Sudden and drastic drop in MPG?

[4RunnerAU]

So - last Friday I went in and got my 10,000 oil change done on my 2015 SR5. Prior to the oil change, I was averaging about 18.3 MPG. Afterwards, it has dropped to about 13.8MPG (25% drop) with my driving habits/city-highway mix staying the same. This is pretty drastic, so I'm a bit concerned.

I did hit a very low curb at low speed (20mph) the night after the oil change, but my alignment seems fine - the steering wheel doesn't vibrate at high speeds and when I let go of the wheel on a flat surface, it drives in a straight line (it doesn't drift) for quite a bit (4-5 seconds). I just don't seem to think that's an issue - Atlanta has so many potholes and I've definitely hit quite a few deep potholes much harder than I hit that curb and never had a problem. The 4Runner seems like a tank in the wheel alignment regard. I will check tire pressure, but it seems fine. I'll get it checked, but I just wouldn't think an unnoticeable alignment issue would cause a 25% drop in MPGs.

So, that leaves us with the oil change. Given the horror stories on here about dealership oil changes and the fact that the oil change seems to be the watershed event in which my MPGs started decreasing, it seems plausible to consider whether the dealer could have messed up. What are things the dealer could have messed up during the oil change that I should check for?

Any other things to consider? Just remember that the drop was very drastic (which I confirmed via hand-calculations).

 

[Jetboy]

Possibly they filled with the wrong oil? rotax in there would probably do it. But since Toyota doesn't have a diesel...

 

[Land_Shark]

I don't believe winter fuel would account for a 25% drop, but I know it'll be mentioned, so....maybe b/c of the switch to winter fuel at the pumps? I thought that accounted for about 10-15% at the most though.....this is a tough one...

Did you take a look underneath? Did they secure all the skids and plastic correctly? I ask b/c I've found that aerodynamics affect fuel economy far more than weight does at cruising speeds. My lift, tires, front and rear shrockworks bumpers and winch took me down to about 18.5 - 19 mpg, then my bajarack took another 1.5 away.

 

[1engineer]

So - last Friday I went in and got my 10,000 oil change done on my 2015 SR5. Prior to the oil change, I was averaging about 18.3 MPG. Afterwards, it has dropped to about 13.8MPG (25% drop) with my driving habits/city-highway mix staying the same. This is pretty drastic, so I'm a bit concerned.

I did hit a very low curb at low speed (20mph) the night after the oil change, but my alignment seems fine - the steering wheel doesn't vibrate at high speeds and when I let go of the wheel on a flat surface, it drives in a straight line (it doesn't drift) for quite a bit (4-5 seconds). I just don't seem to think that's an issue - Atlanta has so many potholes and I've definitely hit quite a few deep potholes much harder than I hit that curb and never had a problem. The 4Runner seems like a tank in the wheel alignment regard. I will check tire pressure, but it seems fine. I'll get it checked, but I just wouldn't think an unnoticeable alignment issue would cause a 25% drop in MPGs.

So, that leaves us with the oil change. Given the horror stories on here about dealership oil changes and the fact that the oil change seems to be the watershed event in which my MPGs started decreasing, it seems plausible to consider whether the dealer could have messed up. What are things the dealer could have messed up during the oil change that I should check for?

Any other things to consider? Just remember that the drop was very drastic (which I confirmed via hand-calculations).

Distance you have driven it since the change?

Simple test: Take it out on the interstate during light traffic, get it up to 70 mph, reset your instant mpg counter to zero and maintain 70 mph for about a 10 mile loop. On level ground you should see it average around 20 mpg for that interval. If you are watching it even one level mile at 70 mph (no cruise) should see 20+ mpg for a stock 4Runner. If it is only 15 or so then there is a problem. 18+ you are fine and just paranoid. Simple test. Do it and report back.

 

[invisible4Runner]

You could jack it up and see if there is a difference in rotating resistance between your wheels. A seized brake would do the trick, or anything else that is causing extra friction

 

[nb rob]

check that dipstick!

 

[4RunnerAU]

Distance you have driven it since the change?

Fortunately, the dealership reset my trip meter to 0 during the oil change and I had filled up with gas immediately prior to heading over to the dealership, so when I factor in the google maps distance from the gas station to the dealership (10 miles) plus my trip meter (207 miles), that gets me to 217 miles. My gas gauge is at the 1/4th tank line. IME, that usually is about 15-16 gallons when I refill (which is funny since the tank capacity is 23 gallons).

