High Fuel Consumption Issue - ?

[4DR_DB7]

I've noticed I don't get as great MPGs out of my 1.8 non-vtec b18b as I expected. Key points:

1) According to my owners manual, my fuel tank capacity is 12-13 gallons, yet every time i've filled up, i'm only getting 10-11 gallons... and i've been waiting until the "low fuel" light comes on .

2) When the fuel gauge is more full (above half) I seem to get much better mpgs, however, once the gauge dips below half the fuel seems to burn up real quickly.

3) I'm getting about 275-300 miles per tank, which according to the stated capcity of 13 gallons, is only about between 20-23 mpgs... and this is with 90% driving on highway. I also rarely cruise over 4000rpms.


I guess I expected closer to 25-30 mpgs out of the 1.8L, since my last car had a 2.5 4cyl and got closer to 30 mpgs. Could it be because i had a less restrictive intake and exhaust system than my current car?

It almost seems like there is a balloon or something in the fuel tank which is causing it to not fill up all the way, and thus throwing off my calculation and causing my fuel gauge to read 1/2 full, when there is really much less fuel than that.

Anyone had any ideas, or am I just expecting better mpgs than I'm going to get? If so, man, an LS-Vtec must be a gas-guzzler.

[probevette]

when the light comes on you still have a reserve of a few gallons left. so that should be the missing 3 gallons

[marshallpre1]

300miles/11 gallons= 27.3mpg

looks good to me

My Supra last fill up...
163miles/11.8gals= 13.8mpg (I'm way way way too rich, need to lean it out I know!)

[DPancoast]

You can't go by what your manual says. The proper way (most accurate without actually running your car put of gas completely) is to fill up and don't top off, reset your trip meter, drive till the light comes on, fill up again (again.. no top off) and divide the total miles on your trip meter by the gallons you put in.

You'll never use all of your gas between fillups so it's useless to use your empty capacity.

It's also very common in a lot of cars for your fuel gauge to drop faster below the halfway mark. I forget why, but a lot of cars do that. There are SO many factors that can affect your MPG as mentioned above besides the obvious throttle input.

- Tire pressures/rolling resistance
- ignition component wear (besides plugs also remember wires, and distributor cap and rotor)

Etc. Honestly you're not that bad off as it is but I see what you're saying

[Z31Fanatic]

You're not doing your calculations right.

Fill up your tank (full). Reset the tripmeter to 0 then drive until you need to fill up again.
Fill up your tank again and look how many gallons it took. Now look at the miles you've driven between fill ups.
Lets say you drove 300 miles and you put in 11 gallons of fuel. Divide 300 by 11 and you get the gas mileage. That's the only way you can calculate fuel consumption.

Also you should know that when the low fuel light comes on there usually is 2-3 gallons of fuel left in your tank.


Edit: sorry, I didn't see Dpancoast's post. Basically the same thing.

[4DR_DB7]

1. As directed; I did (2x) fill up my tank to full, reset tripmeter, drove till light came on, divided miles driven by fuel tank capacity --instead of the amount that I filled up with.

Problem with the way u guys are describing, is I don't use the full 11 gallons that I filled up with, or I just more than the 11 gallons I filled up with, its going to throw off the math. Like, say I fill up with 11 gallons, I drive 300 miles till the next fill-up, but unbeknownst to me, I only actually used 10 gallons... But I would calculate 300 divided by 11, or vice versa if I used 12 gallons. argggh!

I am probably due for new plugs.. that might help a little bit i guess. Motor feels very strong though, doesn't appear to be any issues. I'm wondering if a good sea-foaming would help too. I already use a fuel injector/system cleaner.

2. Since its a floating tank, the light will come on, then go off, then come on again. Its tough to get an accurate idea of when the tank is actually nearing empty. So i've just been using the first time the light comes on as my barometer. I guess there could be 1.5-2 gallons left in the tank, eventhough the needle is on "E".

[Metal4all6]

I think you're looking at it the wrong way. As others said, start off with a full tank of gas and reset your trip odometor to 0. Next time you fill up, you take the miles driven divided by the number of gallons it took to fill your car to the top (not total tank capacity). That'll give you the MPG.

You don't need to wait until the low gas light comes on to find out MPG. You can do it with a half tank, 3/4 tank, or whenever, as long as you reset the trip odometer last time you filled up to full.

Also, I've always heard that the reason why the 2nd half of the tank goes quicker is because of the shape of the gas tank. I think alot of them are shaped sort of like a 'V'.

[97TurboDSM]

what? if you're filling up when the light comes on and you filled up 11 gallons, what in the world makes you think you should divide the miles by a number higher than what you filled up with? that makes literally, no sense.

[Z31Fanatic]

That power outage last week must have screwed up his brain too

[4DR_DB7]

Because you don't fill up with the exact same amount of gas left in your tank everytime.....

eg. My gas light could come on and I could fill up with 2 gallons still left in the tank...

next time the light might come on and by the time I get to the gas station there is 1 gallon left in the tank..

that would throw off the calculation.

Point is, with my driving being 90% highway, the motor being 1.8L non-vtec, I expect better mileage and think something else may be robbing it.

[Z31Fanatic]

I don't understand why are you still confused. It's a simple calculation which we told you how to do it.

[twastheglow]

This thread makes me laugh out loud.

