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Old 11-06-2019, 10:25 PM
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"Don't fill tank to max on hot days" - still true?


Does the advice about not filling a car tank to the max in hot weather still apply? (The fear being that heat-expanded gasoline would start oozing into the catalytic converter or outside the tank)


On a relevant note, by how much does gasoline expand when in a car that's getting heated up by hot sunshine? 5%? 10%?
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Old 11-06-2019, 10:35 PM
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Not the catalytic converter, but the evaporative emissions canister.
Just stop filling when the nozzle shuts off, and you will be fine.
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Old 11-07-2019, 12:18 AM
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Originally Posted by Velocity View Post
Does the advice about not filling a car tank to the max in hot weather still apply?
No. It never applied.

I don’t mean to be brusque, but this is not a real thing. On the other hand, asking “Is this a real thing?” as you’ve done, is a savvy question.

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Originally Posted by Velocity View Post
On a relevant note, by how much does gasoline expand when in a car that's getting heated up by hot sunshine? 5%? 10%?
Regardless of the heat source, each degree C (or K) increases the volume of gasoline by about 0.095%.

Really, this is not something to worry about when fueling your car. As long as you’re not pumping gas into a burning car, you’re fine.
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Old 11-07-2019, 06:43 AM
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Originally Posted by EdelweissPirate View Post
No. It never applied.

I don’t mean to be brusque, but this is not a real thing.

Really, this is not something to worry about when fueling your car. As long as you’re not pumping gas into a burning car, you’re fine.
It most definitely applies but only to the people out there who try and cram as much fuel into their tank as humanly possible.

For example the people who try and cram an extra $1.75 into their tank to try and get a round/even dollar amount and then drive a half mile home and park their car to bake in the heat of the day.

Cars nowadays are designed to capture the hydrocarbons from the fuel tank ventilation system and burn them off in the engine. If its overfilled with fuel it can cause all kinds of problems/trouble codes.

If you stop the first time the fuel nozzle stops then you're fine. But its surprising how many people don't know how sensitive the emissions controls are and how easy it is to overfill and cause problems.
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Old 11-07-2019, 07:00 AM
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It is a big problem but not in the way described in the OP.

There is an activated carbon canister in every car that absorbs the gasoline vapors as it evaporates from the tank. If you overfill (that is keep filling after the nozzle has clicked off) the gasoline goes and saturates this carbon canister. When this happens, you start getting the check engine light and you can’t pass the emissions inspection.

Although the activated carbon canister is not that expensive, it is located in a hard to reach place on many cars and replacing it is PITA / expensive.

I learned this the hard way. It was a 99 Camry and it was back in 2006. A hurricane was approaching and gas lines were forming and I overfilled just that once and paid for it later.
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Old 11-07-2019, 07:28 AM
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Originally Posted by Velocity View Post
Does the advice about not filling a car tank to the max in hot weather still apply? (The fear being that heat-expanded gasoline would start oozing into the catalytic converter or outside the tank)
The gas cap on my 1986 Dodge Charger had no lock, so I replaced it with an after-market one which did.

One warm day, I filled it up on the way to work. Around mid-day, I went out to the car to fetch something and saw that gas was dribbling out of the gas tank receptacle.

I don't know if the problem ever existed with factory gas caps.
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Old 11-07-2019, 07:50 AM
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I've always filled that way on every car I've every owned or used. Brim full every time. Never had an engine light, never had an emissions problem, never had an overflow problem.
I'm sceptical that it is a real, widespread problem.
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Old 11-07-2019, 07:59 AM
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It is advice with stations with above ground storage tanks to fill when it, and the tanks, are cool, thus fill in the early morning when the tanks were chilling all night and not in the afternoon when the sun heated them up. This way you are getting more gas for the money. But since most tanks are underground at a near constant temperature it doesn't make any difference.

