3 weeks ago I got my oil changed at the place by my house. Same place I always go. My 09 has been in there 3 times before to get the oil changed. I noticed that I had gone from 19.5 on the highway to 17.5. I was a little puzzled. Then yesterday on my way to Lubbock for a meeting, it popped up that I only had 5% oil life left. Kind of strange considering that it had only been 2K miles since my last oil change. So today in Lubbock I got my oil changed prior to driving home. I got 19.8 MPG on the return drive (about 360 miles). This really peaked my curiousity. I went back and looked at the receipt that they gave me at my previous oil change and noticed that they had put 5W30 in it instead of 5W20. Could this really account for such a drastic change in MPG and the accelerated decline in oil life? I am a nut about only buying gas at Shell if possible, so I can't attribute it to buying cheap gas at RaceTrac or Walmart. Any thoughts you guys have?

 

did they reset the oil life i dont think they did as far as the mpg maybe you had head wind but if got the same mpg with the 5w20 i would say it did make a difference i always use 5w20 and get adout the same mpg as yourself.

 

The oil life monitor is only looking at a combination of miles and adding in factors like throttle position and maybe a couple others. It's not actually measuring anything in the oil. In other words, it's just a fancy version of the static cling oil change reminder sticker. Ignore it.

Tank to tank variations in fuel mileage can sometimes be as much as you've seen. A small peice of that might be due to the difference in oil viscosity, but only a very small percentage. I've been logging fuel mileage/useage for at least the past 10 years. Temperature changes seem to be one of the bigger factors in variation. That's outside of things like differences in the weight of the load you may be carrying.

The short of this, is I wouldn't worry about it. Be sure to remind your shop doing the oil change. Use 5W-20 ONLY. Tight tolerances in these motors really require this thin oil.

 

Could be a couple things... colder weather has finally gotten here to Texas, that zaps MPG. Are you driving in windier conditions than before? With the recent cold fronts that could be it... it could also be that you filled up with E10 somewhere. That seems to ZAP my 09's MPG. I did see a very slight drop in MPG when I used 5w-30 once in my 2008 F, but it was maybe .5 MPG.

 

JJ;

I would bet that that change was due to tire pressure change by the oil shop. Did they set all the tires a bit low?? If you run our big tires softer, the MPG changes, and that is about the right amount of MPG change for a pressure change. Even if they did not intend to, the accuracy (or lack of it) of some shop gauges could account for enough pressure difference to change the MPG you get.

This issue is why I started to check my own tire pressure on a weekly basis, with my own tire filler off my own air system in my shop. The oil change side of my dealer consistently sets them too low for my liking, even when I ask them not to.

Just my .02

BJ

 

It can make a diff but if u really want to get the best mileage drive 60 mph or less and then reset the mileage calculator and then go 70 or 75 and watch the difference. The computer on mine that calculates the mileage is off about 4/10's of a mile off but pretty close. Of course there are many other factors but an instant one is to drive 60 or less if you can.

 

Anyone know of good miliage logging software (free). I am curious to see how much the cold weather does really effect my trucks MPG. We've been getting upwards to -20 degree C here the last week and in combo with my studded winter tires my truck seems wicked hard on fuel right now.

 

There are a few out there - I like:

fueleconomy.gov

On the front page, click on "Your MPG" at the lower left.

Once you set up your account, you can enter your fill-ups, and then track your MPG and compare it to others.

 

For the monitor, I would assume they did not reset it. the 30wt oil will take a little more MPG. Discount gas along with winter blend could also account for some MPG loss.

 

Every time I get the oil changed, I check that the monitor is reset. So I know that it was reset. I am pretty much a weirdo when it comes to things like that.