Sudden and drastic drop in MPG?

[Blitzkrieg]

I assume you are using the computer to calculate MPG?

Take it and fill it up, drive for XX miles and record the mileage via the ODO and then fill it up again and calculate MPG the old fashioned way.

I don't know what the reset totally does behind the scenes but 5 MPG is in left field (and likely not actually reality). And it ain't a different viscosity oil or something crazy like that. ;-)

 

[4RunnerAU]

So far your calculations and distances run are too short to really tell you anything. Without doing some distance you are being a bit paranoid.



1.The mpg gage on the dash is very accurate, in spite of what people on here allude to.



2. Driver normally as you have for those first 10,000 miles for a couple of tanks full.



3. At each fillup reset the mpg gage.



BTW: To get such terrible gas mileage on your truck (both before and after you noticed the change) traffic around Atlanta must be really terrible!



I have very heavy E rated mud terrains (stock size on my truck) and the only time it gets down to 13 - 15 mpg is when I'm in low range on the trail. Around town I typically get 16 - 18 mpg and on the highway at 65 between 19 and 21...... Of course in my neck of the woods (no trees here though) the traffic is very light - even in town.

Yeah. Traffic here sucks. It's frustrating. We are doing our best to get out but wife is due any day now and we want to let the dust settle before we make serious moves to another part of the country.

 

[Foques]

It should only use about 0.5-1 gallons per hour of warmed up idling. Even if they take their time pulling it in, it's hard to believe they would let it idle for more than an hour unless it's a job they can do with the engine running and they want the radio or A/C on or something. I hope they don't do an oil change with the engine running, but I wouldn't put it past some dealerships.

a local dealership idled my truck for about two hours at one point, my mpgs dropped much deeper than that

 

[Ron4RNevada]

4RunnerAU - I just realized you were mentioning that you were wondering about the first few miles after the oil change. The MPG GAGE does act funny for a few miles after the dealer has reset the maintenance reminder. That's normal.

 

[Lester Lugnut]

OP - how do you calculate mpg?

 

[4RunnerAU]

OP - how do you calculate mpg?

Ha - that's the key here. I'll mention how I do it and give an update (if anyone cares).



For how I calculated the difference in MPGs - I used a running total from the computer MPG calc. I had about 3k-5k of 'history' built into the average that I used to compute it. My on-board computer average was 18.4MPG prior to the oil change. All of that mileage history is based on my normal driving habits i.e., it's not that 3k of history included a 1,500 mile road trip. It's 100% normal, routine driving and my routine is consistent every week. Key is that it's very routine. Too routine, IMO. Thus, on a week-to-week basis, I can expect about 18.4MPG (all things being equal). You'll have ups-and-downs for gas quality, days when traffic is better/worse than normal etc. So, that's my basis for "normal" and given that my driving for the week after the oil change was very normal, I think that 18.4 MPG was a reasonable basis for my "normal" MPGs.

To calculate my actual MPGs after the oil change, I used a hand-calculation based on my trip meter (which was reset when I went to the dealer + adding in miles I drove from gas station to dealer) and the fuel consumed. Fuel consumed was originally estimated based on the tank gauge position (horrible method) but was replaced by the 'actual' when I filled up on Sunday evening. My actual MPG was 16.3 MPGs (267 miles driven over 16.4 gallons used). So when compared to my overall average MPGs, it's not quite as dramatic as I had originally estimated (-10% vs. -25%) but still enough that I consider it 'material' and believe something is off.

I also noticed that the running total Avg. MPGs had dropped down to 18.2MPGs in a 6-7 day period despite consistent driving habits. That means that the MPGs that I experienced over my last tank were drastic enough to reduce the average. Hopefully that tells you something. So, I went ahead and reset the MPG last night to get a new 'basis'. I'll take another look at it when I get to about 1k miles or so and see if the average is down considerably. I know people think I'm being paranoid, but I think I'm just very "in-tune" with my vehicle.

I will say that my vehicle just "feels" different from a steering/ride standpoint. I'm not sure what it is, but I'm wondering if the alignment is actually off.

 

[4RunnerAU]

When I reset the display with the button on the steering wheel, the mpg goes to hell for a while for me... recalibrating with the limited sample that it has.