As for the charcoal canister, it's OK to fill up when it's hot, as the gas is already at its most expanded, it will contract a bit when cool and less vapor pressure. It may be a issue the other way, fill up when cool, then leave the car in the hot sun all day will cause expansion of the fuel and perhaps problems.

The only thing that may have anything to do with the catalytic converter is if it is very hot out and lots of fuel vapors are created and displaced by the filling of the tank, which will on most cars exit out the fuel filler neck (Subaru PZEV's don't do this but still route the vapors through the canister, thus the partial zero emissions, zero fuel hydrocarbon emissions from fuel) . If the vapors are concentrated enough and hits a ignition source such as a overheated cat, well maybe boom. This is mainly mitigated with fuel pumps that include a vapor recovery system which most every one does now.
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Old 11-07-2019, 08:37 AM
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Originally Posted by beowulff View Post
Just stop filling when the nozzle shuts off, and you will be fine.
So in my van, more than I've noticed w previous vehicles, the gas seems to froth or bubble up and clicks the nozzle off very early. If I go slow (like the half depressed lever slow fill) I can put gobs more gas in. I presumed due to the speed gas sloshed out, if I stopped after the first click, I wouldn't be getting an actual full tank.

But I'm wrong?
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Old 11-07-2019, 08:39 AM
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Originally Posted by EdelweissPirate View Post
No. It never applied.

I don’t mean to be brusque, but this is not a real thing. On the other hand, asking “Is this a real thing?” as you’ve done, is a savvy question.



Regardless of the heat source, each degree C (or K) increases the volume of gasoline by about 0.095%.

Really, this is not something to worry about when fueling your car. As long as you’re not pumping gas into a burning car, you’re fine.
But fuel tanks do overflow from thermal expansion.

I used to drive a work truck with 2 separate fuel tanks. The forward one would be filled, then the rear tank. Since we were traveling a fair distance through heavy traffic, we started before dawn.
Later that day, after the temperature had risen (>40F, frequently), the unused tank would have fuel gurgle out through the cap.
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Old 11-07-2019, 10:58 AM
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Umm...I’d like to apologize for the content and especially the tone of my post above. All of it was off base.

I’d just come home from a long day at work and evidently so tired my brain turned off. Mea culpa.
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Old 11-07-2019, 11:21 AM
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Originally Posted by dontbesojumpy View Post
So in my van, more than I've noticed w previous vehicles, the gas seems to froth or bubble up and clicks the nozzle off very early. If I go slow (like the half depressed lever slow fill) I can put gobs more gas in. I presumed due to the speed gas sloshed out, if I stopped after the first click, I wouldn't be getting an actual full tank.

But I'm wrong?
What you're describing sounds like air getting mixed in with gas as it fills the tank. That's why you sometimes see old farts (like me) slamming a hip against the side of the car to "burp" the tank so we can fill it all the way.

I'm sure getting air mixed in with the gas was a concern at some point in automotive history. I'm not so sure that hip-checking the car to make the gas bubbles break made any difference.
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Old 11-07-2019, 11:31 AM
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How about temperature correction?

Warm gasoline would have less density and therefore less energy than cold gasoline. And gas station pumps don't correct for product temperature (or do they???). Is this an issue, are you getting less value on warm underground tanks compared to cooler underground tanks?
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Old 11-07-2019, 11:53 AM
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Originally Posted by Novelty Bobble View Post
I've always filled that way on every car I've every owned or used. Brim full every time. Never had an engine light, never had an emissions problem, never had an overflow problem.
I'm sceptical that it is a real, widespread problem.
I agree... having lived in hot areas for my entire life, I've NEVER heard this advice. Matter of fact, the only gas tank filling related advice concerning time of day is that you're better off filling up in the morning when the gasoline is cooler and denser, thereby giving you more gas for the same volume, and by extension for your money.

The real culprit is the topping off, not the ambient temperature.
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Old 11-07-2019, 12:26 PM
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Originally Posted by Annoyed View Post
Cars nowadays are designed to capture the hydrocarbons from the fuel tank ventilation system and burn them off in the engine. If its overfilled with fuel it can cause all kinds of problems/trouble codes.

