I get over 30mpg on the highway if it's a mostly highway trip. About 75MPH.

08 GS350 w 56K mi

 

I really want to achieve what MPG's you guys are getting, it honestly makes owning this 3GS that much more worth it! I bought my '08 GS350 RWD back in November 2021 with 93k miles, and the best that I've been able to get is 26.5 on all highway driving (refilled gas right next to freeway entrance, that's probably why) but typically 23-24 highway even if I baby the throttle, but in the city I rarely get over 19.5-20.5 and I really have to drive like a grandpa for that one.

I've tried all the common fixes, like Correct tire pressures, using "SNOW (eco) mode while driving, 3k Oil Change Intervals, fuel additives, but can never really go past these figures, no matter what I do. I think my next step is to carbon clean the engine, like @CowBoE has done on his '06 GS300 and see if it gets any better. If you guys have any other suggestions, I would very much appreciate the input.

Best, Norm

 

To be honest, I use my '08 GS 350 in SNOW mode all the time and usually get better MPG's than compared to not using it or using PWR, as I'm pretty sure PWR mode engages higher rev's all the time and holds the gears until you really push it. I am pretty sure there was another post where they did comparisons and people saw the same results as mine, with some even saying SNOW mode did marginally better for MPG's. I would love to know if anyone has better results using PWR mode though, as that is really interesting.

Best, Norm

 

Try putting more pressure in your tires to see what MPG you get. I think I was running about 36-37. I have about 40lbs in all 4 right now. I will air back down a bit later. I was getting low pressure warnings when the cold hit where I am, so I aired up at Lowes with the intention of letting some out, but haven't yet.

 

My GS350 2008 has had 29 mpg in the summer but not consistent. This winter I have only seen a high of 22 mpg. I have new spark plugs only 3 months old.
Peace.

 

Record is 42 mpg average on a full tank after 500 miles city/highway on my 2013 Lexus ES300h. My overall average is much lower at around 36.5mpg in the past 6 years.