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Hybrid Vehicles Nissan Altima Hybrid Nissan Altima Hybrid
321 messages, Last post on Nov 19, 2009 at 9:31 PM
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Replying to: mazda6dude (Jan 08, 2008 3:13 pm) Mileage differences go back to that discussion we had about how you fill your tank. The nozzles on gas pumps are pretty variable, even within the same gas station. Some will click off too soon and some will actually click off too late, even going as far as to spew fuel on the ground (most drivers have probably experienced that). That can account for up to a gallon, even two, difference in the fill. The principle of a gas hose is that it clicks off when backpressure gets high enough. High backpressure indicates fuel touching the end of the hose (full tank). The problem, especially in California, is that there is a gas vapor recycling system (that's that accordion-like thing on the hose). If it is plugged, or if the hose slips out of the car even slightly, the pump will click off. Additionally, the sensors that sense the backpressure don't have any real standard, and can click off the fuel flow in a wide range of variables. You may THINK you have a full tank, but you may not actually have that. I myself was on a trip a few weeks ago. Was filling up at some little gas station down in mid-state. That pump would NOT fill my tank past 3/4 full for some reason. Something wrong with the sensor on the hose. If I'd calculated my gas mileage there, I would have had some pretty strange numbers. So, here's a scenario that would affect gas mileage..There's all kinds, but this one would probably be common. You fill up your tank. The pump clicks off too soon. You get 10 gallons into the tank, then look at your trip meter, which shows you've gone 400 miles. You think your gas mileage is 40 MPG. OK. Now you drive for a while. You fill up again after 400 miles. This time the pump works correctly. You pump 12 gallons of gas (10 gallons, plus the two you missed in the last fill-up due to the early shut off) You do your calculations. They show you've gotten 33.3 MPG. The reality is that your car is getting about the same gas mileage, but because of variability in the fill ups, you're showing a significant difference in mileage. How do you fix that? Well, there's not really any way to fix it, other than to be really sure your tank is actually full (several clicks, and jockeying the hose in the filler pipe a couple of times will reduce the problem I just discussed, but not completely). By the way, on my NAH, I've noticed that the fuel gauge is pretty accurate. When it's showing 1/2 tank, I pump 10 gallons (assuming the pump is working right). That being the case, the range (which is, as you know, the car's calculation of how much range you've got left, based upon your average mileage, and the amount of fuel you have left) should be pretty accurate. Now an interesting thing about your story is that you say your mileage range shown by the car's computer decreases in the city. This would indicate that your city driving doesn't stay in EV much. EV is where you'll get the big numbers. A car using it's ICE (Internal Combustion Engine) gets the crappiest mileage in the city, because acceleration and stop/go driving is what hammers gas mileage. Every time your ICE kicks in, in city driving, your range will decrease, since your hybrid is behaving more like a conventional car at that point. It's tough to stay in EV mode, especially with someone crowding you from behind, but staying in EV mode is necessary to get those long ranges, and "upsidedown" mileage numbers that hybrid cars are known for (big city mileage, not as good hiway milage). One final comment (at least for now..haha). If you suspect that something isn't working right in your car, there ARE situations where something might be misbehaving, and your dashboard trouble lights won't illuminate. If you think you've got a problem, take your car in and get the Nissan folks to put it on the scanalyzer. If something is wrong, your car's computer will let them know, when it talks to the scanalyzer.....
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Replying to: hiwayman (Jan 09, 2008 12:00 pm) Thanks for the explanation. I just might take it in for a scanalyzer and find out what is going on. One time I filled up the gas and it was full, but the fuel gauge didn't show that until a few minuted into driving. I thought something was wrong with the fuel gauge. Also, I figure out my MPG by doing my own calculations. You are totally right about EV mode. First, its hard to stay in EV mode and second, people crowd up behind you. I try to stay in EV mode whens its possible, but most of the time, I keep a constant smooth speed. I have already had one problem with my NAH and that was the car was pulling to the right. The dealer fixed the problem, but no after I filed a claim with BBB and went through tremendous hassle. Actually, I have never spent so much time on any of my cars trying to fix a problem until I has this problem with my NAH (pulling to the right.) I still believe the problem is not fixed because the shop foreman couldn't guarantee the problem was not going to comeback. |
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Replying to: mazda6dude (Jan 08, 2008 3:13 pm) I think it all depends on the pump. There were some places where I could put in an extra gallon after the first click. and then there were other places where gas spews out right after the 1st click. I don't think your long-term gas mileage is really affected by this as it all gets weighed out in the end |
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Replying to: hiwayman (Jan 08, 2008 2:31 pm) Don't make the assumption that the odomenter is correct. Using my GPS, which I believe is very accurate, I've determined that my NAH odometer is off by about 2+% - under reporting. That's about the same difference between manual calculations and the computer. I was driving south on 495 in MA and the GPS said 50 miles until the next turn at my exit. I reset the trip meter and when I arrived at the exit 50 miles later the trip meter was reading about 48.5 miles. |
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Replying to: saabgeorge (Jan 13, 2008 7:02 am) I drove my NAH with GPS directions on a highway. I had a second portable GPS I just bought as a gift for my dead but wanted to test it first; at the same time, 2 miles before an exit, NAH GPS says "exit in 2 miles", the portable GPS says "exit in half a mile". Maybe an extreme example but this discrepancy did happen couple of times. I'm not saying your GPS is not accurate but I don't think it's a valid measuring tool no matter how great it is. 'Drive by wire' GPS, such as in NAH, would be probably better, as if you loose a signal it still shows your correct location. I drive Holland Tunnel from NY to NJ daily and it shows precisely where you are at all time. If you come out of tunnel and get a signal again, the car icon doesn't even have to adjust itself, it points exactly where you are. Pretty cool. But I guess we can leave GPS talk to another forum...
