Fuel Cell/Fuel Level

[MBillings]

I need some coaching about how to determine the amount of fuel I have in my fuel cell. I don't want to run more fuel than necessary so I can keep the weight of my car to a minimum.

I have been told by some that I should use a wooden dowl and press it down through the foam to determine the fuel level. However, I'm concerned about damaging the foam. Comments?

Also, I may want to run a fuel level that does not keep all of the foam immersed. Is that an issue if I have a significant portion of the foam in the fuel cell is not saturated with fuel?

Thanks to the more "knowledgeable ones",

Mike

[Rick Kirchner]

Damaging the foam really doesn't matter, at worst it could set small bits adrift into the filter.

No issues with running the fuel low, other than pickup issues.

One of the guys on the site had a very small cell made for his autocross car - 1 or 2 gallons woudl do and allevaite any pickup problems.

[Dick R.]

The details depend on what your car and cell configuration allow.

In my case (85 Van Diemen RF-85) I inserted a length of pvc white water pipe in to the cell pushing it through the foam blocks and the cell bladder. I had to remove the metal filler neck first to get access and then replace it. Prior to inserting the pvc I drilled a lot of holes and also cemented a nicely rounded pvc pipe plug (female so it fit over the pipe). I made sure the bits and pieces of pvc were removed. The holes are to allow fuel to enter and exit the pipe freely. Since I don't have straight access for a dowel, I use a length of black fuel hose which has been calibrated by adding one gallon of gas at a time and then using tyraps as the markings. I chose black fuel hose because it shows the wet fuel better than any other color plus I knew fuel hose would tolerate the fuel. I verified that the pvc would hold up with a few days of soaking in gas. FYI after about 18 years of pump gas it was still fine when I recently replaced the foam.

I think the pvc pipe is thinner than the normal schedule 40 . . . maybe the thinner type used for yard sprinkler systems.

FYI I found out the foam had died when I went to check fuel level and my dipstick tube was gone . . . with no support from the foam the tube fell to the bottom of the cell. I simply replaced the foam and reassembled the system (easier said than done).

Also, my cell normally has about 2 gallons of Exxon premium unleaded in it after an event. Before event depends on number of runs and drivers. Generally about 3 gallons because I'm a worry wort. For out of town multi-day events I bring gas cans to add gas as needed between days.

I run a "take apart" glass fuel filter between the mechanical pump and the carb. FYI the dead foam never got into the filter. I got lucky. The filter is carefully tywrapped to the chassis. I would not run glass with a road race car by the way.

Dick
CM 85

[azjc]

Foam in my cell is in 3 pieces, in other words each piece takes up a 1/3rd of the cell. My fuel filler neck is such that I could insert a fuel resistant hose that is about 1" ID between 2 pieces of foam from the top to the bottom of the cell. It is at an angle and I can't get a straight shot down the tube or my filler neck so I use a small diameter wooden dowel that is flexible and marked for each gal. to check fuel level. I "calibrated" my dowel by filling the cell gal by gal when it was out of the car.... I then emptied the cell when in the car by pumping all the fuel I could out of the cell and refilling again to see how close the marks were. They are very close, I can pump out just about all the fuel out through the filler neck.

As for running and using the fuel pickup (I have a real nice surge tank).... I can run down to the last 1/2 gal, maybe a bit more. Most of my sessions are about 15 min and I found that I use about 1.6 gal per session. So, to play it safe I run about 2.5 gal in the cell most of the time. Except our Sunday Main event, it is usually more like 20 min so I start with 3 gal and use close to 2 gal. I'm not too worried about 6 pounds of fuel, by my scales I'm 1220 pounds with me and 3 gal of fuel on board. But I'm not running SCCA so impound is not an issue... we trust each other enough to not worry about it.

I've only run out of fuel once, but that was because I forgot to add before the first session on a Sunday .

[rickb99]

...Also, I may want to run a fuel level that does not keep all of the foam immersed. Is that an issue if I have a significant portion of the foam in the fuel cell is not saturated with fuel? Mike

NOT at all while you're racing. But be advised.. When in storage for long term or over the winter, most cell manufacturers suggest draining completely and let the foam dry out. Will last longer.

Damaging the foam really doesn't matter, at worst it could set small bits adrift into the filter......

LOL, Rick

In our rather 'aged' Reynard cell, one of those 'small bits' ended up in the inlet side of the fuel filter and slowed the flow enough to cause sputtering and a high speed miss on the straight during Jeff's last race of 2008 on the last 4 laps. Not a good way to end the season.. sigh.

