Pros and Cons of a Sumped Gas Tank?
01-10-2013, 02:45 AM
#1
Pros and Cons of a Sumped Gas Tank? I think I know most of the good versus bad but just wonderi g what others opinions are. I'm pretty much forced into using an external pump, so the upside would be if it was gravity fed out of the bottom of the tank instead of having to suck the fuel up and out of it, it should work better and probably last longer. The down side is if you get a leak in a line it would just all leak out. Changing the pump or filter would be messy to say the least too. So do the pros outweigh the cons, or should I just have the pump suck it out from the top of the tank?
01-10-2013, 04:50 AM
#3
Gotta watch the fuel level so you dont get air in the lines on hard launches or turns.....and since most sumped tanks run an external pumps, the pumps can overheat since the fuel is what keeps the pump cool. Both problems are solved by never going below 1/4 tank but I usually stay 1/2+ in mine unless Im on long trips.
01-10-2013, 05:19 AM
#4
If you have any type of hose coming off the tank than it is a pretty simple matter to clamp the line off when changing the pump/filter. You can also get valves if desired.
You have the same drainage issue even with a suck up and down as you call it. I have a standard tank pick up that comes out near the top then loops down to the pump level with the bottom of the tank. If I get a leak it will siphon the entire tank.
You have the same drainage issue even with a suck up and down as you call it. I have a standard tank pick up that comes out near the top then loops down to the pump level with the bottom of the tank. If I get a leak it will siphon the entire tank.
01-10-2013, 05:48 AM
#5
I'm thinking of running the plastic/nylon line, so probably don't want to clamp it off. But like others have said, I don't plan on changing filters or pumps very often and when I do, I'll just be quick about it. My main reason for doing it is there's no baffle in the tank and no way to put one in sand I don't want the low fuel level starvation problems. I think ill be alright since I'm not building a 9 second car or anything, just a daily driver truck with a stock 5.3. If my calculations are correct my Walbro 255 will flow. 07 gallons per second so it will take roughly 4 seconds to empty the sump on the bottom of the tank since it will hold a little over a quart of fuel, and since the tank is taller than it is wide from front to back, in 4 seconds the fuel should come back to the sump. At least that's my theory, I'll have to wait and see if it works out like I hope.
01-10-2013, 07:34 AM
#6
If you put a quart sized sump on the underside of the tank and feed it with a couple of 1/2 holes drilled through the bottom of the stocker, then your fuel system should be near bullet proof. IMO that is probably the best way you can do it. Putting some baffles in so the sloshing fuel is forced over the fill holes would be better yet, but depending on where you put the sump the baffles may not be needed.
Even with the bottom sump you will need some type of transition/bulkhead penetration from the sump to a filter to the nylon line. Weld an AN bung or on there and run a short section of push loc rubber hose up to the filter and from the filter out to a nylon transition piece. That will give you something to clamp should you ever need to pull the tank.
The web is full of guys who cut entire tanks in half to build baffles or put fuel cell access plates in the top of stock tanks to allow installation of internal surge tanks. There is always a way to modify a stock tank.
Even with the bottom sump you will need some type of transition/bulkhead penetration from the sump to a filter to the nylon line. Weld an AN bung or on there and run a short section of push loc rubber hose up to the filter and from the filter out to a nylon transition piece. That will give you something to clamp should you ever need to pull the tank.
The web is full of guys who cut entire tanks in half to build baffles or put fuel cell access plates in the top of stock tanks to allow installation of internal surge tanks. There is always a way to modify a stock tank.
Last edited by Pop N Wood; 01-10-2013 at 11:26 AM.
01-10-2013, 08:13 AM
#7
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Throwing out another idea. It is more complicated, but if you are really concerned, add a surge tank (~1 or 2 quarts) feeding the pump. With the main tank sump feeding the surge tank, you eliminate starvation problems. Then throw a valve on the tank for filter changes.
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01-10-2013, 09:46 PM
#8
One large con is the fact that your fuel pump, in all likelihood, cannot be situated below the sump pickup point. For some pumps, this isn't an issue, but I had to lose $200+ in order to find out a BG-220HR pump will NOT suck fuel uphill. For a DD, I certainly wouldn't use plastic hose. Which brings up another con. The exposed flex lines at the rear, the first thing to go in a rear-ender...
01-11-2013, 05:27 AM
#9
I think he is talking of using the nylon fuel line like all the new cars use. That stuff might be safer than hardline.
Also if he sumps the tank right he can have the fuel lines come out the front of the sump. That should help limit their exposure. It is also possible to put in a bulkhead fitting in the top of tank then run a fill tube down into the new sump. That shouldn't require massive tank surgery, gets the fuel lines up out of the way and still allows the external pump to be mounted low.
Also if he sumps the tank right he can have the fuel lines come out the front of the sump. That should help limit their exposure. It is also possible to put in a bulkhead fitting in the top of tank then run a fill tube down into the new sump. That shouldn't require massive tank surgery, gets the fuel lines up out of the way and still allows the external pump to be mounted low.
01-11-2013, 05:56 AM
#10
Yes, I'm planning on using the nylon hose but only for the flex points, the majority is hard line. As for getting the pump low enough, that's not a problem since the tank is in the cab, the pump will be 6 inches or so below it. I plan on hard lining it out of the sump so there will be no hoses in the cab. Shouldn't have to worry about the rear ender scenario either.
01-11-2013, 01:01 PM
#12
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If your talking about your current project I wouldn't even concern my self about having a baffle or surge tank, being how the tank is mounted vertically you aren't going to have much of a slosh issue.
01-11-2013, 07:19 PM
#14
Yes, it is my '71 C-10. The problem is the tank is wide, and when you get below 1/4 tank the gas sloshes side to side when going around corners. You can sometimes hear it! What I did on my blue '72 was bend the float arm up so the gauge showed empty when it was at a 1/4 tank. It worked, but I'm going to drive this one more so I want to be able to use more of the tank. Don't want to be filling it all the time. H
01-12-2013, 05:09 PM
#16
I went ahead and put the sump in the tank. Wasn't too hard, pretty straightforward. Now comes another question. Since I'm not using the original sender with the sock on the end to feed the pump, what kind of filter should I put ahead of the pump? Would a fuel filter for a carb'd application work since it's before the pump therefore no high pressure, or will it cause too much of a restriction? Also its going to be inches away from the pump, the pump wouldn't suck it apart would it? Anyone have any ideas on a better way?
01-13-2013, 10:48 AM
#20
Pump prefilters vary depending on the type of pump. Most manufactures recommend 100 micron prefilters for rotary vane pumps and 40 micron for gerotor pumps. Summit sells filters that use steel mesh screens in either 40 or 100 micron for a reasonable price. Most of those are for external pumps.
And yes, you want a low loss prefilter if possible.
And yes, you want a low loss prefilter if possible.