Any potential issues filling to the brim?

Besides spillage at filling?

Wouldn't want to every fill up but say when going on a long trip. Fill until it's literally drops from overflowing the edge of the filler neck.

i would venture to say that is the way that the majority of members here fill up each and every time.

czeetah said:

Besides spillage at filling?
Wouldn't want to every fill up but say when going on a long trip. Fill until it's literally drops from overflowing the edge of the filler neck.

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No problem on a TDI, do it as often as you like.

DO NOT do this on a gasser, it can even throw a MIL/CEL on a gas powered car if the fuel expands back into the evaporative emissions system (which a TDI does NOT HAVE).

Bill

No issues whatsoever. I have been filling the tank this way for over 60,000 miles.

I do this If I'm leaving the station for a trip. but I dont if I an going home to park after fueling. The station I use is 1 mile from home, I have a slanted driveway and can get heat expansion during day while parked. Dont want to take the chance of dribbling on driveway, wasting the money I paid for fuel.

I've done this on my '03 ALH, with the vent guts removed, for roughly 200,000 miles. There is no evaporative canister on the diesel and as such there's nothing wrong with filling right to the neck, except one possibility -- expansion of fuel could cause a spill.

But -- this is very unlikely, as even a very short amount of driving (a few miles) will result in consumption of enough fuel to leave room for that expansion.

The thermal expansion coefficient of diesel (in general; remember that fuel is not an exact composition but rather a blend) is 0.00046 / degree F. Fuel coming out of a tank below the frost line is typically going to be at ~55F.

Remember that the tank is not insulated nor is the fill nozzle and such; as a result there will be a material amount of heating that takes place between the time you pump the fuel out of the tank and when you put the cap on. If it is 100F out and the fuel is at 55F there will be about a 2% shift in volume.

Probably half of that change in temperature will be absorbed before you cap the tank, so that reduces the expansion post installation of the cap to about 1%.

On a ~16 gallon fill that's about .15 gallons. Note that filling "to the brim" almost certainly does not exclude all air from the tank due to its shape, but in any event if you drive more than a few miles you will have consumed a sufficient amount of the fuel that an overflow cannot occur -- and that's under very extreme conditions.

jetlagmech said:

I do this If I'm leaving the station for a trip. but I dont if I an going home to park after fueling. The station I use is 1 mile from home, I have a slanted driveway and can get heat expansion during day while parked. Dont want to take the chance of dribbling on driveway, wasting the money I paid for fuel.

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Back into the driveway.......

As far as I see it, the only disadvantage to filling it all the way up (besides heat expansion) is that on the highway, you will probably have to pee before you need to refuel. It is more convenient for me when I can fill one tank and empty another at the same time. I believe there is such a thing as too much range per tank.

Have Fun!

Don

JSWTDI09 said:

As far as I see it, the only disadvantage to filling it all the way up (besides heat expansion) is that on the highway, you will probably have to pee before you need to refuel. It is more convenient for me when I can fill one tank and empty another at the same time. I believe there is such a thing as too much range per tank.

Have Fun!

Don

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You could always fill early!

When I think about the Passat's 800 mile range, that's basically an entire day of driving on a cross-country (or otherwise lengthy) road trip. I've found that I only have to fill on my way out in the morning after a night in a hotel, which is nice because it makes pee breaks shorter and more convenient along the way (no need to search our a decent station and add fuel).

^^^^
This is probably the most different thing about owning the TDI on trips. At my age, there is absolutely no question when driving all day that multiple breaks will be required, but they are free of considerations regarding fuel. Our last trip was to Chattanooga (@ 8 hours), and we've made it a number of times in the year we've owned the Passat. Drive down the 530 miles, then drive around while there. At the end of the visit...."Oh, right, better fuel up!" Almost an afterthought.......

Gave it a shot.

Couldn't really get it so full that it was above the misfuel guard.

But got to where it seemed like with the pump barely inserted past the gaurd it seemed to be wanting to spit back even after letting it settle and barely squeezing handle.

The only disadvantage I can think is the amount of time spent to get the fuel up to the brim. I follow Wayne Gerdes on cleanmpg.com when he does mpg tests. His cross-country trips in the Passat TDI and the Audi TDI's were fascinating to me, but he spends at least 1/2 hour filling up to the brim to be sure his test are as standardized as he can make them. I'm not willing to go to that extreme, but someone suggested waiting about 10 sec after the pump clicks off, then do it 3 more times and you're done. That's close enough to being full for me.

I fill as full as I can get to try and ensure I get good mpg calculations. I generally go to one of two fuel pumps, and they both let me put in about. 1.2 gallons after the initial stop before it gets really difficult to fuel.

jhinsc said:

The only disadvantage I can think is the amount of time spent to get the fuel up to the brim. I follow Wayne Gerdes on cleanmpg.com when he does mpg tests. His cross-country trips in the Passat TDI and the Audi TDI's were fascinating to me, but he spends at least 1/2 hour filling up to the brim to be sure his test are as standardized as he can make them. I'm not willing to go to that extreme, but someone suggested waiting about 10 sec after the pump clicks off, then do it 3 more times and you're done. That's close enough to being full for me.

