15mpg.. WTF

[ragman]

Winter Gas for sure is not helping with the MPGs.

[ehsnils]

Winter Gas for sure is not helping with the MPGs.

 

Winter gas is at most a 2% change in the consumption.

 

The rest attributes to increased oil viscosity and longer period of warm-up program where the engine and gearbox (for AT vehicles) management changes the settings to speed up the warm-up of the engine at the cost of increased fuel consumption.

[ehsnils]

I'm still having the same issue except I'm getting ~13mpg. I've tried plugs, coils, both cats replaced, cleaned injectors, fuel lines and throttle. I'm going to have my ecu tuned but they can't fit me in `til January.

 

You can probably do a data log already and have it assessed by others here.

[specialB]

I daily drive with 850cc injectors. I drive mostly highway and I get 250-300 out of a tank on average. Soo with mostly highway miles im averaging 16-20mpg with a 5mt. Back when the car was stock and I used the economy map with the accessport and managed 450 miles to a tank just straight highway, thats 30mpg!!

[laff79]

welcome to having a modified Subaru turbo 5eat

[BarManBean]

welcome to having a modified Subaru turbo 5eat

 

Yup. It's unfortunate, but the 5EATs just crush some gas-o-maline.

[laff79]

I stopped monitoring the mpg over a year ago. That little screen will remain a temperature gauge from now on.

[rob-2]

Yup. It's unfortunate, but the 5EATs just crush some gas-o-maline.

 

I agree.

 

Right now with the temps in the 20's I'm getting around 17mpg mixed driving.

[specialB]

denser air = more fuel to compensate = shittier mpg + roof rack = might as well be driving a tahoe.

[chisav]

My 5MT stage 2 infamous tune driving ultra conservative I'm able to get around 320 miles per tank highway and city. Regular with some spirited driving and mostly city 280ish. Sucks being modified when it comes to gas.

[iNVAR]

denser air = more fuel to compensate = shittier mpg + roof rack = might as well be driving a tahoe.

Denser air = more power, IF your foot is calling for it.

 

Denser air just means you have to suck in a smaller volume of air to get the same mass of oxygen necessary to mix with your fuel. This means you can cram in more oxygen into the cylinder, but again, ONLY if you demand it.

 

If you drive the same way in winter as you do in the summer, then the density of the air is not what's responsible for crappy mileage.

[ssbtech]

And the auto industry is telling us that small displacement turbo engines is going to help with fuel economy.

[iNVAR]

Heheh, not if you drive it like it has 8 cylinders.

[golunnova]

2008 LGT 5EAT, Stage 2 protuned. I get around 17-18 city and 23-24 highway. The stop and go traffic in the 5 boroughs just sips my gas away...

[covertrussian]

I track my MPG religiously in a spreadsheet on all my cars along with driving style, mods, etc. for that fill up. I purchased my LGT in beginning of November, which probably means I've only filled it up with winter gas.

 

My 5MT LGT gets ~16/25, using the old fashioned miles driven divided by gallons filled up. Don't trust the gauge, I've had the gauge off by up to 15%.

 

100% city driving I get around 16mpg. This means stop lights, 25-40mph driving mainly.

Highway is 24-27mpg. I think installing a catless uppipe actually hurt the highway MPG's because the turbo spools too fast now.

 

And the auto industry is telling us that small displacement turbo engines is going to help with fuel economy.

 

There are a ton of factors that cause stock turbo cars suck on gas.

 

• Compression is a big one, just about all non direct injected motors run around 8:1 compression ratios.
  
• Tiny turbos that have no lag
  
• Stock turbo motors are too rich, 10-11 AFR's is stupid rich.
  
• Overly safe timing maps, OEM cars have to be able to take 87 gas just in case...
  
• Restrictive exhausts, ton of cats, not efficient tubing (look at our downpipes).
  
• Tiny Spark plug gaps, safety measure to prevent spark blowout
  

 

 

I have a turbocharged Infiniti G20, I'm getting 20mpg city and 36mpg highway on it. I think city is so low because I haven't fully tuned the city portions of the map.

 

Mods:

Stock 130k mile SR20DE motor (2.0L) with 9.5:1 compression, GT28r, 3" exhaust, 11.8 AFR, Iridium plugs with .045 sidegap. The car put down 235whp on a mustang dyno with 10.5psi.

[ehsnils]

Still - winter gas is at most 2% of the fuel consumption - that by itself is hard to measure.

 

What really happens is that the engine warm-up phase is longer where the engine is burning more fuel before it's warm just to speed up that process. It's very noticeable on AT gearboxes that shifts up a lot later until the engine is warm.

 

The oil in the transmission is also a lot thicker when it's cold.

[covertrussian]

Still - winter gas is at most 2% of the fuel consumption - that by itself is hard to measure.

 

What really happens is that the engine warm-up phase is longer where the engine is burning more fuel before it's warm just to speed up that process. It's very noticeable on AT gearboxes that shifts up a lot later until the engine is warm.

