I've got a problem here that is driving me nuts and I hope you can help. First, let me note that I've searched the forums but not found an answer to my satisfaction, so I apologize in advance for another MPG related thread.
My wife and I bought a brand new Pro-4X with 200 miles on it on Sept. 1, 2012 as I wanted one of the last Nashville produced models before they moved production to Georgia (funnily enough, I also just moved to Nashville from Delware in January). I immediately installed a flat KN drop in filter and swapped the factory tires for Cooper ST MAXXs of the same size. These are my only mods as of yet.
Once we got it over the break in period (i.e., 2000 miles), I was hitting 16.5 in town, and 19.8(!) on the interstate at 70 mph with cruise on. I was a super happy camper.
We hit about 4,000 miles on the odometer around Halloween 2012, which was also when the temperature in Delaware dropped to cold as heck, and, I assumed, the winter gas blends kicked in. I also got my first oil change then.
In early November 2012, when I started using the heater for the first time, I noticed the sound of "drops" hitting the factory skid plate. The car had never had ANY leak of any kind before (that I could hear). I figured this was due to the compressor being on and generating some condensation. Regardless, the truck still emits some of these drops now, whether or not the heater is or has been on. I have looked underneath, and none of the drops appear to be anything other than water.
Also in early November 2012, I noticed a terrible drop in gas mileage. I went down to 16.5 on the interstate (70 mph with cruise on) and about 12.2 in town. I have not changed my driving habits, am not a lead foot, and generally am cognizant of my RPMs. In sum, I'm the guy who pays careful attention to my enginge performance and driving style.
Last, although I'm not sure because I've never owned an Xterra before, I think the truck started shifting too much/easily at city speeds (e.g., from start to about 40 mph) at some point close to the mileage drop. Compared to the 1996 Explorer I was previosuly driving, the Xterra seems to shift up and down WAY TOO MUCH on relatively flat city roads, especially around 30-40 mph.
Has anyone else experienced this weird drop in MPGs? I had read a lot of positive reviews on modern Xterra fuel efficiency, but am baffled and concerned by this development. I thought it could be winter gas, cold weather, underinflated tires (I'm always at 50 psi on the MaXXs), but surely none of these is the reason for my loss of 3MPG!
I know these trucks are gas guzzlers compared to hybrids, and I'm ok with that. However, the sudden loss of 3MPG for no reason worries me, and is too much of a drop for me to just let it go.
Besides, I want to get a Shrockworks front and rear bumper installed. These 3 MPGs were the ones I was saving to sacrifice to the Shrock!
3MPG loss at 4000 miles, and a strange drip hitting the skid that appears to just be water even though you're not running the AC.
My first concern with that drip is the radiator which is right there. I'd be worried that there might be a problem with a hose and that it's loosing water slowly. But being as new as it is I'm sure it'd be filled with coolant and not water, so condensation is more likely, but the heater shouldn't create condensation and you're definitely not running the AC at this time of year... chances are it's completely unrelated to the MPG drop though if you're not seeing anything over heating.
Winter gas can definitely hit fuel economy hard, and you also say you just moved... to Nashville from Delaware... Delaware is much closer to sea level than Nashville but I wouldn't imagine it'd be a terrible change... 60ft vs 500ft, nope that shouldn't be too significant.
OK a couple of variables to get out of the way:
First, what kind of oil was changed into the Xterra, was it a good brand and was it the proper weight.
Second, what kind of fuel is it getting? Did you start using a different brand, different grade?
Third, have you checked the airfilter and made sure nothing's clogging it up? If an engine can't breathe it'll use more gas for sure.
Fourth... I haven't quite come up with a fourth yet but I'm working on it...
The transmission issue with the constant shifting would seem to indicate that the X is working harder than it should be to put down the same force (or at least thinks it needs to work harder). This can be caused by weight or friction... bad oil or the wrong weighted oil can do that inside the engine, the ebrake stuck in the engaged position can add that kind of friction too.
Thanks REVU. Here are the answers to your questions, going backwards:
Fourth. The KN is an oiled filter. But I noticed the drop some thousand or more miles after putting it in.
Third. amazingly, the air filter is completely clean. Visually the KN looks like it did out of the box. Clean it anyway? Still nice and oily.
Second. I have generally used regular unleaded from a variety of stations in Delware and Penn. I had hoped the crappy mileage was indicative of DE's bad winter gas, but being back in NAshville hasn't seemed to affect it at all. Still crap mileage. I tried a few tanks of premium over the course of a 1000 mile trip in December, and that boosted my MPG some, but not enough to justify switching to that gas.
First. I do not know about the oil, as I took it to the local Nissan dealer in Wilmington DE. I assumed they put in the right stuff. Mistake?
Generally, the weight issue shouldnt be a problem as it is empty and I already have a baseline from the increased weight of the cooper tires since I never drove it without them. I have checked the e-brake in the past and am sure it is not on or partially engaged (based on me making sure the pull bar is down from the inside of the truck - I wouldn't know how to look underneath to see if it was still engaged).
