06 m45 gas mileage

[tigerclaws1318]

does anyone average about 12-13mpg city driving in their m45 cause i do. even in mix highway and city driving i barely can reach 15mpg. im not aggresive on the gas pedal at all. i had only owned the car for a little over a month and i find myself at the gas station very often lol. i changed the oil and run mobil 1 5w30 extended peformance oil with a mobil 1 oil filter. tires are inflated to 33psi cold. im wondering why im averaging so little when the cars stickers said city mpg is 16. the car only has 25k miles on it.

[striz923]

check the air filter maybe??

[tigerclaws1318]

air filter is clean but about to change it to a k&n filter lol

[Q45tech]

The ring tension in new VK45 is low the last thing you need is more dirt from a non oem filter to speed up their wear.

The problem is your version of CITY doesn't comply with the EPA Test version of a rural city................you probably accelerate too fast.

"City: The test is started with the car's engine cold. The car then is operated in such a way as to replicate 11 miles of stop-and-go rush-hour traffic. Periods of idling are included in the test; average speed is 20 mph and top speed is 56 mph.Highway: This test represents 10 miles of a mixture of rural and interstate highway driving. The engine is warmed up before the test begins and the average test speed of about 48 mph is maintained. The top speed reached is 60 mph. No intermediate stops or idling are included in the test.

The EPA acknowledges that test results might differ from real-world fuel economy ratings. It prescribes the difference to — among other things — the fact that the test cars are in optimal mechanical condition and thus perform better. But by looking at the EPA's testing procedure, it is clear that the habits of today's drivers are not duplicated. On most highways, speeds of well over 60 mph are common resulting in much lower fuel economy

[Q45tech]

In theory the newer M should get the same MPG as the old Q45 [90-96] based on engine displacement and weight. However the rear diff and transmission ratios were increased to improve acceleration and magazine test performance. This results in higher engine rpm for the same speed*, which consumes more fuel.

* 90-96 Q45 was 333 rpm per 10 mph in top gear or 2,000 rpm at 60 mph.2275 rpm at 60 mph for 2006 M45 [3.35 x 0.83= 2.78 x tires] vs 0.694 x 3.538 = 2.45 x tires] ...................2.78/2.45= 13.5%

This 13.5% higher rpm at cruise plus the 3.3% decline in heat value from E10 gasoline easily causes a 10% worse fuel comsumption compare to old Q using conventional [non oxigenated] gasoline.

Higher friction from wider than 215/65/15 tires [90-96 Q] made things worse.

All in all I would expect the newer M to consume 10-15% more fuel for the identical driving cycle compared to my 18 year old Q which was optimized for economy based on a 4.5 displacement and 4,000 pound body weight.

[saeedakobiakov]

i would perform full decarb service at the dealler. $150 or so. recommended every 30k.you will get better mpg for sure.you never know what kind of gas previous owner ran.

[tigerclaws1318]

dont know what kind of gas the preivous owner ran. the car only has 25k miles on it. lol