Miles to empty on 2017 86?

[Dadhawk]

Originally Posted by Wondark

I think water and debris of some sort is going to get in there anyway. Postponing when it gets in your fuel mixture by not letting the tank get low doesn't seem like a fix for it.

Water is most likely to get in the fuel from condensation as anything else, particularly in metal tanks, so sitting less than full and cooling down on a humid day (overnight) is a big cause of this.

Note thought that anything less than full can allow this to happen. Still the fuel is pumped from the bottom of any fuel tank so water would typically go out first. Pilots of small aircraft for example test for this before every first flight of the day, and should before every flight by draining a small amount out of the lowest points in the system and visually inspecting for water.

This is the schematic for the fuel tank. Interesting there are two fuel senders (19 and 21) but one fuel pump (18). I didn't realize that.



Also, there is a good tear-down of the pump in a very old thread here.

It looks to keep the pump submerged you would have to keep your tank over half full.

I can only speak from experience, but unless there are indications not to (like traveling and not familiar with fuel availability, or during a fuel shortage like has happened recently) I pretty much never fill up my tank before I am below a quarter of a tank. I've had multiple cars go well over 200,000 miles and have only ever had to change out one fuel pump in all those miles. The car had over 200,000 miles on it at the time, and that failure was due to a faulty wire, not heat related.

Seems pretty foolish to engineer a part that needs to be fully submerged in a liquid it is slowly pumping out of its own environment.

[Tcoat]

Originally Posted by 8RZ

Gasoline is a solvent and cleaning agent. I remember a shop I worked at opened up the tank of a 70s Buick that had over 300k on the ticker; tank was surprisingly clean on the inside still.

Ya, I am not sure where everybody is buying all this gas full of water and debris but maybe they need too check out new stations. Over several classic car restorations (each with way more than 300K) I emptied and inspected the insides of tanks and never found a single thing of concern. The pump is going to suck it all out no matter how full the tank is. That is why there are filters on the lines.

[Wondark]

Originally Posted by Dadhawk

Water is most likely to get in the fuel from condensation as anything else, particularly in metal tanks, so sitting less than full and cooling down on a humid day (overnight) is a big cause of this.

Note thought that anything less than full can allow this to happen. Still the fuel is pumped from the bottom of any fuel tank so water would typically go out first. Pilots of small aircraft for example test for this before every first flight of the day, and should before every flight by draining a small amount out of the lowest points in the system and visually inspecting for water.

This is the schematic for the fuel tank. Interesting there are two fuel senders (19 and 21) but one fuel pump (18). I didn't realize that.



Also, there is a good tear-down of the pump in a very old thread here.

It looks to keep the pump submerged you would have to keep your tank over half full.

I can only speak from experience, but unless there are indications not to (like traveling and not familiar with fuel availability, or during a fuel shortage like has happened recently) I pretty much never fill up my tank before I am below a quarter of a tank. I've had multiple cars go well over 200,000 miles and have only ever had to change out one fuel pump in all those miles. The car had over 200,000 miles on it at the time, and that failure was due to a faulty wire, not heat related.

Seems pretty foolish to engineer a part that needs to be fully submerged in a liquid it is slowly pumping out of its own environment.

I thought it was odd that it had that hump in the middle of the tank (obviously for more room for the shaft etc.. at the bottom) and wondered how they pumped the fuel from both sides.

Thanks for the diagram!

[billwot]

Originally Posted by Wondark

True story.



Would this have happened by running the fuel/water/debris mixture till it was low (or near empty)?

The water and other contaminants will always be at the bottom of the tank, full or empty.

[wheelhaus]

I fill up about once every two weeks, once a month in the summer when I'm on the bike a lot more. I prefer to run my tank low and refill with fresh gas, I don't want old gas staying in my tank for too long, so a full refill means less old gas each fillup. Constantly topping off means a certain percentage of old gas is repeatedly getting mixed back in and never gets used. Filters are there for a reason, and they are servicable. I'd also rather my filter catch these "boogers" instead of being worried about them sloshing around my water cup.

I understand the paranoia about running the tank low and sucking up contaminants. Two problems I see with this line of thinking... First it assumes that the tank doesnt slosh. This is a sports car, right? If it were a static tank that never moves, then sure... Secondly it assumes sediment isn't already being pulled up from a pump that picks up from the bottom of the tank in the first place...

[Overdrive]

Another matter though is that the fuel also pulls heat away from the running fuel pump so it doesn't overheat, acting as a coolant for the pump. If there is almost no fuel in the tank, the pump is a little less protected for however long that condition exists that it isn't submerged in fuel. Will one time or a few times do any real harm? No, but over time and habit, perhaps you'll find yourself replacing your pump sooner than intended.

As for "old gas", every time you fill up and introduce newer gas you're essentially refreshing the whole tank. Sure, there's some old in there, but it's all going away eventually, and it's not like the old stuff always stays in this one little corner continuing to go unused. Even then, consider also that the underground tanks at the stations where your refuel, much like your car's fuel tank, don't always go bone dry before they are refilled for your use. So the "fresh" gas you're pumping from that station's tank could very well be tainted with "old" by your definition. You never really know, and we just assume what's there is new and fresh. Ignorance is bliss.

Not saying don't do what you're doing, but know what risks may be there, and if you're willing to accept them and their possible effects, do as you like.

[billwot]

The "submerged in fuel cools the pump" is a myth. Yes, at start-up, the fuel will be somewhat cool, and yes, heat generated by the pump will be transferred to the cool liquid fuel.