[Steve Demeter]

I run a "take apart" glass fuel filter between the mechanical pump

Dick, Get someone to machine up a stainless "tube" to replace the glass one in the filter. they do break as I once learned the hard way.

[rickb99]

I run a "take apart" glass fuel filter between the mechanical pump

Dick, Get someone to machine up a stainless "tube" to replace the glass one in the filter. [FONT=Monaco]they do break[/FONT] as I once learned the hard way.

After our 'plug up' from a piece of foam I purchased one of those. But that's exactly why I never installed it.

Good idea on replacing the glass. You get the extra flow area for fuel without the breakage to worry about.

[Dick R.]

I run a "take apart" glass fuel filter between the mechanical pump

Dick, Get someone to machine up a stainless "tube" to replace the glass one in the filter. they do break as I once learned the hard way.

Good idea but that does negate the reason for the glass . . . being able to see how dirty it is. For autocrossing any extra flow is not an issue . . . full throttle bursts are very short. For road racing I would probably use a translucent plastic filter.

Note that I tywrap both ends of the filter to reduce the chance of either end cap loosening.

Dick

[formulasuper]

Good idea but that does negate the reason for the glass . . . being able to see how dirty it is. For autocrossing any extra flow is not an issue . . . full throttle bursts are very short. For road racing I would probably use a translucent plastic filter.

Note that I tywrap both ends of the filter to reduce the chance of either end cap loosening.

Dick

You can buy metal take-a-part fuel filters about the same size & design as the glass ones. I use one about 1 1/2" diameter X 2 1/2" long & unscrew one end cap for cleaning every couple of weekends. Never found anything in it.

[na94]

I am not a fan of the dowel method as it can give false high readings after running. That and the foam can help wipe off the fuel, which evaporates right away and makes an accurate reading difficult to achieve.

The most reliable method is to bring a 12v pump and empty the fuel cell.

General rule is a gallon for 6 60 second runs. Add to that a gallon for slosh.

[stephen wilson]

You can actually measure the liquid head pressure. Attach an inches-of-water gauge to a rigid or semi-rigid piece of plastic tubing, and insert until it touches the bottom of the cell. you would have to make a chart of what pressure = what volume of fuel, easily done by measuring fixed increments as you fill the cell.

[Dick R.]

I am not a fan of the dowel method as it can give false high readings after running. That and the foam can help wipe off the fuel, which evaporates right away and makes an accurate reading difficult to achieve.

The most reliable method is to bring a 12v pump and empty the fuel cell.

General rule is a gallon for 6 60 second runs. Add to that a gallon for slosh.

FYI the dowel or fuel hose method needs a tube such as thin wall pvc pipe with lots of holes in it to work without the wiping problem. I pull the hose and let the gas evaporate off the hose. Then "dip" again to get an accurate reading. I need a flexible "dipstick" due to the filler angle on my "Swift copy" VD.

Dick

[RobLav]

On my VD's, I've always used a 1/2" by 1/4" stick, sanded all around the edges, to measure fuel without ever any difficulty in reading it. I had that stick marked for graduations every 1/2 gallon.

Ths Citation is different, since the foam seems to be a bit stronger in the ATL cell.

[TedV]

I run a "take apart" glass fuel filter between the mechanical pump

Dick, Get someone to machine up a stainless "tube" to replace the glass one in the filter. they do break as I once learned the hard way.

X2

the metal in them bend easy and seals wont stand some fuels. I rigged one of the glass ones before the pusher pump on my diesel autocross Scirocco. I always planed to redo it. I found time to redo it the night before an autocross when it sprung a leak. Bent metal, guess a cone found it and took a little bit before it finaly puked on me.

I have one of the metal inline filters on the CM ford from Pegasus or maybe the local hot rod shop.

[Dick R.]

X2

the metal in them bend easy and seals wont stand some fuels. I rigged one of the glass ones before the pusher pump on my diesel autocross Scirocco. I always planed to redo it. I found time to redo it the night before an autocross when it sprung a leak. Bent metal, guess a cone found it and took a little bit before it finaly puked on me.

I have one of the metal inline filters on the CM ford from Pegasus or maybe the local hot rod shop.

Now that I will have a brand new fuel cell from Eagle I may upgrade to either a relatively large translucent plastic filter (if they exist for automotive versus lawn mower applications) or maybe a large metal filter on the suction side of a new mechanical pump. I found a wad of dead fuel cell foam in the inlet of the old mechanical pump (filter was on exit side . . . then!) Pump still pumped, however even with the foam. It looked like there is a fine mesh screen deep in the inlet so the foam never got to the inner workings.

