fuel mileage question

bigmaho · **Posted:** Wed Sep 10, 2008 10:54 pm

Hi Guys (and diesel gals), I'm new onboard here. I have an red 06 CRD, 41000 miles (24K are mine). I use it to tow a 3500 lb cargo trailer from NY-NM and when out in NM for hitting those great back country tracks. Anyway, I keep seeing widely varying mileage claims here. While I'm doing better than a gas Liberty, my mileage isn't all that great. I get 22 driving fairly easy on the hwy (65-70 according to my GPS), and only 16 when towing. Should I be doing better? I buy B20 locally and regular diesel on the road.
So far, except for my first week in the CRD when it all went to hell, I love the little beast. 1st week my torque converter died on I70. Had to get towed into Terre Haute Indiana and sit there for 2 days. Made it to Taos, NM and then the fuel system went. Both were repaired under warranty. Since then it's been fine.
Billy

nursecosmo · **Posted:** Wed Sep 10, 2008 11:18 pm

Welcome to our little site. We like to have a lot of fun with banter and throw insults at each other, but it's all in good spirits. There has been some discussion about some of the 06 models getting slightly lowered MPG but it might just be in our heads. There is a lot of variation between individual vehicles all the way from 18 to over 30. Driving style has a lot to do with MPG as well as all of the little things like increased tire pressure, cleaning the MAP sensor, doing the ORM and so fourth. I average 25 between town and highway. Check out the tech section for suggestions.

bigmaho · **Posted:** Wed Sep 10, 2008 11:41 pm

Doing the ORM? Orm means worm in Swedish. I have to dance like a worm in front of my CRD to improve mileage.... Well... ok, but no pictures...
Thanks for your response and the heads up on the group (though I belong to a couple of professional groups that can go well past 'heated'). But what is the ORM?
Thanks,
Billy

nursecosmo · **Posted:** Thu Sep 11, 2008 12:11 am

Off road Mod. Just pull the MAF sensor plug. The search function works great in this forum.

geordi · **Posted:** Thu Sep 11, 2008 1:51 am

Chances are, the MAP sensor is also a solid block of crud in there. Pull that and clean it completely, and you should find yourself the happy owner of a few more MPG.

Strongly consider getting the SEGR as well. ABSOLUTELY worth the investment.

As for the mileage while towing, 16 is low for that little bit of weight. I've pulled as much as 7000 with my CRD, and got 18mpg solid at 60-65mph. I also pulled a 6x12 enclosed trailer with a weight of about 4000 total, and got 19-20 all the way up and back from Savannah, Ga to New Hampshire - via Albany and Boston. Not bad for a little 4-banger!

Other things to do: Get yourself some larger tires. NOT WIDER, taller. I've stuffed 215/85/16 BF Goodrich Commercial shoes into mine, and they take off about 200 revs per mile or so. It adds up. Those will fit fine without a lift kit, no rubbing at all. Either way, inflate them to the sidewall max. Thats good for at least another mpg or two.

Remove the muffler and replace it with a Flowmaster - Much better response and coasting capabilities. I take no responsibility if you also remove that 50 lbs of cat... But I don't have to get emission tested here.

Welcome to the group!

Joe Romas · **Posted:** Thu Sep 11, 2008 6:52 am

Good advice on cleaning the MAP :wink:

Actually it's not a few of the 06's getting lower fuel mileage, it's some of the older 05's getting better or what they should be getting :lol:

It's been recently determined some 05's have a fan clutch that sucks less cooling air. This results in overheating in some conditions but puts far less drag on the engine that might explain some of the difference in fuel mileage.
My driving is on the easy side and at 19k mine is not broken in yet and my all time best was 25 mpg. But when towing our 17' 3200-3500 pound camping trailer I get around 19. 20 to 22 is norm for my routine driving.
You definetly want to check into what EGR is doing to your intake then deside what you want to do. ORM (unplugging the MAF) gives a cel. EORM involves cutting wires in the main harness and scared me away. Now it's been pretty much verified (by several owners) that blocking the EGR with a plate and removing the butterfly plate from the FCV gives no cel, easy to do and put back if needed and results in no egr flowing and more power :wink:

Lots of good information on these pages but a lot of reading. Sounds like the PO of your CRD got discussted with the lousey dealer service not being able duplicate problems that came to a head for you

US dealers know very little about these fantastic machines but you've become LOST and after 3 years or more, most problems have been found and solved here

bigmaho · **Posted:** Thu Sep 11, 2008 7:39 am

Great info! Thanks guys. I'll pull the MAP sensor this weekend. I'm also running 40 lbs in non-stock tires rated to 60 lbs, so I'll add some more air. Thanks!
Billy

warp2diesel · **Posted:** Thu Sep 11, 2008 7:40 am

All of the tricks posted are good and I have done them and recommend them.
One deep dark little secret is the odometer reads 10% low in my '06 and many others with stock tires. So if you have stock tires chances are that yours is reading 10% less in the miles and that throws off your MPG calculation by the same.
Check your odometer since you do some distance hauling and verify the error. I used a GPS, MicroSoft Streets and Trips, and drove on a previous route that was measured with a car that had a certified odometer that was dead on. All three indicated that my odometer was reading 10% low.
Also the speedometer reads 5% fast.

I still love my little tractor.

bigmaho · **Posted:** Thu Sep 11, 2008 8:32 am

As you say, my odometer is off about 7%. I use my GPS for all speed and mileage calculations.
Thanks

DarbyWalters · **Posted:** Thu Sep 11, 2008 2:05 pm

I have tracked my mileage for just under a year. I have an 06 with the OME lift and slightly taller/larger tires (235/75/16). I also added a full skid setup but they are aluminum and don't weight too much. I drive 90% city...stop n' go...with a little highway and some towing. I have averaged 20.8mpg and am happy with that.

If I drive strictly highway and keep speeds at 64-68 mpg (GPS)...I can get ~ 26-28mpg. I do adjust my odometer reading by the 6% it shorts me...caused by odometer error and taller tires.

mark2m · **Posted:** Thu Sep 11, 2008 4:22 pm

I'm getting 28-30 mpg on my CRD. As read from the EVIC but I haven't verified that. Seems accurate though. I drive over 80 miles a day. Half is highway and the other half is local roads. It is stock except for the ORM. Also I hear some guys saying to raise their tire pressures to max inflation. While that will give you better mileage it also wears your tires down in the center quite a bit faster. Pay less for diesel now but change your tires more often. You decide. Also you get a decrease contact patch. Keep in mind that reommended tire pressure it 33psi. That is not much.

DOC4444 · **Posted:** Thu Sep 11, 2008 4:27 pm

Darby,

Is you exhaust 3" from the the Turbo back or?? Do you have a CAT at all? If so is it aftermarket 3"? Do you have any sort of muffler?

Thanks in advance for you input.

DOC

geordi · **Posted:** Thu Sep 11, 2008 4:42 pm

mark2m wrote:

I'm getting 28-30 mpg on my CRD. As read from the EVIC but I haven't verified that. Seems accurate though. I drive over 80 miles a day. Half is highway and the other half is local roads. It is stock except for the ORM. Also I hear some guys saying to raise their tire pressures to max inflation. While that will give you better mileage it also wears your tires down in the center quite a bit faster. Pay less for diesel now but change your tires more often. You decide. Also you get a decrease contact patch. Keep in mind that reommended tire pressure it 33psi. That is not much.

Sadly, this is misinformation, spouted by the people that want you to return to both the fuel station and the tire shop as often as possible. Car manufacturers don't make tires. They CHOOSE the cheapest tire FOR THEM to put on the vehicle, that has a load rating *just high enough* to cover the expected weight of the vehicle.

