I have an 01 is300 and ever since I got the car the mpg has been bad. I changed oil air and spark plugs (nkg plat didnt know I needed iridium oem denso) and no changes. The car does not run bad at all from a performance aspect.

 

The car has only thrown 1 code about something in the evap fuel tank system. The code went away on its and did not effect the cars drving either way. I had a modded Grandprix GTP before so Im entirely stumped with this.

 

How are you calculating your mpg?
Can you smell unburnt gas or anything like that?

 

On a full tank I drive about 200 miles and Im empty using digital odometer. I have smelled fuel before but cant remember the last time it happened or where.

 

Calculate it this way....

-Fill up a full tank
-Reset odo
-Drive till the gas light comes then fill up another tank
-Record mileage driven since last fill up
-Divide the mileage by how many gallons it took to fill up the tank.

But if you are only getting ~200 miles for a full tank regardless of how you are calculating, then something is definitely wrong.

 

What's the average miles that you should be getting to a tank?

 

About 350+ should be the mileage from full to empty according to a friend of mine that has two supras and 2 gs

 

driving habits are #1 cause... can you give us an idea of how you drive?

other than that, sounds like you have done the basics and if it seems to have good power, its hard to say...

 

Looked over it with my friend today. We found a a couple of vacuum hoses disconnected and uncapped. Also my pcv valve, valve cover gasket and seals are shot middle plugs were drenched in oil. Today we could only fix hose problem and the car feels even smoother. I gotta give these cars credit with all these things wrong it didnt throw a code or drive horrible *aside from mpg*. Once I change whats wrong Ill let you guys know if the mpg problem persists.

 

I've only had my 2001 IS 300 for about 8 months. Typical MPG is 22-24 (suburban driving, usually short trips). I've found that if I get "aggressive" I can pull that down pretty quickly. Now that it's summer, I seriously think running the A/C has impacts my numbers also. I got 18 MPG a couple tanks ago. Now I toggle my A/C (cuz' I hate to buy gas).

But 11 MPG sounds really low. Of course, this raises an interesting question. If I took my car out to the track, what's the lowest number I could achieve? That would be an interesting reference point.

 

Assuming a bone stock IS300 that makes 215 hp at the crank, at 5800 RPM, you would be utilizing approximately 1300 cc per minute of fuel (normal fuel, add 40% or so if E85)... 1300 cc works out to .34 gallons per minute... through the auto transmission, this fuel consumption would occur at full throttle at 5800 rpm, approximately 126 mph in 4th gear, or 144 mph in 5th gear... Assuming you could get to and maintain 144 mph, you would be consuming 20.4 gallons per hour, and at 144 mph, you would be getting 7.05 mpg. in 4th gear at approx 108, 5.3 mpg, at 76 mph in 3rd, 3.7 mpg... In the lower gears, however, you don't need to use 100% power to maintain those speeds, so, it will actually be less mpg than I just said, those are just worst case under hard acceleration at peak HP...

They are also theoretical numbers, obviously, based on horsepower production, approximately how much fuel it takes to make that power, etc...

Top Gear did a test of super cars, all 400+ hp cars, and on a road course track they averaged between 3 and 7 mpg...

 

i run my ac non stop. tend to start my car and have 10 min conversations and get about 250 mi or so on a tank if that helps any

 

Guys I replaced everything I had to and the car feels like it took a time machine back to 01. Ill let you know what I avg on a full tank now.

 

im getting 270 miles per tank fill up, is that normal?

 

IMHO yes.

I get 19 mpg around town, ie about 240 250 per tank.

On highway at good speed 23 -25 mpg. max about 350 - 380 per tank.