according to the dash, i average at 19.2 MPG. I fill up weekly with roughly 300 miles on the clock each time, so i figure thats about right. combined city/highway

 

I drove from Atlanta to Athens, AL, about 243 miles. I got 19.8 after my tune with my A/C on the whole time, I didnt think that was bad... Mods in signature.

 

I get 19 mpg mixed with ac on always and a heavy foot.

95 sc400 122k

 

got 120k on my sc300 running 17" at 35 psi tires all around and also just did a full tune up at change spark plugs iridium fusion bosch, bosch fuel filter, eneos full synthetic every oil change, seafoam. i get about city 22 and on highway 27. light foot no a/c half a tank close to 180 miles. i happy with it =)

 

After a recent wash and wax my car gets 5 more mpg and it has like 20 more hp.

 

SC300 w/ 138k miles. Only real mods possibly affecting mpg are lowered suspension, bigger wheels and wider tires. Averaging 22.5-23mpg with a mix of freeway (70-75mph w/ AC) and street driving.

 

Getting about 13-14 in the city with a singled 1jz. For some reason the AFRs I'm reading are in the mid 13s while the engine is in closed loop Anyone know something about this?

 

From my fuel calculator I average 13-14mpg in mixed local highway and city driving. This is mostly city. That's an accurate number from my corrected speedometer/odometer. The last long highway trip before some recent changes and speedo correction I netted about 17-18mpg. I've yet to do a really long highway trip in this thing.

I believe I could get slightly better economy if I had a more docile driving style and didn't routinely travel at 80mph in 5th so much. This is a 300 with a manual transmission, 4.27 Torsen rear end (not sure if having a Torsen affects fuel economy on the highway) and tires equivalent to the original factory diameter. No BFI, stock exhaust and totally stock engine with all maintenance up to date.

 

Im getting like 14mpg in the city and 22 on the highway, but I dont do much highway. I wonder why my city mpg is bad, my car oesnteven have clutter in the trunk.

 

One thing I wanted to add.............

I know that driving at 55mph is supposed to give the best fuel economy.

But driving like a tard at 55-60mph, not letting my rpm get any higher than 2300 got me 23 mpg.

When I drove 80-85mph with cruise control on, rpm 2600-3000, I got 24.7mpg.

So for my car driving at a slower speed does nothing for my gas mileage, not accelerating fast helps a lot though.

 

I'm pretty sure these cars were originally designed with 55MPH in mind for the best fuel economy in the USA. These days the federal 55MPH maximum limits have been done away with in most areas so it's less convenient.

Just a guess but the reason for the peculiarity may just be down to the engine not having to work as hard with 300-700rpm more to work with at highway speeds. It's a little more beneficial to keep a fairly constant rpm that doesn't have to be pushed on that much versus a really low rpm that is barely up to the task of maintaining the speed you want to be at.

In 5th gear in my car at 70mph I'm at 3,000RPM (speedo corrected). I may never hit the original maximum factory fuel economy numbers again in my car but I do find 3,000RPM cruising preferable to the 2,700-2,800RPM cruising I got with my old stock 4.083 gearing. The engine had no power and I almost always had to downshift to gain even incremental passing power, which threw me into a far more aggressive RPM in 4th. That would hurt gas mileage in and of itself on a long trip.

If I back off to 65MPH it helps quite a bit more and I think that may be the sweet spot for me. If I do happen to travel at 60MPH I might get close to the original factory fuel economy.

Avoiding downshifting helps a lot but keeping the engine from working too hard at its lowest possible cruising RPM is also good.

 

Just some of the other reference threads for people who are actually interested in the question rather than just in responding. There have been some solutions and hints in the past to improve your results.

 

Combined highway and city at last fill up for my SC400 was 23.87.

 

1997 SC400 17.9 city up to 25.5 highway with 19in ISF rims

 

I was hella happy when i got 200 miles on half a tank of highway driving in my 92 sc400, that was with 91 + octane booster lol