I am including more details than normal to highlight the path of discovery and diagnosis that others may be on.
VEHICLE: 2017 Highlander Hybrid Limited Platinum
I had been tracking fuel usage and mileage since very beginning (February 2017), including type of fuel used (ethanol vs. not), fuel source, and relative weather conditions (since temps here vary by more than 100 degrees F during the course of a year, with the extremes having a huge adverse impact on fuel economy).
In late 2018, after driving it for about 18 months, it seemed like I wasn't getting as good of fuel economy as initially -- mainly based on the vehicle's dash reading itself. I did some experimenting with 1) avoiding ethanol-blended gas, 2) using ECO mode vs. not, and 3) trying extra hard to improve my fuel economy. Nothing made a difference. By Thanksgiving I was at about 32000 miles, and decided to replace the factory tires with something better suited to a potentially severe winter. I sacrificed the low rolling resistance for better gription = Goodyear Assurance Weatherready. Put the same on our 2013 Ford Fusion Hybrid. No additional / noticeable drop with the more aggressive tires, and my wife said the Fusion did not drop with them either. (she averages in the low- to mid-40's, and tracks very closely)
Earlier this year I finally entered all of my fuel usage data in to a spreadsheet so I could dissect in more detail. I computed the MPG for each fill, plus a rolling 4-tank average to better account for variances. The results were telling: From a consistent 30mpg (mild temps) to 27mpg under similar conditions (25mpg if heavy A/C use, or 22mpg at its coldest). At best it was not far off the EPA ratings (29 city, 27 highway) but definitely below previous performance. Have not approached 30mpg since last August.
Before heading to the mechanic, I did a lot of internet research. I ran a couple of bottles of Chevron Techron, and bumped up the air pressure in my tires a bit. Neither made a difference.
THEN I checked more details about resetting the computer (ECU), as I had read in a few places, in case it was using some inappropriately-remembered settings. Not knowing exactly which fuse did what for this model, I pulled multiple -- from those labeled EDU to EFI to ETCS to ECU-IG. Upon startup I did not notice that any settings were missing or reset, and it ran fine, so I wasn't sure it had reset anything. A half-hour test drive was showing similar MPG readings.
I saved disconnecting the 12V battery for last. I left the NEG terminal off for an hour, then reconnected. (realized later that I didn't try to more fully drain any electrons in the system) Upon startup the engine was still warm and the big batteries well-charged, so the gas engine did not engage right away. After several seconds it finally did, ran perhaps a bit rough for a bit, then smoothed out and shutdown soon after.
I headed out for another test drive, taking it easy. Outside temp around 80, window down, A/C off. I reset the vehicle's gauge upon reaching a flat area. Going 45mph I was getting 33mpg, whereas for the last several months it would probably have been 27mpg. Did some minor hills, stop-and-go, city driving from 35-45mph. End result still around 33mpg.
The next day I headed out for a longer drive. City driving with hills and consistent 40-45mph, followed by flat highway going 50-60mph. I was averaging 35mpg and loving it -- fully convinced that it was better than ever. It did drop after more hills and more frequent stops, then return home totaling 80 miles. Final average was 31.5mpg for that trip. Undoubtedly better than the previous year, but not even a full tank therefore too early to declare victory.
Finally filled up this morning after 9 days of a typical city/highway driving. MPG was 29.5, and that includes about 50 miles (out of 423 since last fill) that took place before the computer reset. The previous 1500 miles had averaged 26.1 mpg. Easy 10-13% improvement.
I will continue to track and monitor. 1000 mile trip next week will provide another good test.
VEHICLE: 2017 Highlander Hybrid Limited Platinum
I had been tracking fuel usage and mileage since very beginning (February 2017), including type of fuel used (ethanol vs. not), fuel source, and relative weather conditions (since temps here vary by more than 100 degrees F during the course of a year, with the extremes having a huge adverse impact on fuel economy).
In late 2018, after driving it for about 18 months, it seemed like I wasn't getting as good of fuel economy as initially -- mainly based on the vehicle's dash reading itself. I did some experimenting with 1) avoiding ethanol-blended gas, 2) using ECO mode vs. not, and 3) trying extra hard to improve my fuel economy. Nothing made a difference. By Thanksgiving I was at about 32000 miles, and decided to replace the factory tires with something better suited to a potentially severe winter. I sacrificed the low rolling resistance for better gription = Goodyear Assurance Weatherready. Put the same on our 2013 Ford Fusion Hybrid. No additional / noticeable drop with the more aggressive tires, and my wife said the Fusion did not drop with them either. (she averages in the low- to mid-40's, and tracks very closely)
Earlier this year I finally entered all of my fuel usage data in to a spreadsheet so I could dissect in more detail. I computed the MPG for each fill, plus a rolling 4-tank average to better account for variances. The results were telling: From a consistent 30mpg (mild temps) to 27mpg under similar conditions (25mpg if heavy A/C use, or 22mpg at its coldest). At best it was not far off the EPA ratings (29 city, 27 highway) but definitely below previous performance. Have not approached 30mpg since last August.
Before heading to the mechanic, I did a lot of internet research. I ran a couple of bottles of Chevron Techron, and bumped up the air pressure in my tires a bit. Neither made a difference.
THEN I checked more details about resetting the computer (ECU), as I had read in a few places, in case it was using some inappropriately-remembered settings. Not knowing exactly which fuse did what for this model, I pulled multiple -- from those labeled EDU to EFI to ETCS to ECU-IG. Upon startup I did not notice that any settings were missing or reset, and it ran fine, so I wasn't sure it had reset anything. A half-hour test drive was showing similar MPG readings.
I saved disconnecting the 12V battery for last. I left the NEG terminal off for an hour, then reconnected. (realized later that I didn't try to more fully drain any electrons in the system) Upon startup the engine was still warm and the big batteries well-charged, so the gas engine did not engage right away. After several seconds it finally did, ran perhaps a bit rough for a bit, then smoothed out and shutdown soon after.
I headed out for another test drive, taking it easy. Outside temp around 80, window down, A/C off. I reset the vehicle's gauge upon reaching a flat area. Going 45mph I was getting 33mpg, whereas for the last several months it would probably have been 27mpg. Did some minor hills, stop-and-go, city driving from 35-45mph. End result still around 33mpg.
The next day I headed out for a longer drive. City driving with hills and consistent 40-45mph, followed by flat highway going 50-60mph. I was averaging 35mpg and loving it -- fully convinced that it was better than ever. It did drop after more hills and more frequent stops, then return home totaling 80 miles. Final average was 31.5mpg for that trip. Undoubtedly better than the previous year, but not even a full tank therefore too early to declare victory.
Finally filled up this morning after 9 days of a typical city/highway driving. MPG was 29.5, and that includes about 50 miles (out of 423 since last fill) that took place before the computer reset. The previous 1500 miles had averaged 26.1 mpg. Easy 10-13% improvement.
I will continue to track and monitor. 1000 mile trip next week will provide another good test.