Running low fuel levels

Mophead

Mophead

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Texas panhandle
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FJR1300
After following Uncle Phil's fuel pump dilemma and not wanting to detract from his thread I have always heard to not run the fuel level low because it is hard on the fuel pump.

So the question is does the fuel pump cool itself from fuel surrounding the pump OR does it cool from the fuel being pumped through the pump internally?

We see don't run the fuel level low on this forum, BMW motorcycle forums, Toyota Tundra forums, Chevy truck forums, and just about any motor forum you can imagine.

Before we had fuel pumps inside the tank (auto or MC) I don't remember any cautions on running low fuel level. Since fuel injection and pumps inside the tank we are now told to not use all the gas in the tank. If following that logic we would be filling up every 150 miles instead of doing 220/230 and then filling when closer to empty. More miles if on the ST supertankers.

Granted a fuel pump for carbs versus fuel injection has to work much harder to maintain FI pressures versus carb pressures. PSI versus drip drip drip. Reminds me of replacing small block chevy fuel pumps on the lower right side and using a hacksaw blade to keep the rod up in the block while installing the pump.

I have always run the tank low and not had fuel pump issues (jinx on the way for that statement). If it cooled from the outside wouldn't the fuel pump have cooling fins or something to make more contact with the liquid. As long as fuel is running through the pump, then cooling takes place regardless of how much fuel is in the tank.

This will probably be worse than a tire or oil thread so let 'er rip.
 
I believe it’s urban legend more than evidence based. To my knowledge no vehicle manufacturer routinely warns against operating the vehicle below a certain fuel level to prevent premature fuel pump failures. The fuel pickup isn’t directly on the bottom of the tank and using all the stated usable tank capacity does not suck the tank dry but leaves a small amount below the pick up level. As long as the pump has gas flow through it the pump is adequately cooled. On the ST1300 slightly more than 1 gallon remains when the range indicator starts blinking.

Finally, my anecdotal evidence is from my daughter’s use of the Honda Civic and Accord she drove through high school and college years. It was constantly on E or below if possible. It had 260,000 miles on the original pump when traded for first car she bought on her own.
 
I ran my ST1300 to 307 miles just last Wednesday. 7.06 gallons to fill. I've ran mine down to the point that it takes 6.7 6.8 6.9 gallons to fill so many times that I can't even count. The off brand fuel pump in my bike cost $18 delivered to my house off Ebay. The pump before it was under $40. I'm on pump number 3 right now. The original Honda pump went to 225,000 miles. The $40 pump went 137,000 miles. The third $18 pump has already gone 43,000 miles.

Believe what you want and do as you see fit. I say no difference or very small. At one time I researched this and some of the same pumps used inside the tank came factory outside the tank but I'm not searching for that info.
 
Mophead said:
So the question is does the fuel pump cool itself from fuel surrounding the pump OR does it cool from the fuel being pumped through the pump internally?
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Since the pump is immersed in the fuel that it pumps separating which fuel - what is inside the pump or what is surrounding the pump - is doing more cooling is probably impossible. I also suspect that ruminating on this question is futile.
 
The myth about not running around on empty most of time was started by us mechanics. My T bird would go through a pump on average in 60,000 miles,PIA to change as I had to drop the tank. When I made the habit to fill the tank when it got to a 1/4 tank the pump would last 100,000 miles. On fuel injected car systems the fuel gets warmed up by the fuel rail ,then sent back to the tank. Guess were the tank is in most cars, under the back seat close to the hot pavement on a summers day ,now run the A.C. in stop and go traffic ,it's going to get pretty dang warm under there. I believe thats when the pump gets over heated and wears out quicker than if you have a full tank of gas.
Now a Motorcycle is a total differant beast ,first tank has better air flow around it ,most of us avoid stop and go traffic. So even on low fuel levels ,that pump will not get as warm as in a car.
Like any electric motor ,fuel pumps have brushes which will wear out sooner or later.
 
On my 98 1100 that I used to commute 90 miles round trip, I always filled up after the 3rd day - so basically 270 miles... That's getting pretty low and I never had any problems with the fuel pump. (That ST had 101k miles when I sold it).
 
Well, I've had them fail at all sorts of mileage 'intervals' - so I don't know what that points to or away from. ;)
So far, three of the four ST1100s I ride have had fuel pump failures.
Two I replaced with a Quantum in the tank, one I replaced with a stocker.
One of the Quantum replacements had already had a stocker replacement before.
One of the four has 140,000+ miles on the stock fuel pump and it seems to be working fine.
I carry a spare fuel pump with me on longer trips cause a burnt child fears the fire ....
 