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It takes an extra 60 seconds on the 2012 because there is no misfuel guard.

VeeDubTDI said:

It takes an extra 60 seconds on the 2012 because there is no misfuel guard.

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It's not like we are trying to set a world record or such. We just want to get an accurate era on our MPGs. One extra minute to complete the top off is more than I need on my car.

Do you guys remember the fellow that was all upset because he couldn't match the (then current) world record MPG in his own car? Now THAT was an unrealistic expectation.

Bill

jhinsc said:

The only disadvantage I can think is the amount of time spent to get the fuel up to the brim.

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Exactly, I fill it up, but I'm not going to spend more than a few minutes getting it close to the top. I have more important things to do in life then spend 20-30 minutes topping off my tank.

VeeDubTDI said:

It takes an extra 60 seconds on the 2012 because there is no misfuel guard.

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I don't think my misfueling guard is making it any more difficult to put fuel into the car.

VeeDubTDI said:

It takes an extra 60 seconds on the 2012 because there is no misfuel guard.

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Nor in my 2013....now. Really easy to remove that critter!

Having to forego two spectacular fuel price fill ups in rural TN because of wrong nozzles sealed it's fate.

If you are spending 20 or 30 minutes topping off, something is wrong. I have the guard and can do it easily in just a few minutes, no problem.

VeeDubTDI said:

It takes an extra 60 seconds on the 2012 because there is no misfuel guard.

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But are your SURE it's filled the brim? Why not just wait around 10 min to see if the fuel settles down into the tank? Accuracy has it's price! For me, close enough is good enough for me!

Yeah, if my fully calculations are off by 1MPG, I'm not going to lose any sleep.

jhinsc said:

But are your SURE it's filled the brim? Why not just wait around 10 min to see if the fuel settles down into the tank? Accuracy has it's price! For me, close enough is good enough for me!

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I'm sure. Absolutely sure. If the fuel drops after 10 minutes, it's because the engine is running.

40X40 said:

Do you guys remember the fellow that was all upset because he couldn't match the (then current) world record MPG in his own car? Now THAT was an unrealistic expectation.

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Feelings of failure and inadequacy must have been devastating. Equally difficult to match hybrid EPA ratings.

Biggest downside is the time wasted worrying about whether topped or not.

Biggest worry is the temptation to yell out "ROADTRIP" and set out to burn up that tank of fuel.

Second biggest worry is bladder capacity.

Never had a problem filling to the brim on the 2012.

Like others have said, if the intention is to keep driving until the tank gets empty, you'll either have a bladder that demands you'll stop for servicing or a stomach grumbling you do the same or perhaps both.

paramedick said:

Nor in my 2013....now. Really easy to remove that critter!

Having to forego two spectacular fuel price fill ups in rural TN because of wrong nozzles sealed it's fate.

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How does one remove said critter ? I hate it !

czeetah said:

Besides spillage at filling?
Wouldn't want to every fill up but say when going on a long trip. Fill until it's literally drops from overflowing the edge of the filler neck.

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No, there are really no issues.

But on the practical level, why would you want to do it?

So, say you are doing it for a long trip. The 14 Passat TDI holds 18.5 gal. So @ 43 mpg or better (- the Taylors went 84+ mpg 1,626 miles on a 12 Passat TDI) are you really going to go 795.5 miles? or use the FULL 18.5 gals ( @ whatever mpg you are posting) before fueling? To take that example to a yearly 15,000 miles per year conclusion: are you aiming to ONLY fuel 18 times instead of 18.86 , aka 19 times? Even IF you are, what is the BIG deal here?

Other threads asking when folks tend to fuel, indicate not many (aka, EXTREME minority) fuel when the low fuel lamp/buzzer comes on, let alone work on "fumes" portion of the tank.

I always fill my diesels to as full as I feel like. Sometimes, that's running down the side and other times, I don't even see the foam. I look at calculations over the long haul. The only issue i had over the years was on the beetle. If I got it to full, it would always leak some down the side of the car.

ruking said:

But on the practical level, why would you want to do it?

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I'd bet more people here do it out of OCD compulsions than anything else. Also, people want the most accurate calcs on their mileage too. The only way you can ensure that happens is to fill up to the same exact level every single time.

pparks1 said:

I'd bet more people here do it out of OCD compulsions than anything else. Also, people want the most accurate calcs on their mileage too. The only way you can ensure that happens is to fill up to the same exact level every single time.

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Yes, I would agree. The most accurate would be to run out of fuel completely and then refill !! The mileage would be as accurate as it could be, aka no more forward motion.

I have almost always have done and continued to do the first click off. The difference (on later models with the computer screen, for me, three separate computers) is almost always a bit lower, aka, not far off at all.

So for example, this morning I filled 13.4 gal /capacity of 15.6 gal (MB GLK 250 BT), aka, the low fuel indicator did NOT come on. It went on to post a 36.4 mpg, computer screen. Miles (487) /pen ink 13.4 gal calculation was 36.3 mpg.

So in that sense, what really does it matter 15.6 gal - 13.4 gal @ 36.3 mpg still gives me 79.86 miles???? This of course probably does not include the fuel in the fuel pump.