Fuel economy

[Jon Wehrenberg]

Dale,

Here is the gauge I have monitoring my air filter condition.



Prevost lists three different part numbers for the item described as an air restriction gauge or air restriction indicator. They are 530121, 530161, and 530193. I suspect a parts house will have the same gauge. On my first coach the gauge did not have the rubber hose, but screwed directly into a threaded fitting in the intake pipe.

[MangoMike]

Well, since post bling, obviously the pix was taken w/ available lighting.

I'm blindid' by the light

MM

[dreadnought]

is that a run in the paint I see behind the restriction guage? on Jon's bus? shock!

[Joe Cannarozzi]

Isint a dash guage available? Hmmmmm, something Liberty actually doesnt have?

[Jon Wehrenberg]

It's a run in the paint. What can I say? The bling contest is over, I am licking my wounds, and I have stopped polishing my slack adjusters and worrying about runs in the paint.

[Petervs]

OK, so I am a new member, and what right do I have to comment about the comments anyway. But I just have to .

I started this thread with some technical details about fuel economy so we could all have a few facts to bat around. It did not take very long for the discussion to degenerate into sniping about paint runs on the air filter housing. Now really guys!!!

Actually, my original post was not trying to make any kind of suggestion about how fast we should drive or why, but it was meant to provide data so we would know what the performance of our rigs was at various speeds, and how that performance changes with speed. Anyone can draw their own conclusions and drive accordingly.

I do need to speak out and refute a post by LEWPOPP, he said: "
I change the air filter every year and am amazed how the mileage increases easily a few tenths. I normally don't drive in too many dusty areas but a lot of air is sucked thru that system." I do not think this statement is correct and here is why.

The diesel we burn becomes energy expended in various ways, such as
1. Overcoming tire friction with the road.
2. Heat out the radiator and radiated from the warm engine parts.
3. Heat out the exhaust.
4. Overcoming friction of all the moving parts on the coach.
5. Power to the wheels overcoming air resistance.
6. Noise.
7. Power used to accelerate.
8. Power used to gain height as in climbing a grade.
9. Some small amount of diesel might not be burned at all and just goes out the tailpipe.
10. Overcoming the forces created by the air entering the intake until it exhausts. This is where a dirty air filter would cause problems. But a look at the ways diesel energy is used above and you will see overcoming the resistance of the air filter is a trivial part of the total. And only if the engine were running at wide open throttle. Any less than that and the resistance of the filter is but a microscopically trivial part compared to the rest of the air flow path. A dirty filter would prevent the engine from developing full rated power, but it would not really increase the fuel consumed because the amount of fuel injected is controlled by the DDEC to match the amount of air sucked into the cylinder. The engine will not run "rich" just because the filter is restricting air flow a little bit.

If you think the air filter does reduce the milage, then the best answer would be to remove it completely, especially if you were not in dusty conditions!

I think the mileage data I generated really does show that you can affect your tank to tank fuel mileage by a few tenths of a MPG very easily, and that is by varying your cruising speed a little bit. Of course my numbers reflect best case, fairly steady state cruising down the interstate. If you are in traffic, driving in town, driving in hilly areas, or any conditions that require more frequent speeding up and slowing down then your overall mileage will go down.

I hope my explnation makes sense, anyone is encouraged to let me know politely if they think I am full of beans from all the mexican food at POG 2. I think this forum will only be useful if we all try to keep the details as correct as possible.

And please, no one try to convince me I will get better mileage if I fill my tires with nitrogen either.

Regards to all

Peter vS
1994 Marathon XLV

[MangoMike]

Peter,

Sometimes these posts wander around a bit, get joked up and smacked down, but in the end invariably, like cream rising to the top, good information does surface. Like yours did.

The non-informational comments keep readers coming back. Like watching a train wreck or me leaving a Jimmy Buffett concert.

Thanks for participating.

Mike

[truk4u]

Peter,
I like to coat the front of my bus with a light film of Mango's french fry oil and pick up a couple tenths per gallon.

[MangoMike]

...and there you go.

[rfoster]

Pic taken from the windshield crossing Texas on I-10 running fast enough not to get run over, 7.92 mpg

CIMG1764.JPG
But hey I decided to get home by Sunday nite!