That is why on a vehicle as heavy as the KJ is, they CHOSE Goodyear PASSENGER CAR TIRES that just barely could handle the weight, and then chose an extremely low pressure that exaggerates the contact patch and makes the handling mushy. Oh, Im sorry... It makes a JEEP attempt to "give you a soft, car-like ride"

Yea.

Physics says that for a given load of vehicle, the contact patch will be a constant above a certain minimum pressure. Below that pressure, the contact patch will extend lengthwise, with no discernible benefit in tire life. Quite the opposite in fact. If a tire has excessive sidewall flex due to a pressure significantly lower than it's designed maximum, the tire will heat up, and fail sooner.

Finally, I am driving proof of the fallacy of the "wear down the center first" argument. I have over 20,000 miles on my 215/85/16 commercial highway tires now, which are 80psi load range E tires. I have run them at 80psi, and they are currently at 60psi. The rear tires are showing more wear than the front tires (I have not rotated them, and will not rotate them) but they are wearing SQUARE. The center is no thinner than the shoulders.

I don't ask anyone to believe me personally. I'm only another faceless voice on the internet. But make an honest experiment for yourself. Try running your tires at the sidewall max for an honest 10,000 miles. Make some measurements at the beginning (Photos of a penny in the tread are a good option) and at the end. See if there is any obvious difference. I will say, wider tires that some KJ owners choose will probably distend more in the center than the narrow truck tires I have might. But my tires are also BUILT for high pressure. Don't run ANY tire above it's sidewall max, and it will be doing exactly the work it was DESIGNED to do, while riding square.

blake1827 · **Posted:** Thu Sep 11, 2008 5:36 pm

DarbyWalters wrote:

I have tracked my mileage for just under a year. I have an 06 with the OME lift and slightly taller/larger tires (235/75/16). I also added a full skid setup but they are aluminum and don't weight too much. I drive 90% city...stop n' go...with a little highway and some towing. I have averaged 20.8mpg and am happy with that.

If I drive strictly highway and keep speeds at 64-68 mpg (GPS)...I can get ~ 26-28mpg. I do adjust my odometer reading by the 6% it shorts me...caused by odometer error and taller tires.

Like Darby I've been tracking my mileage you can get a good idea of what others are getting here (mine is CO w/ most recent data 09/07/08 I've done ORM & B20 on all my tracked results): https://www.fueleconomy.gov/mpg/MPG.do?action=mpgData&vehicleID=22529&browser=true&details=on

nursecosmo · **Posted:** Thu Sep 11, 2008 5:51 pm

2X what Geordi said about tires. The PSI range given on auto Tires is the range that the tire can be ran at without tread bulge or deflection within the load range of the tire. However in truck tires, the meaning is widely misunderstood, "Max Load/Max Pressure" is not the pressure at which the tire will burst. Instead, increasing pressure beyond this point results in no additional load-carrying capacity beyond that stated. Nearly all modern radial tires are constructed in such a way that the tread face cannot bulge out significantly before the sidewall fails anyway. Since our Jeeps are very heavy for their size they should be inflated to at least max pressure listed on the tires. Exceptions are of course for off road and conditions like snow etc. By keeping tires at max psi there is much less heat generated through sidewall flex, as well as less friction loss from a shortened footprint. These effects increase MPG as well as increasing tire life but cause more noise and harshness on the highway as well as slightly decreasing straight line traction and breaking ability.

ATXKJ · **Posted:** Thu Sep 11, 2008 6:35 pm

FYI - the quick check on tire profile is to draw a chalk line across the tire - drive 50-100 ft and see where the chalk is gone - tire wear will match the chalk - you want the highest pressure where the chalk disappears across the entire surface.

However - point of physics - the contact patch on the road will match vehicle weight and tire pressure.
i.e. if you have 40psi - you have 1 sq inch of rubber for every 40 lbs of vehicle if you have 33psi - you will have 1 sq inch for every 33 lbs of vehicle. The shape of that contact patch is controlled by the tire design - but not the size - that is weight and pressure only.