If you stop the first time the fuel nozzle stops then you're fine. But its surprising how many people don't know how sensitive the emissions controls are and how easy it is to overfill and cause problems.
I do not find it surprising at all. I am probably a pretty typical car owner and I didn't know it. See below.

Quote:
Originally Posted by am77494 View Post
There is an activated carbon canister in every car that absorbs the gasoline vapors as it evaporates from the tank. If you overfill (that is keep filling after the nozzle has clicked off) the gasoline goes and saturates this carbon canister. When this happens, you start getting the check engine light and you can’t pass the emissions inspection.
I am not disputing this but Infiniti did not think it was important enough to mention in the owner's manual. Here is what they say about fueling:
Quote:
Do not attempt to top off the fuel tank after the fuel pump nozzle shuts off automatically. Continued refueling may cause fuel overflow, resulting in fuel spray and possibly a fire.
No mention of damage to the car.
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Last edited by CookingWithGas; 11-07-2019 at 12:26 PM.
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Old 11-07-2019, 12:58 PM
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Originally Posted by CookingWithGas View Post
No mention of damage to the car.
I understand your skepticism on my post and I really wish Tom (no longer with us) and Ray were around to give a definite answer.

Here’s the next best thing - cartalk forums. Please read through this post and decide for yourself - https://community.cartalk.com/t/what...r-filled/74965

Thanks
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Old 11-07-2019, 01:24 PM
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Quote:
Originally Posted by Novelty Bobble View Post
I've always filled that way on every car I've every owned or used. Brim full every time. Never had an engine light, never had an emissions problem, never had an overflow problem.
I'm sceptical that it is a real, widespread problem.
I've had similar experience in my 17 years of driving, and filling up, 5 different cars. I don't always top off, but have done so often and never had a problem. I always suspected it was a feature of American cars that is for some reason not present on European models, but a quick search suggests this isn't the case and European cars have had similar systems since 2000. So either we've been incredibly lucky, or it's a fairly unlikely thing to happen.

Cite, which seems to say short journeys can be a problem for the carbon filter. Which may tally with it being more prevalent in America, where society in general uses cars for short journeys more than in Europe. I hate to use my car for trips of less than a mile or two. preferring to walk or cycle or incorporating such errands into longer journeys.
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Old 11-07-2019, 01:44 PM
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How about temperature correction?

Warm gasoline would have less density and therefore less energy than cold gasoline. And gas station pumps don't correct for product temperature (or do they???). Is this an issue, are you getting less value on warm underground tanks compared to cooler underground tanks?
They certainly do in Canada. Every pump has a sticker saying "Volume Corrected to 15C."
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Old 11-07-2019, 02:23 PM
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They certainly do in Canada. Every pump has a sticker saying "Volume Corrected to 15C."
I thought that was corrected was for a different purpose and had nothing to do with actually varying the amount of gas pumped per unit based on temperature, but for checking a pump for accuracy in delivering what they say.
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Old 11-07-2019, 02:27 PM
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I've had similar experience in my 17 years of driving, and filling up, 5 different cars. I don't always top off, but have done so often and never had a problem. I always suspected it was a feature of American cars that is for some reason not present on European models, but a quick search suggests this isn't the case and European cars have had similar systems since 2000. So either we've been incredibly lucky, or it's a fairly unlikely thing to happen.
...
I had a car that if I pumped very slowly I could get another 4 gallons in it. I did that often as that 4 gallons ment 3 round trips before filling up instead of 2. I would typically do this then drive 1 mile home and the car sat overnight. Never has any known issue for the charcoal filter or any gas system related trouble. but I can't see how it wasn't soaked.

Perhaps it was also very long drives that allowed it to dry out enough after doing such a thing.
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Old 11-07-2019, 03:24 PM
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Originally Posted by am77494 View Post
I understand your skepticism on my post and I really wish Tom (no longer with us) and Ray were around to give a definite answer.