Are you sure this isn't all that happened? It takes a few days to a week for mine to work itself back to familiar territory.

I used to calculate fuel consumption with gas receipts before, but I found the 4runner to show a very similar number on the display. Resetting it always makes it dip low for a short while.

I didn't reset the MPG meter but the TRIP meter. So, my MPG meter was still 18.4MPG when I picked it up but the Trip A meter was 0.0 miles. Sorry for confusion. The MPG meter had a running "history" of about 3k-5k miles on it and since my driving is very consistent from week-to-week, the computer average MPG was a good basis to use as an MPG I would see on a weekly basis, especially since my driving habits didn't change after the oil change.

So basically, I drove "normal" for 3k-5k miles and I observed 18.4MPG. After oil change, I drove "normal" and would have expected 18.4MPG but instead experienced 16.4MPGs, which I based on my hand-calculations for that last tank of gas. I calc'ed that using the distance I drove per the trip meter + distance from gas station to dealership (because I would have used gas to drive over to the dealership and the distance I drove would not have been included in the trip meter) over the number of gallons I used to refill.


All of this for me to wonder what could have caused a 10% drop in my MPGs . People have mentioned winter-blend fuel, but I have never noticed a drastic drop - i've read that the drop is typically slight (i.e., 1.7% per an article I just read) and I would be surprised if the blend of gas used down in the South is equivalent to those used in the North, given our drastically higher average temperatures in the fall and winter.

 

[darrylj]

Just use the instant mpg gauge and set it to zero after you have gotten to 70 mph.

It's my recollection (and I could be wrong) that when you reset the gauge when parked, it starts from 0 but when you reset it while moving then the last recorded total is kept and used as part of the new calculations.

 

[Ezlife45]

Did the dealer readjust your tire pressures?

 

[4RunnerAU]

It's my recollection (and I could be wrong) that when you reset the gauge when parked, it starts from 0 but when you reset it while moving then the last recorded total is kept and used as part of the new calculations.

Huh. Interesting. Well, I definitely reset mine on Monday night while moving.

 

[4RunnerAU]

Did the dealer readjust your tire pressures?

I'm thinking no - I keep mine around 38-40psi. They were at 36psi, but I'm thinking colder weather had something to do with that (air contracts in cold, expands in heat, right?).

 

[4RunnerAU]

Anyways - here's an update....

I did some googling and I read that quite a few people have experienced similar issues. I guess a common thread is that dealers can overfill the oil and that can cause MPG issues. Either way, I checked the oil and the level seemed fine. The color was brownish tint. it didn't look incredibly clean since I've only driven 400ish miles since the oil change but I'll check again and google.

The steering/alignment does seem a little off/quirky - just doesn't feel as tight as it was before i hit that curb. I'll get it checked out. I can't stand it when my vehicle feels out of alignment.

 

[philsey]

It's my recollection (and I could be wrong) that when you reset the gauge when parked, it starts from 0 but when you reset it while moving then the last recorded total is kept and used as part of the new calculations.

Don't think so. I'll often reset mine when I hit the highway. Typically, I avg 18-19 mpg overall, which is >80% city.

If I'm driving 65, the mpg display goes right to ~45 mpg, and then settles/stays at ~23-24 mpg within ~30 sec. This would not be the case if the previous reading of 18-19 were averaged in.

 

[4RunnerAU]

UPDATE: 12/8/2015

It's been a little hectic since I last posted since my son was born on Nov. 15th (whoo! look-at-me-post) but I've been tracking my MPGs. I decided against getting the alignment checked (plus i just ran out of time).

I decided to reset the gauge again, but since I took off work after my son was born, it's only been capturing the short trips around town. My MPGs dropped substantially to less than 17MPGs (which, to some degree, is to be expected).

I have noticed that the MPGs seem to have been in a constant free-fall. At first I thought it was from the trips around town but I noticed today that my MPGs dropped by 0.2 from 16.8 to 16.6 after a 10 mile trip on the freeway today at 70mph, which is what makes me think something's up.