The time you will notice this is on emergency stops - when the tire is at maximum traction - you will stop faster at 33psi than you will at 40. - it may be minor and you'll only see it at the limit of available traction - but the difference exists.

DarbyWalters · **Posted:** Thu Sep 11, 2008 6:58 pm

My 3" is cat back with no muffler for the person who asked...

mark2m · **Posted:** Fri Sep 12, 2008 6:43 pm

As ATXKJ stated drawing the chalk line across your tire is the best way to judge how much pressure you should inflate your tires to. Not that I'm trying to be argumentative here. I've always been taught, read and believe that an over inflated tire will cause a smaller contact patch and wear the center of the tire more. Just as an under inflated tire will cause the outside of the tire to wear and hurt your mileage. The decrease in rolling resistance of an over inflated tire is what I understand to help increase your mpg. The max inflation pressure written on your sidewall is max inflation for maximum load capacity of that tire. If the same tire is fitted to a lighter vehicle compared to our Liberty the recommend pressure will be less and the opposite is true. What is written on your door jamb is recommend with OE tires for the weight of the vehicle for optimum ride comfort, handling, mpg and wear. I completely agree you will see better mileage with the tires at max psi. You can increase a few psi for better mpg with no ill effect I believe except for a harsher ride but I think once you start getting up to max inflation you will see increased wear. Hell if I've been led wrong I'm open to accept that no problem there. I'd rather get better mpg and not wear my tires quicker.

Taken from Goodyear's website.
http://www.goodyeartires.com/kyt/tireSafety/properInflation.html

Proper Inflation

Maintaining proper air pressure is the single most important thing drivers can do for their tires. In the space of just one month, a tire can lose two pounds of air pressure.

It is important to check the air pressure of your tires regularly to make sure your tires are neither under- nor overinflated.

Underinflation is the worst enemy your tire can have. It causes increased treadwear on the outside edges (or shoulders) of the tire. It also generates excessive heat, which can reduce tire life. Finally, it reduces your fuel economy by increasing rolling resistance — soft tires make your vehicle work harder.

Overinflation is also detrimental to the tire. Too much air pressure causes the center of the tread to bear the majority of the car's weight, which leads to faster deterioration and uneven wear. Any kind of uneven wear will shorten the lifespan of your tires.

To find the proper air pressure for your tires, look in the vehicle owner's manual, on the sticker on the driver's side doorjamb or in the glove box. If you buy new tires, be sure to learn the correct pressure from your tire Retailer or the owner's manual of your vehicle. Check your pressure at least once a month, and use a high-quality air gauge

Tire Rack
http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=1&

You can find the same thing on other tire manufactures sites also.

warp2diesel · **Posted:** Fri Sep 12, 2008 7:55 pm

I have carried more than the recommended pressure for years and have not had the center of the tread wear faster. One factor is that I drive mostly on expressways at 65+ MPH. As the tire goes faster there is more centrifugal force exerted by the side walls to the road at the outside of the tire contact area. To compensate for this, the tire pressure should be increased so that more pressure is transferred across the full width of the tread.
If all you ever do is the rush hour crawl and never get up to speed, you will want to run at a lower pressure than what you would run at higher speeds.
To put this into perspective I run my stock tires at 40 PSI front and rear on the CRD and 36 front 34 rear on my Wife's TDI.

bigmaho · **Posted:** Sun Sep 14, 2008 10:45 pm

THANK YOU!!!!
I only made a couple of changes. Didn't have time to pull out and clean the MAP sensor, but I unplugged the MAF sensor and added a little more air to my Wranglers (they are rated for 65 lbs, they were at 40, I increased to 50). I drove 100 miles and got 25.5 mpg, up from 22 at best. so the price of diesel just went down about 15%. I owe you all a beer.
Thanks again,
Billy

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