primrose Power Blend 2003
Multi-purpose
Cetane boost, bio-diesel compatible, emulsifier
HFRR 711, 75 microns worse than baseline
1066:1 ratio
3.12 oz/tank
$1.39/tank