 

The oil in the transmission is also a lot thicker when it's cold.

 

Winter consumption used to eat a higher percentage of fuel economy during the MTBE times. That's because summer gas was 100% gas and winter blend had MTBE as oxygenate additive. Since MTBE was determined harmful and ethanol switch began nationwide, they started adding ethanol to summer gas too though. Thus the difference between summer and winter consumption became smaller due to having worse gas mileage even in the summer. Ethanol is less efficient because it burns at a lower BTU, sure it does have a higher octane rating but as we all know higher octane does not equal to more power/better fuel economy on a regular 87 motor.

 

This is why LGT's EPA gas mileage went from 19/25 to 17/23, after ethanol was mandated. Around the same time EPA changed the process of measuring the MPG's too. This also resulted in lower fuel economy, thus EPA just said, for all cars tested before 2008, we are going to remove a certain percent from their current numbers. My car still gets the old EPA's rating highway, it actually got better, 27.8mpg, before catless up pipe/new O2.

 

Start up times are probably the biggest killer for winter fuel economy. Lower temperatures means thicker oil which means more friction indeed. But another gremlin is cold start AFR's, fuel trims, and O2 sensor efficiency. Since fuel doesn't atomize as well when your intake manifold is cold and since you have more oxygen in the air, your air to fuel ratios are crazy lean, thus you have to add more fuel. Another one is the O2 sensor, it's generally ignored until the heater element properly warms up. On most cars O2 sensor only is used after 125*F. Once it's used for closed loop feedback, your AFR's should bounce up to 14.7 and your good to go.

 

On my turbo G20, I used to run straight of the map, no O2 sensor. Because of that even after 125*F my AFR's still would be fairly rich. When I wired in my O2 sensor and used it for feedback, my city MPG jumped up 2-3 MPG. Less fuel was being wasted with constant city cold starting.

 

Back to oils, manual transmission fluid is actually much thicker then ATF, so technically manuals have it worse, but since we do the shifting ourselves, only slight friction increase is what hurts the MPG. Automatics are definitely more needy, and less efficient overall.

 

There is definitely a ton of factors that hurt winter gas mileage, with a proper setup and tune you can regain a few MPG's. I haven't started tinkering with the ECU on my Legacy, I'm first doing bolt on mods to improve power/mpg. Once I get that all setup I'll switch over to fine tuning the ECU and we'll see what the Legacy can do.

[z28dreams]

Same. I have an '05 5EAT and get around 15-16mpg in city driving (though I take very short trips which is awful for it I'm sure). Highway is probably averaging around 25mpg overall.

 

I talked to another guy that had one and he said that he also had really poor mileage on his 5EAT.

 

I've checked tire pressure and replaced the air filter, but no change. (Tested on both stock rom and open source stage I). I haven't swapped spark plugs yet, but I don't suspect it would make a big difference since the car is only at 42k miles or so.

[covertrussian]

Same. I have an '05 5EAT and get around 15-16mpg in city driving (though I take very short trips which is awful for it I'm sure). Highway is probably averaging around 25mpg overall.

 

I talked to another guy that had one and he said that he also had really poor mileage on his 5EAT.

 

Man so I'm getting as bad gas mileage on my 5MT as you 5AT guys, I guess I do live in the mountains and it is all 5 miles trips before car is shut off.

 

I've checked tire pressure and replaced the air filter, but no change. (Tested on both stock rom and open source stage I). I haven't swapped spark plugs yet, but I don't suspect it would make a big difference since the car is only at 42k miles or so.

 

You would be surprised how much spark plugs matter actually. I would pull one out and look at it's condition and replace it if needed.

[freaksavior]

I get about 19 on average which is way better than the 7-11 I was getting in my dads '95 Dodge Ram 1500 with the small v8

[gimpydingo]

When I bought my 07 LGT 2 years ago I was getting around 19.8 MPG, though I drove it more in I and S modes. Over the past year I was getting around 17.4 - 18 MPG then it dropped. I had a dead O2 sensor. About 2 months ago I finished a STG1 tune and now avg 16.5 MPG.

 

My driving is mixed mountain (5 - 7 miles up hill), hwy, stop and go. Once on the hwy I get in the commute lane and get maybe 10 miles @ 65+ MPH.

 

I could probably get closer 18 MPG. The wife likes to push the pedal to the metal and/or leave it in lower gears while shifting, drinking down that tasty gas.

[solo413]

Damn I thought it was just me... I average 16 to 19mpg and have to fill up literally every 3-4 days & as you all know 93 is not that cheap!

 

I drive stop n go and lots of back roads to work everyday roughly an hour commute one way n 20 mins of it at about 40-60mph with no stops.

 

I changed spark plugs twice in the past year, tried gas enhances n even have ap3 tuned to Eco for a while nothing changes the mpg! At this point I have decided to eventually get a gas saving car in the next year n keep LGT for fun n scca races.