I also am sure the tires are wearing very well as I haven't lost any measurable tread in 8000 miles. (E load tires YAY!)
Any other thoughts?
Thanks for the response!
No lights are coming on at all, and the car seems like it is running as it should.
One would imagine the dealership knows what oil to put in, but I've seen dealership techs screw stuff up before. I believe the accepted oil weight viscosity range for the VQ40 is 5w-30, 10w-30, and 10w-40. I usually use synthetic 10w-30 in my X and it's done really well with that. If it's getting really cold where you are you could try the 5w-30 that holds viscosity better under colder conditions. If the temperatures aren't too cold then you might try the 10w-40 and see if it makes any difference on the hotter end.
It sounds like your air filter is really new so it would be odd for that to be the problem then. And if it was over oiled sometimes the excess oil can get on the MAF sensor and cause weird things to happen. Normally that will trip a check engine light though. And being that you changed it after you were already experiencing issues probably removes that from the equation.
As you have been fueling at an array of different fuel marks, you might try running a fuel system cleaner through your tank - people would probably say something like seafoam or Magic Fuel, I haven't used those so you'd want to read up on them or ask around someone who has. There are also lots of generic fuel system cleaners available through autozone and such, but people around here generally say to go with particular brands that are known to work well. (And not all gas is equal, around here I've seen Circle K gas gunk up engines pretty good because of cheap chemicals and containers that they keep it in.)
The constant transmission shifting is still making me think it's a frictional issue. Somewhere it's working harder than it should be for some reason, and that can definitely cause it to run inefficiently. When it shifts does it shift fast or is there a lag between gear catches?
I will try a new oil change using your recommendations this weekend as its time for another now.
I have not oil the KN; I just dropped it in right out of the box, and havent reoil yet, since it looks clean. Perhaps I should try the old stock filter and see what happens. Is there a way to find the MAF sensor to see if it is gunked up? Would I even be able to tell?
I will try a fuel treatment at my next fill up and see what happens. I will report back on here after that.
As far as shifting, I think it shifts too easily. It doesnt lag or catch as if the tranny is going out (sadly, I've had that happen in my other older trucks over the years). I have been wondering if all xterras shift this easy, as it seems like it shifts into higher gears when it should just stay in the same lower gear given the speed, terrain and city driving. I wonder if I can get a power chip of some sort that will make it stop shifting so easily and stick in a gear longer...
Thanks again for the input! Will take all I can get. This truck is my baby and I plan to do some mods once I get this sorted out.
Definitely! I bet once it's sorted it'll be golden for a long time.
As far as the MAF goes it can be really hard to tell if oil has gotten on it or anything like that. There are MAF cleaners on the market, but it's almost better to stay away from those because if it's not done just right it's really easy to break the sensor and then need a completely new one. So it's risky especially when it's not throwing any code.
Switching into higher gears? That it will do, like if you're cruising at 30MPH and doing fine in 4th gear but it wants to go into 5th gear and so on. Turning off Overdrive using the little button on the gear shifter will help with that some, you just have to remember to turn it back on when entering the highway.
Do let us know what happens after the oil change and fuel treatment though.
Update: Since my last post, I've been drying in town with Overdrive OFF, switching it on only when I hop on an interstate. This seems to have recovered about 1-1.5 MPG and makes the truck shift less on slightly hilly roads at 30-40MPH. I also noticed with OD off that my idle goes down about 100 RPM.
Last night I did an oil change at 8800 miles, putting in the best synthetic the Jiffy Lube guys had. I also added a bottle of fuel treatment picked up from an autozone. I took out the K&N for a good wash and replaced it with the original (and still brand new/clean) paper air filter.
The K&N looked perfectly clean and well oiled just like it did out of the box, even though it hasn't been cleaned in 8000 miles. No particles I could see actually came out during the washing (which I did with the proper KN kit liquids). I have driven through some TERRIBLE salt and snow storms this winter, but could not see or feel any salt grit coming out of the filter. Its drying now and I will lightly re-oil and reinstall later today or tomorrow so as not to skew my results by altering too many variables at once.
Also, I've been paying attention to the locatio nand speed of the drip, though i can't get under to see it again yet. I hear drips hitting the skid plate closer to the middle of the truck (I'd say approximately under the driver's area rather than the engine bay). These still occur in dry conditions and whether or not I turn on any accessories like the heater or AC. The truck did not drip for the first couple thousand miles so I wonder if perhaps some hose could have come loose and I'm loosing power/something out of a bad seal that affects my MPG.
Will update again after putting this treated tank of gas through it.
Tracing down a problem can be one of the hardest things to do especially when it's not causing a major impact on the performance of the vehicle. Just that whole process of elimination thing. Glad you've got some progress there with the OD, I'm a little confused by the idle speed, but we won't worry about that.
Once it's had a chance to eat through some treated gas I'll be really curious as to how it performs. Thanks for the update
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