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Huge drop in MPG, down nearly 25%

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12K views 52 replies 20 participants last post by  JasonFH 
#1 ·
Our 2022 Sienna averaged 37/38 MPG until about 7500 miles. We are now at 9500 and averaging 29/30 MPG under the same driving conditions. This has dropped off in the last 2000 miles and I am concerned.

I typically change my own synthetic oil at 5K intervals but Toyota would only cover on 10K intervals for their warranty/ToyotaCare service. Since it is new, I followed their recommendation. Besides oil breakdown, which would seem wild for this dropoff, any other thoughts?

[Apologies if this has been covered previously; I could not find anything on this specific issue but my forum search my have failed (if so, please link).]
 
#2 ·
Low outside temps may be part of the problem. The engine needs to run more and maintain a certain temp so that the computers will all stay nice and toasty. But seriously I would not worry about it. It will bounce back. I have owned many cars,over 40 of them. My last car was a 2021 Sienna LE,before that a 2020 Chevy bolt, before that a 2014 Prius,before that a 2010 Prius V, etc.
Too many short errands or trips can also give you worse mileage it the outside temps are low. Your van's engine must maintain an acceptable temperature in order to utilize the EV side of the van. Batteries work better when warm.
 
#16 ·
Low outside temps may be part of the problem. The engine needs to run more and maintain a certain temp so that the computers will all stay nice and toasty. But seriously I would not worry about it. It will bounce back. I have owned many cars,over 40 of them. My last car was a 2021 Sienna LE,before that a 2020 Chevy bolt, before that a 2014 Prius,before that a 2010 Prius V, etc.
Too many short errands or trips can also give you worse mileage it the outside temps are low. Your van's engine must maintain an acceptable temperature in order to utilize the EV side of the van. Batteries work better when warm.
My 2022 Sienna has 1200 miles on it getting 35 mpg but I noticed when I turn car off on dash shows 48 mpg for a split second before it goes away would that be mpg for just that trip and the other one that I pull up on the steering wheel is an avg ?
 
#7 ·
Our last fillup at end of Nov was about 39mpg in temps below 60f.

Keep monitoring in case cause is something other then what other posts mentioned.

Based on just CPU mpg we're at about 36mpg so far in December but CPU is optimistic so will update after next fillup with manual calculation.
 
#8 ·
yea mine dropped too. I was getting around 38mpg combined until the temperature dipped recently. I think idling also drops the mpg. We sit in the car with the heater on while waiting for kids to finish their activities. So gas is burning but you're not moving.

milesgallonsdollarsmpg
?8.94
318.58.14539.10374463
410.110.49643.0239.07202744
304.88.77532.6334.73504274
423.812.12248.4834.96122752
364.98.86831.0341.14794768
?9.027
388.911.40441.0434.10206945
37412.14843.7230.78696082
 
#9 ·
On top of what's been said already, check individual trip mileage if you don't already.

Turn off the child alert. Once done this, you will see trip mileage after you shut-off car, but before opening any doors. This way, you can see if particular trips and/or drivers are causing most of the low mileages.

FWIW, we get about 29-31 in summer, 25-27 in winter. When I let my friend drive it, he easily gets 38-40 in summer;).
 
#13 ·
Winter gas may have slightly less energy, but most of the gas usage is warming up a cold engine, and primarily air density. Air drag is linearly proportional to air density. Going from 90 °F to 40 °F increases air density by 10%. On highway driving, something like 70% of the power to drive a vehicle may be used to overcome air drag, with the rest being rolling resistance of the tires and drivedrain losses. So even with the same gas, highway MPG from 90 to 40 °F will decrease by something like 7%. So if you can get 40 MPG highway driving at 90 °F, you'd expect a 5 MPG loss just due to the air density increase alone at 40 °F, all other factors being equal. And they aren't, as winter blends may have slightly less energy (not significantly so), and cold engines burn rich as they don't vaporize as much fuel as when they are warm, and lots of people idle engines to warm up their vehicles in the winter, which will further reduce MPG.
 
