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Sadly Gregg has passed away
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Discussion Starter #1
Time to debate....some might see this issue as trivial, but I find it interesting. Would appreciate member opinions! My morning coffee clatch buddies almost came to blows on this one!:biglaugh:

Question: Is it more advantageous to gas up when your tank reaches 3/4 full or wait until less than 1/4 full?

Coffee clatch member opinions.....

1) Filling up at 3/4 means any contaminated or off spec fuel is 75% diluted. (Tank Truck Driver)

2) Filling up at 1/4 or less keeps gas from "getting old"! (Waitress)

3) Filling up at 3/4 minimizes tank vapor space and loss of light ends, thereby preserving octane # and specific gravity. (Refinery Lab Guy)

4) Filling up a 1/4 or less causes an in tank fuel pump to run hotter (less gas to serve as a heat sink) causing premature pump failure. (GM Mechanic)

5) Uhhh...OK...too much coffee....let's all calm down? (SLKWorld Member)
 

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Don - Founding Member #4
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:)Around 1/4 tank left, when it's convenient. Fill it up to the brim. Less stops during a life time.
 

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On this side of the pond, with uber high fuel prices, some people advise not to drive round with a full tank, as you're carrying weight around for no reason, and it wastes fuel.

Personally, I never let my tank drop below 1/4. Just incase there's any gunge in the bottom of the tank.
 

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Premium Member 2006 SLK 280-sold
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3,552 Posts
Less than 1/4 a tank

Well if your gas gauge doesn't work. . .

It forces you to reset the trip odometer every time you fill up, and then when you get to 400 miles you stop and fill up again. At least you get a measure on your gas mileage every fillup.

I guess I never thought about bad gas when I'm buying premium from a "Top Tier" station.

BTW it goes 450 miles before it runs out.

When it coasts to a stop it's on 450.2

:)
 

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Premium Member
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When the light comes on (around 1/8 tank), to the brim with Shell V-Power.
 

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Sadly Gregg has passed away
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Discussion Starter #10
Dead on Woolly! The tact of our original conversation was more about what's best for the car rather than most convenient for the motorist. Seemed amusing to me....thanks for your thoughts!
 

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Premium Member 1998 SLK230
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3,514 Posts
Fill up at 1/4 tank or less, and dont top off the tank.

The fuel is taken from the bottom of the tank right!
so any impurities that settle there are used, so you need to keep the fuel sloshing around so those impurities dont get used:biglaugh:
 

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When you need fuel, put some in.

It'll never go stale if you drive normal mileage, filters will take care of any crap.

I was most surprised when a couple of years ago I couldn't start my lawn tractor. It hadn't been used from October to April. The mower mechanic that came to service it said "It'll be the petrol gone off". He drained the tank, filled it and it started first time. Really surprising, I knew that fuel went stale, but not that it just wouldn't fire.
 

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Premium Member 2006 SLK350
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6,796 Posts
Around town as needed (agree with tatts - tankering fuel costs you, we never do in the aircraft now); allows you to get the best price. If you're going on a jaunt - fill er up! Never know when you'll bump into a Canuck and a guy in short pants!
 

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Premium Member 2013 SLK250
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2,387 Posts
WOW what have I learned here.

1. I must lose weight as it cost me gas mileage because my weight of a few pounds.

2. Do not have a tank low as I can get trash at the bottom.

3. Only buy what I will use today, do not want to have old gas.

4. Gas in storage tank needs to be colder than the air temp so when it heats up I will have more gas as it increases in sizes at a hotter temp.

5. Do not buy more than need as the price might go down.

6. Fill to the top because it might go up.

7. Must shake the car all the time to keep the gas mixed up.

Did I miss something? LOL
 

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My SLK only get out of the garage on the weekends, and then it's just cruising around town. A full tank of gas lasts a LONG time! I fill it up when it gets to 1/4 tank, as I also think the fuel pump likes that better. I won't put 1000 miles on it in a year.

Now my company truck (GMC) gets driven 300 miles a day, so I fill it every morning. I also run it down to 1/8 tank, but it doesn't seem to mind. I run my company vehicles about 200K then trade them off. Never had a fuel pump issue either.
 

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Premium Member
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No Coffee . . . but will a beer do???

Gas up in the morning . . . the "colder/cooler" the gas the more real gas per volume. Gas expands as it warms, so you get "less" when it is warmer. Gas up at or near a 1/2 tank . . . when you open the tank, vapors escape, less vapor escapes at 1/2 tank than at 1/4 tank . . . so you save on gas. Change gas and air filters often . . . they are the only thing between either dirty gas or dirty air getting into the engine -- inexpensive insurance. Always "gas up" in the same manner . . . I run the nozzle at "high" till it clicks, then "slow" till it clicks . . . and I reset my trip meter at every gas up (unless on a trip that I am monitoring) . . . I always divide out the gas/miles to get a MPG . . . then consider my driving to see if it is reasonable. You may often be able to know that "something" is not right if your MPG drops. And yes, I jump up and down on the trunk a few times to mix the new gas with the old . . . it goes with driving a SLK . . . :burnout:
 

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I don't want to call you guys paranoid but dayum. Lol.

I always fill up with 91 (highest they offer here). I try to fill up at a Chevron or Shell but I will take any gas station if I need gas and neither of those are nearby.

I typically fill up when at 1/4 tank because I can't be bothered to run to the gas station every-time I drive the car for an hour.

Theres times when I fill up gas when im 3/4 full already -> Going to Vegas or an SLKWorld run.

There's times when I forget to fill up with gas and my gas light is on and theses no gas station nearby -> SLKWorld run :p

I honestly don't think it makes any difference which way you do it, just don't let the car run out of gas, don't let gas sit for excessive periods of time: 4-6 months, don't fill up with diesel :)
 

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don't fill up with diesel :)
Best advice yet on this thread.

Can you fill up an SLK with diesel in the US? You can't over here as the diesel pump nozzle is deliberately made larger than the petrol one and therefore can't fit into the filler hole.

Mind you, it's possible to put petrol in a diesel filler, so I have a special cap on the fuel filler of our diesel 4x4 that can only be removed by a diesel pump nozzle.
 

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Premium Member 2013 SLK250
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2,387 Posts
I don't want to call you guys paranoid but dayum. Lol.

I always fill up with 91 (highest they offer here). I try to fill up at a Chevron or Shell but I will take any gas station if I need gas and neither of those are nearby.

I typically fill up when at 1/4 tank because I can't be bothered to run to the gas station every-time I drive the car for an hour.

Theres times when I fill up gas when im 3/4 full already -> Going to Vegas or an SLKWorld run.

There's times when I forget to fill up with gas and my gas light is on and theses no gas station nearby -> SLKWorld run :p

I honestly don't think it makes any difference which way you do it, just don't let the car run out of gas, don't let gas sit for excessive periods of time: 4-6 months, don't fill up with diesel :)

Yes, I am with you on this. This gas question is the same as which came first the chicken or the egg. :Beer:
 
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