Here’s the next best thing - cartalk forums. Please read through this post and decide for yourself - https://community.cartalk.com/t/what...r-filled/74965

Thanks
I'm not skeptical, I was just explaining why the average guy (like me) doesn't know anything about this.
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Old 11-07-2019, 03:41 PM
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Really, this is not something to worry about when fueling your car. As long as you’re not pumping gas into a burning car, you’re fine.
If I had a new car for every time that's ever happened.
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Old 11-07-2019, 04:06 PM
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[QUOTEI've always filled that way on every car I've every owned or used. Brim full every time. Never had an engine light, never had an emissions problem, never had an overflow problem.
I'm sceptical that it is a real, widespread problem.][/QUOTE]

I'll second that post. I always top off the tank as far as possible, and have never had a problem. If I stopped pumping when the gas nozzle first clicks off, there would be two or three gallons of space left in the tank, and the capacity would be reduced to 11 gallons from the published 14 gallons.

Maybe because I live out here in the PNW where it almost never gets to 90° F, this makes more sense here than back in St. Louis or some such hellhole.
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Old 11-08-2019, 12:22 PM
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I was a dealership mechanic for awhile. Every couple months I’d see a car with the charcoal EVAP canister flooded with raw fuel and we’d have to replace it. Not a common repair, but it definitely happens.
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Old 11-08-2019, 12:32 PM
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I drive almost 10 miles from the gas station home.

That uses over a half gallon from my Ford E250. (my best mpg in the city is 14.2). 16 mpg on Trips.

Overfilling isn't a concern because the extra gas is only briefly in there.

Last edited by aceplace57; 11-08-2019 at 12:33 PM.
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Old 11-08-2019, 03:39 PM
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Originally Posted by dontbesojumpy View Post
So in my van, more than I've noticed w previous vehicles, the gas seems to froth or bubble up and clicks the nozzle off very early. If I go slow (like the half depressed lever slow fill) I can put gobs more gas in.
Quote:
Originally Posted by kanicbird View Post
I had a car that if I pumped very slowly I could get another 4 gallons in it.
Quote:
Originally Posted by Daylate View Post
I'll second that post. I always top off the tank as far as possible, and have never had a problem. If I stopped pumping when the gas nozzle first clicks off, there would be two or three gallons of space left in the tank, and the capacity would be reduced to 11 gallons from the published 14 gallons.
Given this seemly common occurrence--that full-speed pumping causes the nozzle to click off apparently early--can someone illuminate on exactly what is happening? What is the mechanism that causes the pump to self-stop? I presumed it was when gas touched the end of the nozzle...but now that I'm saying it out loud, that seems absurd. What kind of sensor would be required, and where would it be located on the end of the nozzle?

If it's simply a case of air getting in the mixture, what would be the ideal procedure? Allow fast-fill until the premature shut off, then slow fill until the first additional shut-off and stop then?
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Old 11-08-2019, 04:00 PM
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There's a small air tub inside the nozzle. When gas backs up to the end of that tube, it changes the air pressure that is holding the lever open which shuts off. Note that this is usually purely mechanical.

Next up: how a flush valve works in a urinal.
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Old 11-08-2019, 04:47 PM
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I don't force every last drop into the tank. My dad did that and wasted a lot of time.

I get maybe another 3/4 gal (after the nozzle shuts off) in the tank. That's full enough.
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Old 11-08-2019, 05:09 PM
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Originally Posted by ftg View Post
There's a small air tub inside the nozzle. When gas backs up to the end of that tube, it changes the air pressure that is holding the lever open which shuts off. Note that this is usually purely mechanical.

Next up: how a flush valve works in a urinal.
The gas doesn't even have to touch the nozzle. An increase in back pressure will do it.

FWIW, I once filled my F350 to the brim early in the morning, and when I went out at lunch, diesel was leaking from the filler cap.
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