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Replying to: karolpl7 (Jan 14, 2008 6:04 pm) I use a GPS receiver/logger connected to TomTom Navigator 6 on my Treo 755p. The GPS sends lat, long and measured speed to the software. The speed is displayed on the screen. As a longtime GPS user, I know that the speed from the GPS receiver is the most accurate. Having said that, when I used my portable GPS in our NAH, I found that the speed readout on my portable GPS matched the speedometer. Assuming that the odometer and speedometer are tied together, I believe the NAH odometer is accurate. On my RAV4, the speedometer indicates about -1-2 relative to the GPS readout. Regarding the differences in "distance to a turn," that is a software based algorithm that is dependent on the mapping database. The system may use a plus or minus 50 yards to give a warning, depending on the system being used. Accuracy is not as important. |
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Replying to: karolpl7 (Jan 14, 2008 6:04 pm) When using the GPS, as I described to check my odometer, it's the map data that determines the distance between two different points such as my starting point and the end point, which was my exit. The map data, in my opinion, is pretty accurate - similar to the maps you'd find on MapQuest. These are the detailed maps that you have to load - not the base map. The GPS just determines how close you are to the starting point and how close you are to the end point when you get there so, at the worst, it would be no more than 400 ft off. My odometer was like a mile and a half off. |
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Replying to: saabgeorge (Jan 13, 2008 7:02 am) |
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Replying to: saabgeorge (Jan 13, 2008 7:02 am) GPS is, of course, actually a military system. There are two levels of accuracy transmitted by these GPS "constellations" (groups of GPS satellites). The military broadcast is accurate down to about a yard, or even less, depending upon other factors (I'll get to those in a sec). The civilian broadcast is much less accurate, and the military actually imbeds what's called a "dither factor" into that signal, so that the accuracy continually changes from a yard or two, to easily dozens of yards. This is to prevent a foreign nation from using our own technology to guide their weapons. What you will see in civilian GPSs of ANY kind or maker, is a changing accuracy caused by this dither factor. But wait, there's more! GPS accuracy is also depended upon the number of satellites your unit can "see". The minimum number of GPSs your unit must be able to see to get lat/long and atiltude are 4. Cheap GPSs, then, often have just 4 channels. But your GPS can be a lot more accurate, if it can see more satellites. Thus, good GPSs often have 12 channels. Now here's the rub. GPS satellites are not geosyncronous, meaning they do not stay in the same place in the sky at all times, like TV, weather, and communications satellites do. So, at any given time, there will be a number of GPS satellites in the sky, with others popping up over the horizon, and others going out of sight over the horizon. Your GPS unit keeps track of where these satellites are supposed to be with something called ephemeris data (it's a file that uses time of day and lat/long of the unit to generate a sky map for the GPS of where the birds are). Downloading this file from a satellite is why your GPS takes longer the first time you turn it on, or after it's been stored for a while. The accuracy of that ephemeris data and how it is updated is actually closely guarded by GPS manufacturers. It is the keys to the kingdom, so to speak. Becasue of all these factors, your GPS, ANY GPS (without the inertial navigation system that NAHs have for tunnels and deep valleys) will have varying accuracy from day to day, and yes, even from minute to minute. Interesting side note here. In the beginning of the second Gulf War, when we weren't sure when the military was actually going to attack, I had my GPS turned on. It's an older Garmin model which displays the dither factor. Minutes before the first cruise missles slammed into downtown Bagdad, we saw the dither factor go nuts. We knew something was about to happen. OK. So you have two GPS units in your car which are telling you different things. My guess is that there is a part of the car or surrounding environment that is blocking the sky view for one of the units, making it less accurate. If your TomTom is more accurate, that's cool, but I bet if you kept using the GPSs, together, you'd find days where the NAH is more accurate. One other thing you have to consider is that the two GPS systems may actually be affecting each other. GPS is nothing more than fancy radio signals. Units on the ground lock onto radio signals by generating their own radio signal, and then comparing it to the signals in the environment until it finds what it's looking for (It's actually called "superhetrodyne" for you electronics geeks). Since there is a radio signal being broadcast by each GPS unit, the OTHER unit in close proximity to it can actually be picked up, and confuse the unit. It doesn't happen often, but it does happen.... Additionally, the designers of the GPS systems have to make judgement calls as to things like "what is an exit?" Sounds like a simple question. But where do you place the "X" that says "exit" in your onboard maps? At the tip of the lane split? At the first curve? Half-way between one highway and another, along the exit ramp? This can be a very difficult decision, since there are so many different kinds of exits, ramps, merges, etc., etc. Obviously, since this is proprietary software, TomTom and the people that make Nissan's GPS make different decisions.... All that being said, I've been particularly underwhelmed with my Nissan's GPS. It has taken us on some sight-seeing trips that got us to a destination nowhere near where we wanted to go. Odd. Very odd. Now, we basically use the GPS on long trips to let us know how much farther it is, miles/time-wise to our destination (Are we therrrrrre yet?!?!)
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Replying to: hiwayman (Jan 15, 2008 9:46 am) http://www.eagerodometers.com/advise.html
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