Fuel weight
 

Just a thought that I haven't previously seen posted. Every one knows that gasoline weighs around 6 pounds per gallon. Have any of you put smaller tanks on you cars or do you only put 2 to 5 gallons in at a time?

I seem to remember that every extra hundred pounds in a vehicle costs about 1% in fuel economy. So If a max of 5 gallons were used instead of a fillup of say 12 gallons, that would save around 42 pounds of weight on a consistent basis. If a smaller tank were installed you might save anothe 5-10 pounds in weight.

Just wondering if anyone has done this yet.

JJ

Probably, but with People who drive Jeeps as a recreation, All I hear from them is adding ANOTHER tank to their Jeep so they can go farther without filling back up again.

It'd be even more with an SUV, especially because some tanks are up near 40 or 50 gallon tanks. or even more. Mine's a 23 gallon tank.

It's probably been done, although I don't know of anyone here that does it. The only problem I see is less accurate fuel data if you don't have instrumentation because you have less gallons to judge on every tank, you you mileage might be crazy high one tank and really poor the next if you only had 2-5 gallons to take measures from.

I have run multiple 5 gallons fills in a 15 gallon tank with no appreciable increase if FE. It does accelerate better but it was a hassle to fill up every 2-3 days. There is no doubt that lighter equals better FE but I don't think that this is something that will show up on the fuel gauge. Kind of like getting rid of the spare. In the long run I want to get home. YMMV.:turtle:

Try 5 gallons in a 50 gallon tank. that'd be like getting rid of all your friends who need rides! :D

Actually 5 gallon in a 50 gallon tank is probably less percentage wise then the other way around just because of the empty weight of the cars if taken as a percentage. Don't know but if it has a 50 gallon tank all 5 gallons is going to do is take you to the gas station to fill up again.:D

yea, but who takes that into factor? wait.. I do CRAP! I wonder what a geo would look like with a 50 gallon tank *ponders*

I'm torn between wanting to calculate my actual fuel consumption (by doing a complete fill up) and wanting to minimize weight (by doing more frequent small fills & then relying only on the SG to tell me my FE).

If I could easily remove fuel from the tank after filling up, I'd keep it in gas containers and add it back as needed until the next refill.

I've tried syphoning from this car's tank before, however (when I bought it - to remove the 7 year old gas that was in it), and I couldn't get a hose into the tank. Ended up having to get under the car & remove the filler pipe from the tank to get the tube in.

It's too bad there wasn't an inflatable bladder inside the gas tank. You could inflate it to 10 gallons in a 15 gallons tank and fill'r up with just 5 gallons. :thumbup:

There's some lateral thinking!

Perhaps this thread applies more to those who already have extremely high efficiencies. If one is already getting 50-60 mpg I would think it unusual to run out of gas with a 200-300 mile range(4-6 gallons).

Great idea. Just have to keep it away from the fuel output line.

Which leads to a question I've been meaning to ask. Does the SG actually calculate the fuel economy or is it reading that info from the vehicle's onboard computer? I understand that the SG can tell you how much fuel is left in the tank by doing the full tank calibration sequence, but since it already reads the fuel efficiency before the tank cal is performed, then one of the two previous assumptions must be true.

Lazarus, if the vehicle accelerates better I would have to think that is due to the lighter weight. However, because of the lighter weight and the fact that an increase in acceleration is noticeable, maybe backing off on the throttle upon acceleration would make the difference in fuel economy more apparent.

Again, these are just a few thoughts I have. Other than the fact that for years I haven't filled my gas tank completely unless going on a longer trip, I haven't actually tried any readings myself as my new SG just showed up yesterday. And it works in both my Fords. Only the unit itself was sent(no cable). Just glad it wasn't a bad cable.
JJ

ten pounds =one horsepower power
 

ten pounds =one horsepower power at least that was what was said at the drags. is it worth it? some highline cars use aluminum jacks

I should also note that the 2G CRX HF has a gas tank that is about two gallons smaller than other 1988-1991 CRXs. This would reduce weight both my holding less gas AND from the smaller and lighter tank. And Honda apparently thought it made a big enough difference to actually put into production. Of coursethe HF also gets significantly better mileage than other CRXs, so a smaller tank is needed for the same range.

I will verify this information for those of you who don't know CRXes, I've always wanted to do the swap with someone else...mehbe one day!

If that's true then I think it would definitely show up. Is there a source for that you can link us to.

It's certainly not that pronounced. If so my 60hp engine would have a hard time moving my 2500 (laden) crx around, :turtle:

i think he means 10 extra pounds equals using 1 more horsepower. or so this is what I'm getting. 10 more pounds cruising where it would take 20 horsepower would now take 21.

For a fuel station first you have to slow down, then maneuver all around and stop.
Then start back up, maneuver out of there and accelerate back into traffic.
You would have been way better off if you could've kept on going.

So first it hurts FE just to pull into a fueling station, then the weight of the fuel in the tank has gravity pushing down on it hence offsetting the entire benefit.

Always fill'er up, the more times you have to stop for fuel, the worse your mpg.

The one thing I found helps is budget fuel, as in set aside a limited amount of monthly money you can spend on gasoline and obey your budget!, Budget is King, budget is Queen, whatever suits you but budget rules. Now either you have enough fuel or you don't... You can do the budget weekly if that works better, doesn't really matter but track it and obey it and always fill her up.

Compensating for the fill up by lengthening the time interval is fine.
So for instance if you set aside 20 a week and it takes 30 to fill the tank, I would guess you'll be filling up about every 10-11 days, but 30 a week is 1560 a year or 130 a month <- It is these figures that need to be tracked, doesn't matter what it costs to fill up so long you never go over the total, and if you do then you're doing it wrong but first time that is ok just start over then do it right lol.

I do not know if 20 a week is enough, you have to figure this out, make it a bit tight but not too tight, but if you find room for improvement feel free to use it. Mine's $10 a week, I only drove maybe 4,000 miles last year, this took some doing and so don't be discouraged if it takes time, but after some years I feel at home with my fuel budget.

...............
btw a gallon of water weighs 8 pounds, fuel is slightly lighter but not much.
budgeting fuel money can also help one spot FE-related driving mistakes but also wasted trips, certainly the number of friends who used to ask me for a ride went down in amazing record amounts at the mere mention of the word budget lol
That's why I say, budget rules.

I understand you're elaborating on the previous comment (I'm just clearing up that point).

Given the same vehicle with say 2500lb and 2490lb. If the 2500lb variant requires 20hp to cruise - the 2490 will also require 20hp to cruise (okay, maybe 24.9982 due to incredibly smaller rolling resistance by comparison).

The above assumes on a flat and stead state cruising.

The big benefits (FE wise) of reducing weight come into play during acceleration :thumbup: This is why weight is such a big deal for city driving cars and why you're more likely to hear such information at a drag strip :)

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For fuel ups.... I personally go for a full top off. I'd rather not allow more opportunities for smog fumes (I wouldn't be as concerned if my state required EVAP recovery on all gas pumps). I also don't want the extra time it takes to do so. I also live in a pretty flat area - so things balance out :p

Not if you're pulling up to the pump at the end of a glide, and you depart on a pulse.