reserve fuel
#21
Drifting
#22
Le Mans Master
A different application (gas station in tank pumps), but for a while I was an engineer at a pump company that made them and the flow of gas through the pump was what cooled it, not just being submersed.
I have also had external electric fuel pumps. Holley made them for a long time. Never had a problem with them either.
I have also had external electric fuel pumps. Holley made them for a long time. Never had a problem with them either.
#23
Racer
Well, I ran mine that low prior to installing a new fuel pump to support my blower set up. For normal day to day operation, I agree with you.
#24
Drifting
Ok, two questions...
First, how many gallons in the tank does it take to cover the pump? Reserve is 12L, call it 3.2 gallons, and 1/4-tank is 4.5 gallons, only about 5 quarts difference. I usually start planning the next gas stop at 1/4, but around town that's only about a 20-25 mile window.
Second, how hot is the pump designed to run anyway? I'm thinking 100+ day in Phoenix, exhaust pipes running right past the tanks...
I also find myself wondering how much early filling helps with the dregs. Seems like the dregs don't stop building up because you fill the tank more often: eventually the dregs will accumulate to whatever arbitrary fill-up point you select. The fact that there's no easily-replaceable fuel filter in the system is also a bit disturbing.
First, how many gallons in the tank does it take to cover the pump? Reserve is 12L, call it 3.2 gallons, and 1/4-tank is 4.5 gallons, only about 5 quarts difference. I usually start planning the next gas stop at 1/4, but around town that's only about a 20-25 mile window.
Second, how hot is the pump designed to run anyway? I'm thinking 100+ day in Phoenix, exhaust pipes running right past the tanks...
I also find myself wondering how much early filling helps with the dregs. Seems like the dregs don't stop building up because you fill the tank more often: eventually the dregs will accumulate to whatever arbitrary fill-up point you select. The fact that there's no easily-replaceable fuel filter in the system is also a bit disturbing.
#25
Drifting
Let's leave the design of the equipment to the engineers. (I'm an engineer in the nuclear industry). The key issue is NPSH (net positive suction head) for the pump which is relationship of the level, specific gravity and temperature of the fluid. Last of the considerations is how hot the pump is going to operate at. Fuel filters are relied upon for any considerations of "crud" in the system. Pumping systems are typically designed well within any normal considerations >150 degF.
#26
True story. My son was always running the tank in his Camaro to E before filling up. And I kept telling him that wasn't a good thing to do, that his fuel pump was eventually going to fail if he kept doing that. Well, guess what? I had the (sort of) pleasure of telling him "I told you so." Of course, he didn't like hearing that. But he didn't like having to pay for the R&R even more. Lesson learned. The hard way.
Last edited by thisMSGgood4me; 08-01-2014 at 11:19 PM.
#27
Drifting
I usually start looking for a Chevron station when the tank gets down to half-full. That gives me 1/4 tank to find Chevron specifically. Sometimes the price break can be significant on long (cross-country) trips--up to 30 cents per gallon difference in some places.
I think the 'half-tank practice' is good for keeping the pump cool and allowing me a better chance to shop prices. Locally, it's 12 cents a gallon merely for stopping at a different Chevron on the same route if I can wait that long.
I think the 'half-tank practice' is good for keeping the pump cool and allowing me a better chance to shop prices. Locally, it's 12 cents a gallon merely for stopping at a different Chevron on the same route if I can wait that long.
#28
Melting Slicks
Had a wife years ago who was seemingly incapable of putting gas in a car. Was always leaving me with a car with the guage on "E" or calling me 'cause she ran out of gas. I explained to her many, many times how hard on the fuel system and the engine this behavior was but, to no avail. Finally, one night she called me late at night to say I needed to come pick her up because my "stupid '55 Chevy (with the L88 spec 427 big block)" had the audacity to run out of gas on her. I picked her up, but it was too late to get gas anywhere (many years ago). I told her that it would have to sit there over night and woe be unto her if anything happened to it!!!!
The next morning, when she said let's go get your car.....I handed her a gas can and her coat and said, "You can't be bothered to put gas in the cars when they need it, here is what I have to do when you pull this stunt and I get stuck somewhere before I can get gas." She asked if I was going to drive her and I said, "No. You created this situation and you are going to walk your happy a$$ down there, fill up the can on the way and bring my hot rod home!!!"
It was hard for me to not fold and make her do it, but she never ran out of gas again!!!! She also didn't talk to me for about three days!! I guess between the two, some would call that a win/win situation.
She took me much more seriously about taking care of the cars after that as well.