But soon the pump temp and fuel temp come to equilibrium, and fuel is no longer able to absorb any more heat.. The fuel has no way to dissipate that absorbed heat, so its ability to absorb heat is limited to a short duration. Imagine what will happen to the engine coolant if there was no flow. The engine cooling system works because the heat-laden coolant flows to the radiator, where it is dissipated to atmosphere.

However, the flow of fuel THROUGH the pump does indeed cool the pump. Because the fuel is flowing, it not only absorb the heat, it CARRIES IT AWAY.

[PandaSPUR]

Originally Posted by wheelhaus

First it assumes that the tank doesnt slosh. This is a sports car, right?

^ This. I was thinking this while reading the entire thread.

Anything and everything in my trunk that isnt sitting directly on the carpet goes flying around, my dog gets bounced around, my girlfriend gets bounced around, my 200lb ass gets bounced around.

How the hell is some submerged dirt or water in the gas tank not going to get mixed up?

When you fill up is just a personal choice in my opinion. Whatever you feel comfortable with is when you should refill the tank.

In the city I like to keep it above half a tank since there are literally only five gas stations below central park, and only one of which are on the east side where I live. I could probably use up 1/4 a tank just driving 3 miles to that one station if theres traffic.

[humfrz]

Originally Posted by billwot

The "submerged in fuel cools the pump" is a myth. Yes, at start-up, the fuel will be somewhat cool, and yes, heat generated by the pump will be transferred to the cool liquid fuel.

But soon the pump temp and fuel temp come to equilibrium, and fuel is no longer able to absorb any more heat.. The fuel has no way to dissipate that absorbed heat, so its ability to absorb heat is limited to a short duration. Imagine what will happen to the engine coolant if there was no flow. The engine cooling system works because the heat-laden coolant flows to the radiator, where it is dissipated to atmosphere.

However, the flow of fuel THROUGH the pump does indeed cool the pump. Because the fuel is flowing, it not only absorb the heat, it CARRIES IT AWAY.

hmmmm........billwot ......are you saying that the little fuel pump is going to heat up 12 gallons of gasoline any measurable degree .....




humfrz

[Dadhawk]

As @Tcoat mentioned earlier, there is a big difference in running the car low on fuel and running the car out of fuel, in regards to the fuel pump.

In the end, the fuel pump is cooled and lubricated by the fuel running through it, not sitting around it. Yes, sitting in the fuel has some level of cooling effect, just as sitting in air would assuming the air is cooler than the pump.

Running the pump dry would have an impact on longevity, but as I mentioned above my experience has been that there is no negative impact on running the pump at lower fuel levels on an ongoing basis.

If you look at the schematic above, and at a picture of the fuel pump which sits vertically in the tank (below), you would have to keep your tank over half full to keep the pump fully submerged. And, the actual pump itself is surrounded by plastic, not in direct contact with the fuel.

[billwot]

Originally Posted by humfrz

hmmmm........billwot ......are you saying that the little fuel pump is going to heat up 12 gallons of gasoline any measurable degree .....




humfrz

Yup!

[billwot]

Originally Posted by Dadhawk

As @Tcoat mentioned earlier, there is a big difference in running the car low on fuel and running the car out of fuel, in regards to the fuel pump.

In the end, the fuel pump is cooled and lubricated by the fuel running through it, not sitting around it. Yes, sitting in the fuel has some level of cooling effect, just as sitting in air would assuming the air is cooler than the pump.

Running the pump dry would have an impact on longevity, but as I mentioned above my experience has been that there is no negative impact on running the pump at lower fuel levels on an ongoing basis.

If you look at the schematic above, and at a picture of the fuel pump which sits vertically in the tank (below), you would have to keep your tank over half full to keep the pump fully submerged. And, the actual pump itself is surrounded by plastic, not in direct contact with the fuel.

[Dadhawk]

Originally Posted by humfrz

hmmmm........billwot ......are you saying that the little fuel pump is going to heat up 12 gallons of gasoline any measurable degree .....

Originally Posted by billwot

Yup!

If it runs warm enough, for long enough, it will. Similar to how you can raise the temperature of a relatively large space with a 60 watt (non-LED) light bulb, or cook a cake with it in a small enclosed space like an Easy Bake Oven.

As long as the temp of the device remains warmer than the space around it heat will dissipate in order to equalize it.

I just don't think it runs warm enough to do have much of an impact as long as fuel is flowing through it which would be much more effective.

That doesn't mean car designers don't use that feature though. I've owned two Chevy Astros where in the design there was a circuit board (I believe it was the blower control circuit board) that had resistors on it that got very hot. GM designed the board to fit inside the very airflow it was controlling to keep it cool.

[humfrz]

Originally Posted by Dadhawk

If it runs warm enough, for long enough, it will. Similar to how you can raise the temperature of a relatively large space with a 60 watt (non-LED) light bulb, or cook a cake with it in a small enclosed space like an Easy Bake Oven.

As long as the temp of the device remains warmer than the space around it heat will dissipate in order to equalize it.

I just don't think it runs warm enough to do have much of an impact as long as fuel is flowing through it which would be much more effective.

That doesn't mean car designers don't use that feature though. I've owned two Chevy Astros where in the design there was a circuit board (I believe it was the blower control circuit board) that had resistors on it that got very hot. GM designed the board to fit inside the very airflow it was controlling to keep it cool.

Well, true, in a closed, insulated system.

However, the fuel tank is hardly closed (always has fuel running out of the system, as long as the engine is running; and it's certainly not insulated).

Note the keyword in my previous statement was "measurable", maybe I should have used "significant" .....


humfrz