[4DR_DB7]

You guys are clearly misunderstanding the situation, and I'm obviously not doing a good enough job of explaining. My bad.

Cliff Notes: My car should be getting better than 21mpg highway... and should not get 30-35 mpg on the top half of the tank, and 15-20 mpg on the bottom half. WTF.

CLOSE THIS MODS! (I'll keep all the Doubting Thomas's updated with a big "I told you so" thread when I find out what the culprit is)

[twastheglow]

Originally Posted by 4DR_DB7

You guys are clearly misunderstanding the situation, and I'm obviously not doing a good enough job of explaining. My bad.

Cliff Notes: My car should be getting better than 21mpg highway... and should not get 30-35 mpg on the top half of the tank, and 15-20 mpg on the bottom half. WTF.

CLOSE THIS MODS! (I'll keep all the Doubting Thomas's updated with a big "I told you so" thread when I find out what the culprit is)

LMFAO! For one, don't calculate the "top" and the "bottom" as two separate entities. It has to be calculated as a whole for reasons that have already been stated. Listen...drive your car to my house and give me $100 and I'll tell you what you're MPG is.

Joking aside, I understand your concern, but it has been explained a good 4-5 times now what you need to do. Just do EXACTLY that then report back.

[russiankid]

When I calculate my mpg I do as described above. However, if my mileage is 377.7 miles, I take that exact number and divide it by the exact amount of gallons that went in.

Sounds like you're just trying to find out how many mpg's you can get with less fuel as your car weights a bit less with it so its less drag.

[DPancoast]

if your gas light goes on... then off... then on... then off..

just keep driving lol. When it stays on... then you're low.

ALSO... don't take my word for it... just saying from my experience with my MR2.... when my light flickers... I still have plenty of time.

[4DR_DB7]

I've properly calculated my mpgs. :D and they are lower than they should be. thanks for the input. I'll let you all know what I find out.

[TrboChicsRock]

Originally Posted by 4DR_DB7

1. As directed; I did (2x) fill up my tank to full, reset tripmeter, drove till light came on, divided miles driven by fuel tank capacity --instead of the amount that I filled up with.

Problem with the way u guys are describing, is I don't use the full 11 gallons that I filled up with, or I just more than the 11 gallons I filled up with, its going to throw off the math. Like, say I fill up with 11 gallons, I drive 300 miles till the next fill-up, but unbeknownst to me, I only actually used 10 gallons... But I would calculate 300 divided by 11, or vice versa if I used 12 gallons. argggh!

You're calculating it wrong because you're using the amount of gallons you put in your car in the first fill up. What you do is fill up your car and reset the tripometer. Then the next time you get gas, you have to fill your tank again and you take the amount of miles you went and divide that by the number of gallons you put in on your second fill up.

[twastheglow]

Originally Posted by DPancoast

You can't go by what your manual says. The proper way (most accurate without actually running your car put of gas completely) is to fill up and don't top off, reset your trip meter, drive till the light comes on, fill up again (again.. no top off) and divide the total miles on your trip meter by the gallons you put in.

You'll never use all of your gas between fillups so it's useless to use your empty capacity.

It's also very common in a lot of cars for your fuel gauge to drop faster below the halfway mark. I forget why, but a lot of cars do that. There are SO many factors that can affect your MPG as mentioned above besides the obvious throttle input.

- Tire pressures/rolling resistance
- ignition component wear (besides plugs also remember wires, and distributor cap and rotor)

Etc. Honestly you're not that bad off as it is but I see what you're saying

Originally Posted by Z31Fanatic

You're not doing your calculations right.

Fill up your tank (full). Reset the tripmeter to 0 then drive until you need to fill up again.
Fill up your tank again and look how many gallons it took. Now look at the miles you've driven between fill ups.
Lets say you drove 300 miles and you put in 11 gallons of fuel. Divide 300 by 11 and you get the gas mileage. That's the only way you can calculate fuel consumption.

Also you should know that when the low fuel light comes on there usually is 2-3 gallons of fuel left in your tank.


Edit: sorry, I didn't see Dpancoast's post. Basically the same thing.

Originally Posted by Metal4all6

I think you're looking at it the wrong way. As others said, start off with a full tank of gas and reset your trip odometor to 0. Next time you fill up, you take the miles driven divided by the number of gallons it took to fill your car to the top (not total tank capacity). That'll give you the MPG.

You don't need to wait until the low gas light comes on to find out MPG. You can do it with a half tank, 3/4 tank, or whenever, as long as you reset the trip odometer last time you filled up to full.

Also, I've always heard that the reason why the 2nd half of the tank goes quicker is because of the shape of the gas tank. I think alot of them are shaped sort of like a 'V'.

Originally Posted by TrboChicsRock

You're calculating it wrong because you're using the amount of gallons you put in your car in the first fill up. What you do is fill up your car and reset the tripometer. Then the next time you get gas, you have to fill your tank again and you take the amount of miles you went and divide that by the number of gallons you put in on your second fill up.

ahahahahahahaahahahahahaahahahah!

What you need to do is fill up your tank and reset your tripometer. Then, once your gas light comes on, fill it back up again and look at how many gallons you put in the tank. Then divide that by the number of miles you have on your trip.

If still confusing, please let us know and someone else will explain it.

LMMFAO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

[4DR_DB7]

rofl....