MPG's going down, is it the new fuel?

[GMichaels]

Have a 1997 3500 4x4 with 4:11 and 5sp. put in a 10 plate and a gov kit.



when I first purchased this truck I was getting 15. 5 mpg. I thought that was low so I changed the fuel filter, cleaned the prefilter, checked for fuel leaks, changed the pressure valve on the pump. no change so I just accepted that this is what the truck's mpg's are. i didn't check the timing due to the cost. but the truck runs so nice, boost is good and egts are normal.



now I am getting 12. 5 mpg's and figure something must be wrong. could the low sulpher fuel be adding to the problem? Is there any other way to tell if the timing has slipped? I figure at some point if the mpgs keep going down the problem should become obvious.







I had a 1993 5spd 2wd 3:50 that got 22 mpg.

 

[Vaughn MacKenzie]

You probably meant to put this in the 12-valve forum but my two 12-valves ('96 & '98) have been getting considerably worse MPG this winter than the past 2 winters.

 

[Bekim]

Have a 1997 3500 4x4 with 4:11 and 5sp. put in a 10 plate and a gov kit.

when I first purchased this truck I was getting 15. 5 mpg. I thought that was low so I changed the fuel filter, cleaned the prefilter, checked for fuel leaks, changed the pressure valve on the pump. no change so I just accepted that this is what the truck's mpg's are. i didn't check the timing due to the cost. but the truck runs so nice, boost is good and egts are normal.

now I am getting 12. 5 mpg's and figure something must be wrong. could the low sulpher fuel be adding to the problem? Is there any other way to tell if the timing has slipped? I figure at some point if the mpgs keep going down the problem should become obvious.



I had a 1993 5spd 2wd 3:50 that got 22 mpg.

According to Chevrons ULSD page the new fuel is slightly higher cetane. They add stuff to maintain the same lubricity ASTM standard.
Fuel should not be the culprit here IMHO
Mike
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[Bob Cochran]

Perhaps ULSD should not lower MPG, but mine has went down and I have done nothing to truck to cause it or driving any different. So if not ULSD; I am confused that is probably normal for me though.

 

[cerberusiam]

According to Chevrons ULSD page the new fuel is slightly higher cetane. They add stuff to maintain the same lubricity ASTM standard.

Fuel should not be the culprit here IMHO

Mike

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The cetane and lubricity of the fuel have nothing to do with the important part of the fuel that is now missing, BTU's. Cetane is a measure of ignition and combustion speed. The higher the number is the quicker it will light and burn, which is directly at odds with what makes good mileage with diesels.



In the process of removing the sulphur the aromatics and long chain molecules were also removed which drops the BTU's available in the fuel. Less BTU's equals less heat which is less HP. This leads to more fuel to maintain the needed HP and less mpg.



The mpg's started dropping when the new fuel was introduced and they have really dropped with the colder weather. Boost is up, EGT's are down along with the mileage.



Before the new fuel was introduced it was predicted mileage would drop a bit. That is pretty much what has happened. :{

 

[FATCAT]

You are correct sir ... my '97 is getting about 1 mpg less then this time last year, but the BIG difference is in my VW Jetta TDI. I am now down to about 49 mpg from 52 (same time last winter).



This fuel is definitely the culprit ... but also, replace your fuel filter. I have heard some folks say that this new fuel will clean out old tanks and dredge up stuff like bio-diesel does ... so, change your fuel filter a few times before the winter is out.

 

[DOWG]

The 2006 5. 9 took a big dive in MPG's on the last tank; my stock tank is 36 gallons and the auxillary tank (last tank) is 40 gallons.



I hope it is clogged filters; my American Tank in-tank lift pump's (both tanks) have normal idle @ 17 psi and normal WOT @ 10 psi.



After the big dive in MPG's, normal idle was also @ 17 psi and now WOT is @ 5 psi. And now my fuel rail pressure also started flucuating a lot more than it usually does.



I did not calculate the MPG's, but simple Aggie math showed it was way off.

 

[klenger]

My in-town milage has gone up from about 20 mpg to about 21 mpg since the new fuel came out. Go figure. In any case, I'm happy.

 

[Vaughn MacKenzie]

I just computed the last several tanks' MPG for my '96 and it's definitely down compared to this time last year. I would say just a little over 1 MPG.