Dick

[ahowe]

I am not a fan of the dowel method as it can give false high readings after running. That and the foam can help wipe off the fuel, which evaporates right away and makes an accurate reading difficult to achieve.

The most reliable method is to bring a 12v pump and empty the fuel cell.

General rule is a gallon for 6 60 second runs. Add to that a gallon for slosh.

This almost exactly matches my experience in Packwood this past weekend.

We burned 1.5 gallons in 9 runs and it was trying to experience pickup issues when I had approximately one gallon left in the tank. It didn't starve, but when I came off course I could hear the pitch of the pump had changed. It returned to normal on level ground while returning to grid. We added fuel to keep it above 1 gallon and it did not recur.

Andy

[Neil_Roberts]

If you have to run ballast, you may as well run ballast that does something. Fuel and batteries are the usual winners here. My preferred ballast configuration requires at least 5 pounds of fuel to meet the minimum weight. That's because I would much rather get disqualified at the scales than sputter through my last run or lap.

Like Dick R., I use a ventilated PVC pipe in the cell for a clear path to the bottom without shredding the foam. My fuel dipstick is a 1/8" steel rod with a washer at the bottom, held in place with bailing wire through a cross-drilled hole. Above the washer is an EPDM rubber seal and a stiff clear plastic or glass tube. At the top of the clear tube is another washer, a coil spring, and another washer and bailing wire through the steel rod. The clear tube and seal form a valve at the bottom of the dipstick that is held closed by the spring at the top.

When checking the fuel level, I will hold the clear tube, push down on the end of the rod with my thumb to open the valve, insert the dipstick, wait a couple of seconds, release my grip on the clear tube to close the valve, and lift out a column of fuel that is in between the tube and rod. That provides a very clear fuel level reading. Then that little bit of fuel goes back in the cell.

The rod is marked with a small notch every pound, a deeper notch every 5 pounds, and a V groove that runs all the way around the rod every 10 pounds. I prefer to mark the fuel level by weight rather than volume because it's easier to keep track of how much the car weighs. I store the dipstick in another PVC tube to keep it clean and protected.

In order to calibrate the fuel dipstick, I start with a full gas can sitting on a bathroom scale and an empty fuel cell. I will add a little bit of fuel, record the gas can weight and dipstick height measurement, and repeat until the cell is full. The result is a lot of X and Y data points at random intervals. I will then graph the data, calculate a best-fit equation through the data, and use that equation to determine the dipstick height at each pound of fuel.

Yes, I know, I have severely over-engineered the whole thing. But I'm able to finish a race very close to the minimum weight. After a National at Corpus Christi, I forgot to drive off-line and pick up junk on the tires during the in lap, so I went across the scales at exactly the minimum weight. Boy, did I ever get lucky that day!

[RussMcB]

Something else to consider - Many of our older cars have fuel cells not made to work with ethanol. I had a cell develop lots of pinhole leaks, and I'm pretty sure it was caused when street gas (w/ 10% Ethanol) sat in the cell for a couple of months.

[godwinmt]

On my vfr engined red devil I run a small 1 gallon foam filled fuel cell in the back of the left sidepod. Generally I fill it up to the top in the morning and that gets me through the event with a co-driver. Fuel pump is a small purolator electric pump, with a small plastic disposable inline filter up near the carbs. I check fuel level by pulling the cap off and spreading the two halves of the foam to see inside the tank.

Another thing you can consider to check the fuel level depending on your fuel cell is to do as FSAE does to a greater extent and have a pair of aluminum bungs welded into the side of the tank with a set of elbows on them with a clear chemical resistant tube between them similar to this setup used for a catch can to create a level indicator:

[brownslane]

On my vfr engined red devil I run a small 1 gallon foam filled fuel cell in the back of the left sidepod. Generally I fill it up to the top in the morning and that gets me through the event with a co-driver. Fuel pump is a small purolator electric pump, with a small plastic disposable inline filter up near the carbs. I check fuel level by pulling the cap off and spreading the two halves of the foam to see inside the tank.

