Dash vs Nav Screen Odometer MPG

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glenski_31
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Dash vs Nav Screen Odometer MPG

Postby glenski_31 » Thu Nov 26, 2015 5:33 pm

Hi All

New to me 2005 Pathfinder LE as per my signature. I have spent a couple of days searching on the forum and haven't been able to find what I was looking for.

I know I bought a 'gas guzzler' but was thinking I could live with 19-20 MPG and so I have been driving around for the first 1/2 running mid grade fuel with the Nav system showing me 12.8 L/100km which is right on par with what I was hoping. I have been driving very very conservatively watching the instantaneous gauge the whole time and am about 70/30 highway driving.

So I fill up and I end up putting in 34L which when I take the Nav system trip ODO (220kms) I get 15.5L/100km which just doesn't add up. That is 20% worse actual mileage than the Nav system states.

I am running 265/65/17 tires which I believe to be the factory size for the LE.

Anyhow this time around I reset the dash ODO and the Nav system ODO and will see if there is a difference. I also reset the Nav fuel meter and will see what the next 1/2 tank yields.

Tire pressure is at 35PSI all around, Running Hercules Terra Tracs, clean air filter, detailed maintenance done by PO. My main issue is where is the discrepancy coming from?

Any thoughts would be appreciated.

Thanks
Glen


glenski_31
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Postby glenski_31 » Mon Nov 30, 2015 10:00 am

Bump...

I did another test this time around and got 14.7L/100km calculated while the Nav system was displaying 12.9L/100km. so 12.3% difference between actual and Nav system.

Has anyone else seen this much of a difference?

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NVSteve
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Postby NVSteve » Mon Nov 30, 2015 11:26 am

The problem with the Nav readings is that they are based on one tire size, and that is obviously not the same tire size you are running. To give you a better idea, the calibrated tire size for the 2007 models is 265/75/16. That means that everyone running a tire smaller than the 265/75/16 will be seeing lower numbers on the Nav than what is happening in reality.

The answer to your second question is no, there is no way to recalibrate to a specific tire size. At least nobody on this forum has found a way, myself included.
Last edited by NVSteve on Wed Dec 02, 2015 10:05 am, edited 1 time in total.

glenski_31
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Postby glenski_31 » Wed Dec 02, 2015 9:53 am

NVSteve wrote:The problem with the Nav readings is that they are based on one tire size, and that is obviously not the same tire size you are running. To give you a better idea, the calibrated tire size for the 2007 models is 265/75/16. That means that everyone running a tire smaller than the 265/75/16 will be seeing better numbers on the Nav than what is happening in reality.

The answer to your second question is no, there is no way to recalibrate to a specific tire size. At least nobody on this forum has found a way, myself included.
Thanks for the reply. Where do I find out the calibrated tire size for my 2005 LE?

If I assume the size above and my wheels are 265/65/17 and the calibrated values on both the dash and nav are for 265/75/16. This make for 3.56% difference in speed. So 100 KPH indicated means I am travelling at 96.6 KPH.

Which means that if 100 KPH for 1h the trip would say I have travelled 100km when in reality I have travelled 96.6 km so Trip is reading 3.56 less KM. Fewer KMs and the same fuel consumption will make for a Nav reading that will be 3.56% low correct?

So I still seem to be off by about 8.7% accounting for tire size.

I will just keep checking my L/100km as I get more and more KMs under my belt.

Thanks again

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NVSteve
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Postby NVSteve » Wed Dec 02, 2015 12:03 pm

glenski_31 wrote: Thanks for the reply. Where do I find out the calibrated tire size for my 2005 LE?
If you have the original 2005 brochure, it will list all the models and tire sizes available. You might be able to find one via Google as well. If that year is similar to 2007, then the largest tire size listed would be the calibrated size. But, your best bet is to contact a few people on this forum with 2005 Pathfinders in their signatures. Ask them what size they run & if it is completely accurate with the speedo.
Which means that if 100 KPH for 1h the trip would say I have travelled 100km when in reality I have travelled 96.6 km so Trip is reading 3.56 less KM. Fewer KMs and the same fuel consumption will make for a Nav reading that will be 3.56% low correct?
Yeah, I had that backwards when I read it again (typical disconnect between brain and fingers). I don't have Nav myself, and have never payed any attention whatsoever to any of the displays available outside the odometer, but I would say you are on the mark. My biggest beef with the "current" mpg readings is that it fluctuates so wildly depending on speed, etc. 8.7% is a pretty huge difference though. Come to think of it, the only really bizarre mpg readings (plus or minus) I have seen posted on this forum have been from members with Canadian models. One guy posted a claim of close to 30mpg, which I absolutely will never believe, while I've seen others posting real dismal numbers. Again, all Canadian models. Sorry I'm not much help, but that 8.7% is certainly an eye opener. Since you have the Nav system, do you also have another display under the speedo that will also show the odo, distance to empty, etc? Or do you have to rely purely on the Nav system?

glenski_31
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Postby glenski_31 » Wed Dec 02, 2015 7:39 pm

NVSteve wrote:
If you have the original 2005 brochure, it will list all the models and tire sizes available. You might be able to find one via Google as well. If that year is similar to 2007, then the largest tire size listed would be the calibrated size. But, your best bet is to contact a few people on this forum with 2005 Pathfinders in their signatures. Ask them what size they run & if it is completely accurate with the speedo.