Vaughn

 

[GMichaels]

ops put this in the wrong area, sorry about that.

 

[KD7GYJ]

Yea, I've noticed the same with my truck. It's really bad with highway driving. The last couple of tanks, I have been getting 440 miles on 30+ gallons. I am usually around 550 or 600+ on 30+ gallons of fuel.



Something's happening.

 

[Bekim]

The cetane and lubricity of the fuel have nothing to do with the important part of the fuel that is now missing, BTU's. Cetane is a measure of ignition and combustion speed. The higher the number is the quicker it will light and burn, which is directly at odds with what makes good mileage with diesels.

In the process of removing the sulphur the aromatics and long chain molecules were also removed which drops the BTU's available in the fuel. Less BTU's equals less heat which is less HP. This leads to more fuel to maintain the needed HP and less mpg.

The mpg's started dropping when the new fuel was introduced and they have really dropped with the colder weather. Boost is up, EGT's are down along with the mileage.

Before the new fuel was introduced it was predicted mileage would drop a bit. That is pretty much what has happened. :{

Good info! The 1% drop in BTU's should not be causing more than tenths of a mpg in decreased mileage. It's funny how when people notice the new sticker on the pump, they talk about losing 2-3 miles per gallon. Here in CA, most stations have been selling ULSD since August, and now ~4 months later people are noticing the label and talking about drastic reductions in mileage(and sometimes performance)
True I too have noticed a minimal loss of mileage(between 2 and 3 tenths mpg) averaged over the 10,000 commuting miles since ULSD intro.

Energy Content:
In general, the processing required to reduce sulfur to 15 ppm also reduces the aromatics content and density of diesel fuel, resulting in a reduction in energy content (BTU/gal).


<LI>The expected reduction in energy content is on the order of 1% and may affect fuel mileage.


Cetane Number: In general, the processing required to reduce sulfur to 15ppm also reduces the aromatics content resulting in an increase to the cetane number.

Q. How will ULSD fuel affect the power and fuel economy of existing diesel cars, trucks and non-road engines and equipment?

A. Under typical operating conditions, there should be no noticeable impact on overall power using ULSD fuel. * Fuel economy may be reduced slightly because
the process that removes sulfur also can reduce the energy content of the fuel.


Above are quotes from the Chevron ULSD FAQ, and the Clean Diesel Fuel Alliance Organization. One is profit driven, the other consumer driven. Notice how both state the same facts
Mike
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[cerberusiam]

The expected reduction in energy content is on the order of 1% and may affect fuel mileage.



Yikes! That 1% reduction in fuel energy really gets multiplied when it burns.



Rough estimates put my mpg loss at 10%. Several trips from Idaho\Washington to SoCal last summer and the mileage dropped 10% as soon as we fueled in CA. The same happened in Oct when we finally were switched to the new fuel in ID then when it got cold it dropped even more.

 

[KD7GYJ]

Now we have winter fuel to contend with, with the introduction of ULSD coming into play about the time there was a change to winter fuel.

 

[Vaughn MacKenzie]

New thread to check out https://www.turbodieselregister.com/forums/showthread.php?p=1661155#post1661155

 

[AGrubbs]

Winter fuel

I think a lot of places are getting winter fuel. That might be a big part of it.

The BTU difference in #2 to #1 is more than the difference in LSD and ULSD.



I usually like to run #2 with additives or 80-20 fuel with additives if its very cold. But yesterday I happened to see a small sign where I fill up that said they were running 50-50 fuel. I wouldn't have caught that if I hadn't been looking for some 'tater chips which were right by the sign (about 1/2 size of a regular sheet of paper) in the window. I'll go to the other place to get my fuel till spring. They have pumps for #2 and winterized diesel both.

 

[Bekim]

I think a lot of places are getting winter fuel. That might be a big part of it.
The BTU difference in #2 to #1 is more than the difference in LSD and ULSD.

I usually like to run #2 with additives or 80-20 fuel with additives if its very cold. But yesterday I happened to see a small sign where I fill up that said they were running 50-50 fuel. I wouldn't have caught that if I hadn't been looking for some 'tater chips which were right by the sign (about 1/2 size of a regular sheet of paper) in the window. I'll go to the other place to get my fuel till spring. They have pumps for #2 and winterized diesel both.

YUP!
Mike
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