Another thing you can consider to check the fuel level depending on your fuel cell is to do as FSAE does to a greater extent and have a pair of aluminum bungs welded into the side of the tank with a set of elbows on them with a clear chemical resistant tube between them similar to this setup used for a catch can to create a level indicator:

I would not recommend the above system. Why bother spending all the time, money and effort to build a safe system with containment cells, braided steel lines capable of withstanding hundreds of pounds of pressures, highly resistant to chafing, special fuel-resistant foams, etc....then negate the whole thing by building a plastic bung-and-hose arrangement that you could bust off with a couple of fingers. The above system would not pass tech in my area....and for good reason. Use a dip stick, keep your fuel safely and securely protected....all I see above is a great place to start a fire.

Cool looking and convenient, yes! Incredibly dangerous, absolutely!

[godwinmt]

plastic bung-and-hose arrangement that you could bust off with a couple of fingers.

Who said anything about plastic bung? I thought I explicitly stated aluminum bung/elbow? As I said, this is the style of setup that FSAE runs on hundreds of cars per year without any adverse affects. And FSAE runs multiple cars on track at the same time with controlled passing unlike any autox I know of. What's more dangerous? A chemical resistant plastic hose clamped securely between a pair of metal bungs on the fuel tank or a glass filter cage? I'd personally be much more skeptical about running a glass filter than this setup.

[Larry]

Why in the world would anyone play "What's more dangerous?" You have multiple alternatives--not just two, and there is NO reason to choose what you might think is the "least worse" of two. Instead of arguing the point, why not put your energy into finding a GOOD alternative.

Larry Oliver
International Racing Products

[nulrich]

Or you could just install a capacitive fuel level sender and a fuel gage! Fuel Safe will include the sender for very little additional cost on new cells, and many existing cells could add it to the existing cover plate, I imagine. You can either read it with a VDO style gage or (like we do) tie it into your data acquisition system. Isn't that useful on track, but is very handy in the pits and paddock.

Nathan

[brownslane]

Who said anything about plastic bung? I thought I explicitly stated aluminum bung/elbow? As I said, this is the style of setup that FSAE runs on hundreds of cars per year without any adverse affects. And FSAE runs multiple cars on track at the same time with controlled passing unlike any autox I know of. What's more dangerous? A chemical resistant plastic hose clamped securely between a pair of metal bungs on the fuel tank or a glass filter cage? I'd personally be much more skeptical about running a glass filter than this setup.

Godwinmt, you can choose to do whatever you want with the system. Just because someone else does it that way doesn't make it the best, or the safest!

Safety systems are designed to be a last-course protection for you should anything go wrong. Any external plumbing, made of anything is a weak point....Fuel cells and containment systems are designed to prevent any impacts from causing a fuel leak, and the potential life-threatening conflagration. Installation of a sight gauge, made of any material is a potential damage point and in fact, becomes the weakest and most vulnerable point in that system. Same as if you used plastic fuel line to deliver fuel to/from the tank, the fuel pump, etc.

And just because someone hasn't crashed a FSAE car and suffered such a failure does not mean the risk is not there.

I would think that, instead of copying someone else's flawed design, you could look at ways to improve the safety of the system, or perhaps copy some else's less-flawed design. Or design something yourself.

There are a hundred ways to build a fuel system...most all of them are safer than running a clear see-through hose outside of the otherwise protected system.

We just pump out the tank after every session (that way we accomodate any fuel that is not easily picked up...there always is a little) and then we refill with the appropriate fuel amount. Personally, I also have a dip stick (believe this, an undertaker's measuring stick) that I also dip the tank with. In my three cars I am lucky to be able to dip them all.

Sorry to have (obviously) offended you; that was not my intent. But I stand by my previous remark. And you know what they say about volunteering suggestions.....I wish you well.

[Joe_914]

Our fuel cell "gottcha's" were numerous on our 1st outing with the car. Call us crazy but our 1st event was Atlanta National Tour on Mothers Day.

Kinda funny as the car was a real Muther all weekend.

The foam was completely falling apart. We really had no idea how much fuel was in the cell. my last run of day teo I ran out of gas heading tot he sweeper. Car fell flat on it's nose and barely idled to the scales.

WhenI got the car home I tried my best to drain the tank and could not get all the fuel out. Decided to pull the tank. (Dang that was hard). Got the bladder out and with supply line open no gas would come out. I got a big bucket and poured the fuel out through the filler neck and got 2 gallons and a coffee can full of foam dust.

What a horrible experience getting all the shredding foam out of the filler hole. I could now pass the OB/GYN exam.

Anyway now the cell is empty of foam and spic and span clean. in line filter added, cel re-installed in the Autocross only car.