#14 ·
Snow tires and winter blend gasoline will reduce your mileage. Throw in longer idling times as you wait for the windshield to defrost and you’ll be down at 39 mpg in no time.
 
#18 ·
I wish I could get anywhere near where you guys are getting. We haven't gotten a single tank over 32 mpg since we bought our '22 Platinum AWD. Right now our average according to Fuelly is 31 MPG. It's not the 36-38 we expected when we bought it. It now has 20k miles and has gone on many long road trips, lots of around town. Tried hypermiling it for many tanks with no change. I've always gotten above the estimated fuel mileage in all my vehicles, so I know it's not how I'm driving it.
 
#27 ·
Lots of good advice... think now need to get checked at dealership as temps warm enough in your area to rule out cold, PSI, tires, filters, oil, etc.

Make sure to mention that you were getting mid 30s MPG up to a certain point and then just dropped off. Perhaps a hybrid battery issue. It gets fully charged [perhaps all bars less 1] and gets to 3 bars charged?
 
#28 ·
Our 2022 Sienna averaged 37/38 MPG until about 7500 miles. We are now at 9500 and averaging 29/30 MPG under the same driving conditions. This has dropped off in the last 2000 miles and I am concerned.

I typically change my own synthetic oil at 5K intervals but Toyota would only cover on 10K intervals for their warranty/ToyotaCare service. Since it is new, I followed their recommendation. Besides oil breakdown, which would seem wild for this dropoff, any other thoughts?

[Apologies if this has been covered previously; I could not find anything on this specific issue but my forum search my have failed (if so, please link).]
I have a 2023 sienna XLE. with 5800 miles on it. Never got above 30mpg but have gotten down to 25mpg. When I complained to the dealer, they seemed more interested in buying the vehicle back at a big discount rather then fixing the problem. Right now I don't think these vehicles are capable of producing the rated 36 mpg. It is a sham.
 
#32 ·
On Fuelly, the 20 owners of MY 2023 Sienna report 32.7 mpg on average, with about 1/3 of them clocking 36 mpg and higher. But it's also true that some of them languish below 30 mpg.


The average for MY 2022 is slightly better, while for 2021 it is a little worse. This makes me think that as a species the Gen 4 Sienna is quite capable of delivering the advertised fuel efficiency - with the YMMV disclaimer of course
 
#40 ·
A long time ago, I had a used Dodge Grand Caravan. I bought it in the summer. As part of my pre-trip checkout for a winter trip, the 12v battery had low voltage, in the range of 11.5ish. I connected my charger overnight, but it was still low. My hydrometer showed a dead cell, but the van was still starting without hesitation.

It was a Bosch battery still under warranty, and I had to drive some distance to an authorized Bosch retailer. They tried to brush me off and say that I should put it on a charger overnight. I said I would wait while they put it on their 2 hour charger. Two hours later they gave me a new battery because mine was not charging.

So, in my experience, if a 5 cell 11.5v battery can start a V6, it could also be able to start up the computer on the Sienna. Then, the DC-DC converter will start charging the 12v battery, which would never get up to voltage. The traction battery will be drained quicker than normal due to continuous charge of the 12v battery. This will result in the ICE running more to recharge the traction battery, reducing your fuel mileage.

It is worth a shot to check the 12v battery. It may not be you issue, but it is not a bad thing to check the battery.
 
#52 ·
I posted a couple of months ago about my first full tank as received from the dealer for my 23 Platinum AWD and how excited I was to get to 650 miles after pushing it for about 15 miles with the yellow fuel light on, so very close to empty, save maybe a gallon? Then on my next full tank, which included about 450 miles round trip to a hilly area and a Thule on top, I eked out about 490 miles, again pushing the limit. I also had a full capacity of passengers, so I drove conservatively and barely over the speed limit. But I'm still surprised at the mileage dropoff of at least 10mpg. Not sure if all the hills and regen braking helped much at all. My first tank also involved more city and stop and go driving.
 
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