DSTURBD
The next morning, when she said let's go get your car.....I handed her a gas can and her coat and said, "You can't be bothered to put gas in the cars when they need it, here is what I have to do when you pull this stunt and I get stuck somewhere before I can get gas." She asked if I was going to drive her and I said, "No. You created this situation and you are going to walk your happy a$$ down there, fill up the can on the way and bring my hot rod home!!!"
It was hard for me to not fold and make her do it, but she never ran out of gas again!!!! She also didn't talk to me for about three days!! I guess between the two, some would call that a win/win situation.
She took me much more seriously about taking care of the cars after that as well.
DSTURBD
Last edited by DSTURBD; 08-02-2014 at 01:11 AM.
#29
Melting Slicks
That was kind of my point: this whole meme of "don't let it get below X gallons or it'll hurt the fuel system/pump/whatever" is based on a bunch of hand-waving and zero actual evidence about how the critical bits were designed to work.
#30
Melting Slicks
But arguments based on equipment longevity are much less convincing. Seriously, does anyone here have any clue what temperature the pump actually operates at or how it varies with fuel level? Or any hard data showing how that variation correlates with pump life? Show me the numbers and I'll eat the crow.
#31
Le Mans Master
#32
Instructor
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Your half-full tank is a 9-gallon air-cavity resonator.
If the pump requires a certain amount of gas covering it to cool it, a competent engineer would put the reserve limit above that point. If you want to imply that the C5 design engineers were incompetent, be my guest...just let me get out of the splash zone first.
If the pump requires a certain amount of gas covering it to cool it, a competent engineer would put the reserve limit above that point. If you want to imply that the C5 design engineers were incompetent, be my guest...just let me get out of the splash zone first.
Personally never having seen the insides of a C5 tank, I'm just asking what that level is. My ears tell me it is higher than 1/4 full. I also only see pumps failing after 10 years or more due to this, so who's to say it the pumps would last much longer anyways. I look at it as a preventive maintenance kind of thing.
#33
Melting Slicks
Not incompetent as I have noticed all makes and models have this same issue. If you are going to have an in tank pump, then no matter how you do it, the pump is going to become uncovered at some point.
Personally never having seen the insides of a C5 tank, I'm just asking what that level is. My ears tell me it is higher than 1/4 full. I also only see pumps failing after 10 years or more due to this, so who's to say if the pumps would last much longer anyways. I look at it as a preventive maintenance kind of thing.
Personally never having seen the insides of a C5 tank, I'm just asking what that level is. My ears tell me it is higher than 1/4 full. I also only see pumps failing after 10 years or more due to this, so who's to say if the pumps would last much longer anyways. I look at it as a preventive maintenance kind of thing.
There's probably some critical internal part that gets corroded from being force-fed Techron.
#34
Team Owner
That "suck dregs" argument get's me laughing every time. I hear it from those who haven't actually seen or worked on a C5 fuel tank pump. For those who don't know the fuel pump has a large white filter element that actually rests ON the VERY BOTTOM of the tank.... in essence pulling fuel from the bottom to start with... ALL THE TIME!
#36
Not incompetent as I have noticed all makes and models have this same issue. If you are going to have an in tank pump, then no matter how you do it, the pump is going to become uncovered at some point.
Personally never having seen the insides of a C5 tank, I'm just asking what that level is. My ears tell me it is higher than 1/4 full. I also only see pumps failing after 10 years or more due to this, so who's to say it the pumps would last much longer anyways. I look at it as a preventive maintenance kind of thing.
Personally never having seen the insides of a C5 tank, I'm just asking what that level is. My ears tell me it is higher than 1/4 full. I also only see pumps failing after 10 years or more due to this, so who's to say it the pumps would last much longer anyways. I look at it as a preventive maintenance kind of thing.
#37
Instructor
Member Since: Mar 2014
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So there is no baffle to keep the sloshing to a minimum, and also to keep the fuel level float from jumpping around? I find that hard to believe. Every other tank I have actually seen in person had some sort of vertical baffling to prevent the float from swinging wildly. Not saying your wrong, but finding it odd that a vehicle designed to push the limits so to speak, wouldn't have baffles installed.
#38
Le Mans Master
Those that wish top argue the benefits of not running your tank low are going to hate some of us when we give 'em the old "I told ya'"
The fact is we may be wrong, but then, why gamble when the odds pretty much suck?
The fact is we may be wrong, but then, why gamble when the odds pretty much suck?
#39
Melting Slicks
#40
Team Owner
So there is no baffle to keep the sloshing to a minimum, and also to keep the fuel level float from jumpping around? I find that hard to believe. Every other tank I have actually seen in person had some sort of vertical baffling to prevent the float from swinging wildly. Not saying your wrong, but finding it odd that a vehicle designed to push the limits so to speak, wouldn't have baffles installed.
Btw, the float arms move straight up or down, and any sudden changes can be compensated for in the pcm software.