[brownslane]

And there is another lesson; fuel cell foam degrades with time. Much more quickly with ethanol-additives...so...if you use gas from any gas station.....!!! Do NOT leave this fuel in the cell for any length of time. The ethanol does two things; one, it is hyrgro-scopic (sp?) so it absorbs water and will contaminate fuel in as little as a couple of weeks, and two; the ethanol will destroy the fuel cell foam.

So what to do? Buy some two stroke oil (bike shop oil is best) and add it to the fuel in the cell. I use about 250 mls to a half tank (estimate) and I have found that the two stroke oil stabilizes the street fuel and the above problems will not happen, at least as quickly. No problem running the car with the oil in the fuel...for me, it would just burn off in the next practice session.

For winter storage, I always fill the fuel cell completely, add the whole bottle of two-stroke oil and I am good to go.

Why not just drain the tank and leave it empty? The fuel cell and the cell foam will dry out if left empty and the disintegration will occur more quickly.

FWIW.

Best,

[Evl]

You can actually measure the liquid head pressure. Attach an inches-of-water gauge to a rigid or semi-rigid piece of plastic tubing, and insert until it touches the bottom of the cell. you would have to make a chart of what pressure = what volume of fuel, easily done by measuring fixed increments as you fill the cell.

Anyone actually get this to work? Here's what I've done so far:

1. Bought a 0-15"H20 pressure gauge
2. Stuck it on the end of a metal tube
3. Found my tallest beer glass
4. Filled it with water
5. Stuck a measuring stick in the water, recorded 6.5" depth
6. Stuck pressure gauge/tube assembly in water, recorded 3.5" depth

Am I missing something? Should I not read 1"H20 for every inch I stick the tube in the water?

Just want to make sure I'm not overlooking something stupid before I send the gauge back as defective. My thoughts so far:

1. An air leak? Don't think so. When I first put it together, I had one, and the symptoms were that the pressure would rise up, then bleed down to zero. When you pulled the tube out of the water, the pressure would go negative until all the water came out, and it would go back to 0. It doesn't do that anymore not that I tightened everything up and used plumbers tape.
2. Tube too small? My tube has an OD of 3/16" and an ID of 0.09". (The path it has to take in my fuel cell is really tight.) There is definitely a lot of resistance if you try to blow through the tube, but I figure this is kinda like al electrical resistor/capacitor circuit. You don't need a high flow rate, the water will reach it's equilibrium point after a few seconds.
3. Too cold? I did try this initially after bringing in the box from the front step, but it's now been sitting on my desk all night, so the internals of the gauge should be nice and warm now, and I get the same results.
4. Hysteresis? It does take the gauge a little while to get from 0.2" to 0" after I remove it from the water. I've tried tapping the gauge to see if that would help it up past 3.5", but no luck, and 3" of hysteresis on a gauge with 1.5% advertised accuracy seems high!

Advice appreciated!

[john f]

I have this set up in my S2000. I have a tube mounted in the filler neck down to the bottom of the cell that is permanent. I purchased a $60 digital pressure gauge from Amazon and a blood pressure checker from Walgreen's. I use the millibar pressure setting as it seems to be easier to read? I calibrated the system by filling it 1 gallon at a time, pumping the tube with the bulb from the blood checker, and reading the pressure. You can not over-pressure the system because excess pressure relieves itself out the bottom of the tube. It works great. Repeatability seams to be very good and I have never run out of gas since installing it.

john f

[DaveW]

Anyone actually get this to work? Here's what I've done so far:

1. Bought a 0-15"H20 pressure gauge
2. Stuck it on the end of a metal tube
3. Found my tallest beer glass
4. Filled it with water
5. Stuck a measuring stick in the water, recorded 6.5" depth
6. Stuck pressure gauge/tube assembly in water, recorded 3.5" depth

Am I missing something? Should I not read 1"H20 for every inch I stick the tube in the water? ...
Advice appreciated!

Having the gauge at the top lets the water rise up 3" inside the tube until the air pressure in the tube balances the water pressure. Therefore you read 6.5 - 3 = 3.5" depth. The 3" of water in the tube subtracts from your reading. If the tube filled to 6.5", you would read zero. That is how the water levels (setup pads, etc.) that people use work - water seeks its own level.

So, IMO, the gauge is not defective. The setup you chose just won't work as long as the water can rise up the tube, and I don't see a way to avoid that.

[Evl]

Dave, thanks, I'll do like John's doing and pump the air out of the tube.

I guess it's a good thing I decided against being a physics major!