Simple test: Take it out on the interstate during light traffic, get it up to 70 mph, reset your instant mpg counter to zero and maintain 70 mph for about a 10 mile loop. On level ground you should see it average around 20 mpg for that interval. If you are watching it even one level mile at 70 mph (no cruise) should see 20+ mpg for a stock 4Runner. If it is only 15 or so then there is a problem. 18+ you are fine and just paranoid. Simple test. Do it and report back.

Well, I'm not necessarily stock - I have hankook dynapro ATMs in stock size (265/70/17). Either way, I know what my highway MPG is (20.5MPG). I may do hand-calcs instead - I'll fill up my tank, reset the trip meter, get on the highway (all flat) and drive at 70mph for about 10miles (or until I get to the next gas station), refill and divide the number of miles i drove per the trip meter by the number of gallons I had to replace.

 

[4RunnerAU]

check that dipstick!

That's what I'll do at lunch today. How can I check the filter?

 

[1engineer]

Fortunately, the dealership reset my trip meter to 0 during the oil change and I had filled up with gas immediately prior to heading over to the dealership, so when I factor in the google maps distance from the gas station to the dealership (10 miles) plus my trip meter (207 miles), that gets me to 217 miles. My gas gauge is at the 1/4th tank line. IME, that usually is about 15-16 gallons when I refill (which is funny since the tank capacity is 23 gallons).



Well, I'm not necessarily stock - I have hankook dynapro ATMs in stock size (265/70/17). Either way, I know what my highway MPG is (20.5MPG). I may do hand-calcs instead - I'll fill up my tank, reset the trip meter, get on the highway (all flat) and drive at 70mph for about 10miles (or until I get to the next gas station), refill and divide the number of miles i drove per the trip meter by the number of gallons I had to replace.

Hand calculations won't be good for that short of distance because of fuel shutoff, etc. That technique must be used over several tankfuls to get a good number. Just use the instant mpg gauge and set it to zero after you have gotten to 70 mph. That will quickly show you whether you have a real problem. If you can go a few level miles around 20 mpg then there is nothing that is messed up.

Winter gas will cause a drop of around 10% efficiency on average.

Also the oil on the dipstick should be almost clear and pretty thin.

 

[B...]

It might be something as simple as the dealership moving your truck out of the service bay entrance, putting it in line for the oil change, and never turning it off (letting it idle at 0 mpg for who knows how long). I'd do everything else already suggested and watch it for a tank or two before getting too concerned.

 

[ST1FLER]

pull neg cable reattach recheck:flipoff:

 

[Hellamatic]

Maybe a bad tank of gas. Try filling up somewhere different for your next tank if you haven't tried that already.

 

[Land_Shark]

It might be something as simple as the dealership moving your truck out of the service bay entrance, putting it in line for the oil change, and never turning it off (letting it idle at 0 mpg for who knows how long). I'd do everything else already suggested and watch it for a tank or two before getting too concerned.

I recently took mine in for a seal replacement - they definitely did this and my mpgs were down big time.

 

[gingervitis]

Just curious, what dealership did it?

 

[4RunnerAU]

Just curious, what dealership did it?

Nalley Roswell.

 

[m85476585]

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.

 

[4RunnerAU]

It might be something as simple as the dealership moving your truck out of the service bay entrance, putting it in line for the oil change, and never turning it off (letting it idle at 0 mpg for who knows how long). I'd do everything else already suggested and watch it for a tank or two before getting too concerned.

HA I never thought about that.

 

[Ron4RNevada]

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.

 

[nb rob]

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.

 

[Ron4RNevada]

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.

When cold starting after a fill up and resetting the gage the engine is running in the open loop mode until the catalytic converters have warmed up. Takes about 10 miles on a very cold engine. Also the gage isn't "recalibrating" it's simply averaging mpg over a very short amount of miles.

Once a few dozen miles have elapsed you are averaging miles onto a longer data base.

Example: If I fill up on a cold morning, say 20 degrees outside, I'll only have averaged about 14mpg after 5 miles; then I hit 19 after 10 miles; then she's up to 20 in 20 miles. For the rest of the day on a relatively flat highway at 65 mph I'll be seeing a fairly steady 22 to 23 mpg.

The second morning on the same tank it will drop down to about 20mpg until I've done about 10 miles and then it will be back up to 23. All this goes to hell if I start climbing grades; run into a headwind (or side-wind) or hit traffic.