I feel like I am getting terrible gas mileage in my 1994 SC400. How much should I get to the gallon? Any way of getting better gas mileage? By the way, I never race, or accelerate past 3000 RPM, and I usually gave the AC on at LOW and only one bar on the A/C because its way too hot out here in So Cal. Help would be much appreciated.

 

Depends if its mixed highway-city....when i went to school, ie more highway, i would average around 21MPG on my 92. so i would get a bit over 400 to the tank.

 

I've heard that the 300 gets pretty bad gas mileage in the past (I actually heard that the 400 gets better, must be the gearing?) But on a recent highway trip I got 26.4mpg mostly highway, switched the A/C on and off depending on how much I was sweating to death and how foggy the windows were.

My car has gotten somewhat better mileage since I:
Changed to synthetic oil, got a new cap/rotor (does the 400 use a distributor?), changed the tranny fluid, changed the rear-end fluid, and switched to 91 octane instead of 93. So if you haven't already, do a tune-up, and try different gas.

Also, I've heard (I have found no proof of this) that on most normal cars (ones with a good amount of their torque down low) if you drive in your highest gear right at your peak torque, you'll get the best mileage; as this is where the engine is operating most efficiently. For instance, most of my trip was done at around 80mph (3.1k or 3.2k on the tach, I believe that the 300 has it's torque somewhere up higher than most; again not exactly sure on that) And I was very impressed with my mileage. On my way to work, which is about 70mph on average, I will usually get 22 or 23mpg with little to no A/C.

I don't know much about California, but I assume you do mostly stop-and-go type traffic, and I'm willing to bet that is what's killing you. Also, try sweating it out one day if you're just heading home/ somewhere that no one's going to care if you're all sweaty. I've found I can survive a whole lot of heat on that drive home.

Also, for a long time, I was only using 93 Octane from Shell (V-power), but recently switched to 91 from another station in the neighborhood. I've noticed a slight gain in MPG from that. From what I have heard it is easier to burn lower octane fuel, and since my 300 says it was designed for use with 91, I'll stick with it.

You may find this information useful as well Acetone added to gas

I have not yet tried Acetone, but I think I'm going to here in a week or so. Experiment and see what you can come up with.

Sorry about the long post, didn't realize I'd written so much. Good luck!

 

you have a 400 that shifts at 3000rpm? when i'm in normal driving, i find it shifts at 2000rpm... and i get around 19-20mpg in the city and if i went all freeway, around 25mpg.

 

I used to have a 92 SC300 that shifts at 3000rpm (regularly). I don't know why it did that.

 

Saving GAS by ETC off ?

--------------------------------------------------------------------------------

Miles / Gallon Average M/G
248.9 / 15.39 16.17
305.5 / 18.88 16.18
214.1 / 11.389 18.799
309 / 18.8 16.44
184.2 / 11.284 16.32
219.2 / 13.677 16.027
258 / 16.9 15.266
309 / 18.748 16.482
227.1 / 15.55 14.61
312.3 / 18.6 16.79
195.9 / 10.415 18.81
271.9 / 17.52 15.519
232.1 / 15.402 15.07
243.3 / 15.683 15.514

These are my recent gas consumption rate on my SC4. Almost of my driving is local city drive and I drive pretty fast. From home to work is 10 miles each way (all local with bunch of traffic lights) I was kind a curious also about this ETC, so I set it off few times and drove all the way to empty the tank.

14 or 15 are when ETC was on and off. (mostly on)
16 is when ETC was off.
18 is for long freeway driving.(couple of hours)

I just don't like the slow responces on tranny when ETC was off.
Since I did not see much difference on saving gas, I do not care anymore. I usally leave it on.

It became my habit to keep the GAS log. I reset the trip odometer every time when I fill it up. I write down the miles and gallons next time when I fill it up. This way I know exactly how much gas my SC uses, and I can detect immidiately if Gas consumption rate goes up caused by some part failure also.
Editting "Note" feature on my BlackBerry is handy

 

14mpg FTW!!! Drivetrain loss (which we have no lack of) and overcoming momentum (ie, the 3600lbs of lard we call the SC) causes for very poor in town fuel economy.

 

I get about 19mpg average with mixed city /highway in a 95sc400

I also have BFI, no mufflers, full synthetics throughout. I noticed about a 1mpg increase after the exhaust and changing to synthetic




Your right it sucks and the cars should get better mpg. I had a 350hp 96' Z28 that averaged 25-30mpg but it was a 6speed.

 

During stop-and-go city driving, it's estimated that overcoming inertia is responsible for about 35% of the vehicle's resistance. Driveline friction is about 45%; air drag is about 5% and tire rolling resistance is about 15%.

Overcoming inertia no longer plays an appreciable role in the vehicle's resistance during steady speed highway driving. For those conditions it is estimated that driveline friction is about 15%; air drag is about 60% and tire rolling resistance represent about 25%.

The previous statements are found at tirerack.com. You'll soon find that the cars weight, drivetrain loss, and rolling resistance has much more to do with gas mileage then "performance output" of the engine. Thus you could put a civic motor in our chassis and it would get the same gas mileage as the 2JZ.

 

just filled up my 92 sc300 5speed with 160xxx mi. got 380 miles on 16.5 gallons. so like 23mpg which is better than my 96 automatic. mixed city/highway driving

 

i get bout 400 miles on my 93 sc .....

 

I don't even want to talk about it. The money isn't killing me but it is painful to have to fill up so often.

 

Does the A/C really affect fuel consumption that much? I don't notice much difference (I let the auto settings do it's thing) when the A/C is on or off. Most of the difference is in the type of driving you're doing (freeway, suburban or city stop-starting). In my Soarer I'm averaging about 12~13L/100kms, so usually that's getting me about 500~550kms from a tank. My car's stock too so when I get some time to free up the exhaust and intake it should improve a little.

 

Currently experimenting with mine. So so far, I have trip A set for gas mil. and trip B set for the next time I need to do a oil change. After I figure out my numbers, I'll post it. It sucks not having VVTi and not getting as much miles per gal. as my Dads 06 BMW.

 

A/C will have a little effect with in town driving, highway driving makes no difference. In town it can make 1-2 mpg difference which isnt enough for me to worry about (if I was that worried, Id sell the sc and go buy a civic/accord/something that didnt get 14mpg).