Again, all Canadian models. Sorry I'm not much help, but that 8.7% is certainly an eye opener. Since you have the Nav system, do you also have another display under the speedo that will also show the odo, distance to empty, etc? Or do you have to rely purely on the Nav system?
I will have to check in the paperwork provided. I think all the original manuals are there. Perhaps there is something that indicates the largest tire size. Will do.

Interesting to note about the Canadian nature of the discrepancy. Perhaps some fellow Canadians can chime in? Perhaps I am the only one crazy enough not to trust what the computer spits out?

I do have the dash trip ODO and the Nav system ODO and I have reset them both at my last fill and they are within 1% of each other so that seem very reasonable. No issues there. What I am curious about is - Does the Nav ODO work on GPS and the dash ODO work on wheel rotation? That would be interesting to know. Anyhow I expect to put some fuel in it tomorrow I will be close to 300km on the trip by the time I fill up tomorrow so will try and keep you posted on what the numbers end up working out to.

It might have been best if I had just believed the Nav system and went merrily on my way. I am really having a hard time with the fuel on this. Beautiful ride otherwise though - lets just say the 2004 Grand Am hasn't moved much since I bought the Pathy.

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NVSteve
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Postby NVSteve » Fri Dec 04, 2015 10:09 am

Okay, so after rereading everything, a question: you are looking at the Nav display which is showing current mileage/fuel consumption, correct? If so, that number can't be relied on for anything, especially if you aren't maintaining a constant speed. It's just a snapshot of that specific moment in time and the fuel consumption at that moment. I've seen mine indicate as high as 30mpg when coasting down from Tioga Pass into Yosemite.

Your 14.7l/100km works out to about 16.014mpg. My overall average for the entire 90,000+ miles I have driven mine is 16.3mpg or so. I personally wouldn't consider that bad. I typically never see anything higher than 18mpg.

glenski_31
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Postby glenski_31 » Mon Dec 07, 2015 9:11 am

NVSteve wrote:Okay, so after rereading everything, a question: you are looking at the Nav display which is showing current mileage/fuel consumption, correct? If so, that number can't be relied on for anything, especially if you aren't maintaining a constant speed. It's just a snapshot of that specific moment in time and the fuel consumption at that moment. I've seen mine indicate as high as 30mpg when coasting down from Tioga Pass into Yosemite.

Your 14.7l/100km works out to about 16.014mpg. My overall average for the entire 90,000+ miles I have driven mine is 16.3mpg or so. I personally wouldn't consider that bad. I typically never see anything higher than 18mpg.
Hey NV Steve. I am looking at the Nav display and trying to compare it to actual numbers. I am not looking at the instantaneous rather the average. I should take a photo of what I am looking at. I realize these things are 'best guesses' and it also would depend on how long the average is stored. Is it the average of the last 200kms or the last 2hrs etc. I assume there is a limited number of storage points.

Yeah I am thinking my MPG isn't that bad either. The one thing that has happened is the engine light came on and coded at P0455 which is a major EVAP leak. I am wondering if this is messing with the computers ability to calculate fuel consumption in some way? From what I gather it may be a solenoid of some sort that the 05s were known for. The gas cap looks to be making a good seal.

Either way the real numbers are the real numbers. Its just nice to know how far off the numbers actually are. I did check my owners manual and the largest tire size is 265/70/16 for that year which if I assume the ODO is calibrated for would mean I have travelled 3.6% fewer kms than the dash ODO indicates and I will always factor that in to my calculated numbers.

I have a 300km highway work trip tomorrow and I am going to take the Pathy and see what she gets on pure highway miles from the pumps and dash trip (including 3.6% error), and nav average.

glenski_31
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Postby glenski_31 » Fri Dec 11, 2015 9:51 am

For those who have been following I thought I would summarize my findings. Thanks NVSteve for your thoughts throughout.

I did two 300+km highway trips this week for work at 110kph and also have a couple of 1/2 tanks of mixed use where I have recorded dash trip readings, Nav trip readings, Nav L/100km, and actual calculated L/100km.

My findings are as follows. The tire size issues is a non issue. The Nav read 358.9km, the dash trip read 360.0 and google maps showed 360km. So pretty hard to say that there is a consistent 3.5% error there due to tire size discrepency. So from here on out I will take what the trip says in the dash as my real number and won't bother to convert. The three sources generally agree.

The Nav L/100 km I found to be on average 12.5% low. On the pure highway driving it was 12% low and when driving mixed use it was 13% low. I will from here on out know that the Nav is reading 12.5% less on average fuel consumption than what is really going on.

Also to note the average for the last 1300kms has been 13.4L/100km or 17.5MPG. On the highway at 110kph the fuel economy was 12.8L/100km or 18.3MPG both of which I am reasonably happy with. All of this was done with premium fuel. My next round of testing will be with regular fuel and see if it is worth the premium in the beast.

Hope someone in the future finds this as useful summary.

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NmexMAX
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Postby NmexMAX » Fri Dec 11, 2015 10:02 am

I can attest and mine is quite the Frankenstein set-up. (35" tires/3.36 gears).

My MPG's are very accurate as is the miles to empty.


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