 

[Jetboy]

I've noticed somewhat the same thing in my '15 TEP. I can point to the exact time it changed for me. Going over Malad Summit - not a particularly high pass, but a 5ish minute sustained 3rd gear pull at 85mph (5000rpms) and it's never returned good mileage after that. The rest of that trip including two more tanks I got less than 16mpg.

This feels very much like an o2 sensor failure to me. Just like the 3rd gens where the o2 sensor would fail, but not enough to trip a code, and you'd lose 3-4mpg. It's very common on the 5vz engines. So much so that it's just standard maintenance to replace the sensor every 50k miles. I hope that's not the case with the 5th gen. I'm curious if a sustained near WOT for a few minutes would cause this.

I'm going to put a few more tanks through before I make a final call on investigating further, but at this point it looks to me like there may be a problem.

 

[4RunnerAU]

I've noticed somewhat the same thing in my '15 TEP. I can point to the exact time it changed for me. Going over Malad Summit - not a particularly high pass, but a 5ish minute sustained 3rd gear pull at 85mph (5000rpms) and it's never returned good mileage after that. The rest of that trip including two more tanks I got less than 16mpg.

This feels very much like an o2 sensor failure to me. Just like the 3rd gens where the o2 sensor would fail, but not enough to trip a code, and you'd lose 3-4mpg. It's very common on the 5vz engines. So much so that it's just standard maintenance to replace the sensor every 50k miles. I hope that's not the case with the 5th gen. I'm curious if a sustained near WOT for a few minutes would cause this.

I'm going to put a few more tanks through before I make a final call on investigating further, but at this point it looks to me like there may be a problem.

Very interesting. I'm not a mechanic but that sounds plausible. I don't have a specific moment which caused my decline from a driving perspective, just that it seemed caused by a trip to the dealer.

 

[4RunnerAU]

Update - 12/21...I went and got my alignment checked. The guys at the counter laughed at me and said I was being paranoid. Oh well - I can tell something feels off in the steering wheel. Everything looked normal except for caster on my front right tire. While that was in spec, it was about 0.2 degrees from being out of spec (range was 2.5-4.5, mine was 2.7 - left wheel was 3.2 degrees - right in middle of the range). That probably explains the steering feeling funny.

As for the MPG issue, I am at a loss. Since my son was born, I have only been driving short errands. It has bottomed out at 13.9MPG at some points. It's too hard to tell right now but I will know more when I go back to work and my "normal" driving habits resume.

Will keep updated. I will say that given my bad mileage, I am tempted to get some bilsteins since I avoided earlier to max out my MPG (more of a challenge than a practicality thing) and replace the Hankooks with 275 Duratracs.

 

[Diesel_Dog]

Since my son was born, I have only been driving short errands.

This is likely the culprit of the poor MPG.

 

[BlackWorksInc]

Update - 12/21...I went and got my alignment checked. The guys at the counter laughed at me and said I was being paranoid. Oh well - I can tell something feels off in the steering wheel. Everything looked normal except for caster on my front right tire. While that was in spec, it was about 0.2 degrees from being out of spec (range was 2.5-4.5, mine was 2.7 - left wheel was 3.2 degrees - right in middle of the range). That probably explains the steering feeling funny.

As for the MPG issue, I am at a loss. Since my son was born, I have only been driving short errands. It has bottomed out at 13.9MPG at some points. It's too hard to tell right now but I will know more when I go back to work and my "normal" driving habits resume.

Will keep updated. I will say that given my bad mileage, I am tempted to get some bilsteins since I avoided earlier to max out my MPG (more of a challenge than a practicality thing) and replace the Hankooks with 275 Duratracs.

Toyota usually calls for at most about .2 cross caster difference; it could be the culprit but I mentioned in an alignment thread that you can really only align a vehicle to flat roads because crowns and road angle vary greatly so trying to adjust for them is difficult. I noticed in my 4th gen that while my numbers are dialed in exactly the same, the severe crowns/angles in the mountains and in some of the roads in my area cause my vehicle to pull more than others.

 

[4RunnerAU]

This is likely the culprit of the poor MPG.

Yeah - like I said, we won't know till my driving habits go back to normal. It was dropping before my son was born, though, hence why I started the thread.