I picked up my G35 a month or two ago and it has 126k on it now. But I am getting terrible MPG 15 to be exact with some interstate thrown in there. I have new Sumitomo 18' tires got tranny oil and engine oil done. I had 18 then I put Lucas Oil fuel system cleaner in the gas tank and it dropped to 15 on the last 3 tanks. I always use premium gas, and that's with me going 45 on city and 60 interstate. Only gets above 3000 RPMs maybe 5 percent of the time. Tips?

 

With that kinda mileage have you had the plugs changed? Should have been done at 100K miles! How about your air cleaner filament, if that isn't clean you'll use more gas due to the lack of incoming air? Tire pressure should be 35, I run 37 but that doesn't help me either!
Gary

 

At that milage it could be O2 sensors, spark plugs, air filter, or the MAF sensor may need cleaned.

 

usually when people talk about "TANKS" they have no clue how to calculate gas mileage. our cars have terrible readings as far as actual guage reading goes...try calculating the correct way. fill tank, note mileage, drive 60 mileas or more, FILL TANK AGAIN and divide gallons used into the mileS DRIVEN ...my car always gets 27.4 (tnpk) on a 6 speed 03 coupe.(63000 miles) bestcar I have ever bought.
THE EQuation could look something like this (2.2 divided into 60)

 

To be even more accurate you should fill up at the SAME station at the SAME pump as well. While there are laws and organizations that regulate units of measure, some can still be slightly off from others for one reason or another.

 

Yup. That gets overlooked.

Different pump nozzles can also shut off the flow at different times too. In order to be accurate, you should use the SAME gas pump when calculating MPG.


OP. What sort of driving are you doing? City or highway? If mostly city, i hate to say it but that's pretty much right on. These cars are terrible in the city, and only marginal on the highway. 15-18 is what I see with city driving, and i can squeak out 24-25MPG on long highway drives, but the minute i hit city roads, the MPG drops like a rock

 

I've averaged just over 21mpg over the last 10+ years. Normally around 17mpg in city, 23-25 highway.

 

He didn't mention throwing any error codes so I doubt any of the sensors are bad or causing poor gas mileage...Gary

 

No codes, I got the diagnostic work done because a had a bad sensor making the call stall when driving. But that was the only thing wrong with it. I suppose I will just be happy that I have a nice car and deal with the crappy MPG. It could always be worse right?? Haha

 

I'd change the air filter for sure, and run some Seafoam through the gas tank. Might not hurt to do a Seafoam cleaning in the intake. I just did mine, used the Seafoam spray into the brake line booster/vacuum line. Smoked up the neighborhood pretty good, but felt an immediate response and power increase. There is a video on youtube on how to do it, pretty easy.

Probably wouldn't hurt to change the plugs, clean the MAF, and check the tire pressure. I run 37 psi, just to get a tad less rolling resistance.

 

The photo below shows my recent round trip from New Jersey to Florida.
The reduced mileage in the center is of local and short distance driving while in Florida.
The four tankfuls prior and the four tankfuls after the lower mileage are all on I 95 using different gas pumps along the way. All 87 octane.

Best mileage calculated on a single tankful was between Ashland, Va and NJ. 300 miles and 10.529 gallons to fill up for 28.49 MPG



Telcoman

 

Why are you using 87 octane? To save $62/yr?

 

I usually put premium I noticed that I waste more gas when I use 87

 

So any tips on getting that mpg besides running regular gas?
And is that photo of an in car computer, and what program is it?

 

28 mpg is crazy high even for highway driving...I'd like to know the secret as well