best fuel level to maintain

[Frank Thompson]

I use half tank of gasoline in my chevy 2014 pickup per month. Is it better to maintain it between full and half empty or between half empty and almost empty?

[dpb]

For what definition of "best", pray tell?

[Frank]

I've always understood that running empty could cause a problem as gunk may get into system. I usually fill my little SUV when half full and never go below a quarter tank.

[dpb]

The pump pickup is at the bottom, anyway... :)

[trader_4]

I haven't had one apart, but unless it follows a float down or similar, what you say is logical. The only advantage I see to not filling all the way is reduced weight, but that isn't going to make much difference in MPG.

[makolber]

in pump tanks are kept cooler when covered

m

[dpb]

On 08/04/2016 3:05 PM, [e-mail] wrote: ...

The pump motor sits in a well/depression that can't be pumped dry for that reason...at least on all those I've replaced and I presume they're all designed that way.

[Wade Garrett]

Less likely to get water from condensation when it's full- plus if the ball goes up, you're better off with a full tank.

[Ed Pawlowski]

More full is always better. Fuel systems are better sealed these days but condensation was always a consideration. Ethanol added helps in that regard too.

I usually fill at 1/8 to 1/4 but have to fill up every 5 or 6 days so nothing collects.

Fuel has been improved too with better additive packages and filtration. If you use cheap unbranded gas, use a top tier every few fillups and you will get some benefits.

[bob haller]

if you run your tank dry, run out of gas it can and does damage the fuel pumps located in the tank. that can cost 600 bucks and more to drop the tank and install new pump

the pumps use the gasoline to cool the pump.

[Dean Hoffman]

Above half in the off chance you need to get somewhere in a hurry with it.

[Meanie]

Much depends more on the season. In winter, more than half to avoid condensation which doesn't build up as much in the summer. Otherwise, I don't think it makes much of a difference.

Every car I've owned (all pre 2000 models) was driven until the low fuel indicator illuminated and I've never had a problem with pumps or anything fuel related. That was also done all year long regardless of weather here in Mich. I don't think it's as much of an issue as some would think.

[Joe]

E-10 gasoline phase separation is your enemy. Humidity, daily temperature swings and how well your fuel tank is sealed are big factors. Will phase separation occur in your trucks tank? No one here can actually tell you.

Some theorize that keeping the tank full is better, some say it doesn't matter. Some would suggest using ethanol-free gasoline. Some would suggest using an additive like Sta-Bil.

If phase separation occurs, how much will the repair costs be for your truck?

How luck do you feel?

[dpb]

On 08/05/2016 4:04 AM, Joe wrote: ...

...

Actual documented evidence of such over typical short durations between tank fillings?

I've a number of vehicles that get intermittent use that sometimes go several months and have never experienced such.

[dpb]

...

Of fresh (uncontaminated) fuel in a vehicle tank, that is, certainly it's possible owing to contamination in USTs and the like...

Well, let's see -- yeah, if I work out the volume of water entrained in the 10 gal of a half-empty 20 gal tank assuming 100% RH @ 60F and 1 atm., I get it's roughly 1.3E-5 gal. The roughly 0.5% by volume required for phase separation equates to 0.005 gal so fully saturated air if all condensed to water would be only about 0.25% of that required to cause phase separation.

I'm thinking it's a non-issue...

[Jake]

Why don't you google it?

As the OP stated, it all depends on humidity, daily temperature swings and how well the tank is sealed. Personally I wouldn't worry about it and if I did, I'd use ethanol free gas.

[dpb]

On 08/05/2016 1:56 PM, Jake wrote: ...

See the follow-up; the point was asking if OP had any evidence of it in a vehicle, _NOT_ in UST or thru deliberate or accidental introduction of water but by condensation.

I went ahead and did some calc's; it's essentially impossible starting from uncontaminated fuel to introduce sufficient water volume that way.

[Jake]

Thanks but I think I'll believe the real experts.

[Tekkie®]

[e-mail] posted for all of us...

Actually the fuel is circulated through the pump to cool it.

[dpb]

Well, I'm not positive they're really experts; the following white paper says they're using a factor of 10X too low for the solubility/phase separation point--0.05% vis a vis 0.5%. I'm inclined to believe the latter over the former as being "more expert".

Even if the former were correct, it's still only 2.5% of the saturation volume in 100% RH air if were to condense it all. I'd be willing to listen if somebody could recompute independently and show gross error in the above estimate.

If it were such a problem as the above reference claims, it'd be happening all over the US in such high numbers there'd be no way the issue couldn't be addressed. I think they're simply over-reacting to the possibilities of clean fuel contamination. _Getting_ contaminated fuel from a service station, otoh, does happen fairly regularly owing to water entrance into USTs by various mechanisms or other ways of introducing water in bulk into supplies. But starting with clean fuel in a vehicle tank from condensation? Nah, ain't agonna' happen...

(PDF DOC link to a readable white paper on the subject by vendor of prevention/mitigation systems for bulk suppliers)