Uncle Phil said:
Well, I've had them fail at all sorts of mileage 'intervals' - so I don't know what that points to or away from. ;)
So far, three of the four ST1100s I ride have had fuel pump failures.
Click to expand...

Seems to me, after all the mileage you have on Honda 1100s, the clear answer would be to switch to a more reliable manufacturer of motorcycles.
It's not too late, not even for you. :rofl1:

(Most people who have hung around here will recognize my sarcasm. For those of you who don't, ...well, here it is on full display.)
 
I use to believe the urban myth too but that was before gasoline got so expensive. My lights come on frequently now and seems that its worse for wear. So far got 87K on the ST1100 and 256K on the Toyota all on the original fuel pumps.
 
It might be instructive to contact the manufacturer of these fuel pumps and ask them what the mtbf is for these units (mean time before failure), After they finish laughing for such an inquiry for a $60 fuel pump, ask the same question again.

Someone at Honda surely knows the answer to this question.
 
SMSW said:
Someone at Honda surely knows the answer to this question.
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But will they stop laughing long enough to answer?

The fuel pump ass'y (1100) from Honda is about $600. So I understand why guys are looking at after market.

I have an 1100 and live in Florida. It's warm here most of the year. I run my gas gauge to empty just about every tank. If I had wanted to tour and stop every 120 miles for gas, I would have bought a 1500 Valkyrie. Oh wait, I did. But I don't tour or ride any distance with it. It's capable but to really be suitable, it needs some farkles. One of the reasons I bought an ST1100 was for the fuel tank size. I have run the tank from full (squeezed in every oz I could) to below low level light flashing empty. Never had a problem. I have put over 7 gal. in a 7.4 tank, many many times.
 
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St-Gerard said:
Now a Motorcycle is a total differant beast ,first tank has better air flow around it ,most of us avoid stop and go traffic. So even on low fuel levels ,that pump will not get as warm as in a car.
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I doubt that the small quantity of fuel that is in an ST1300 fuel tank that is sitting directly on top of a 1300 cc internal combustion engine is cooler than the much larger quantity of fuel sitting in a car's fuel tank many feet away from that heat source. In addition to the much larger quantity of fuel that is exposed to the much larger surface area of a much larger fuel tank of a car that helps the fuel to better dissipate heat, it isn't exposed to any where near the same level of heat as fuel sitting directly on top of a running engine regardless of how hot the tarmac is.

I have never bought in to this heat theory. In fact, abnormal heat conditions excepted, I don't believe that normal heat levels plays much of a factor at all. The pump is lubricated by the fuel that is flowing through it, not surrounding it. Lack of fuel flow equals lack of lubricant, which equals pump damage. As long as there is a constant supply of liquid fuel there is pump lubrication.
 
Lubrication and pump cooling does not address electric motor cooling. Most motors need to be 75 degrees above ambient before performance degrades. Lower tank temps would be interesting from full to empty. Jmt
Which reminds me, I better put my spare in the sidecase before leaving Thursday....
 
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Andrew you maybe right about gas temps not having an effect on pump longevity, I wonder if the pumps in a car are momentarly running dry in corners at low fuel levels?
Personaly I prefer a full tank of gas over running on empty, I hate that worry will I make it to the next gas station.
 
Given this discussion is more impression based than fact based I avoid the issue by filling up at half-tank unless I'm done riding for awhile. Filling at half a tank helps me avoid sticker shock at the pumps. Heading back to the lair at the ned of the day on a half-tank allows me to pop the ST on the center stand and not risk a bilateral inguinal hernia. It's no fun.
 
Sadlsor said:
Seems to me, after all the mileage you have on Honda 1100s, the clear answer would be to switch to a more reliable manufacturer of motorcycles.
It's not too late, not even for you. :rofl1:

(Most people who have hung around here will recognize my sarcasm. For those of you who don't, ...well, here it is on full display.)
Click to expand...
Cheaper to replace the fuel pump - better the devil you know than the devil you don't know! :nanner1:
 
I would say there's always a gallon or so in my tank at all times, I have a 2.5 gallon aux tank so I'm pretty much ready for fuel at 275 to 300. I really cant imagine someone running it down to .5 gallons. I dont think the fuel gauge is accurate enough for that....not for me.
Bad filters and pumps running Under max loads is more likely causing the issue. Idk

I didn't think anyone would bite on the fuel return line........lol
 
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