The Stovebolt Site Forums The Shop Area The Electrical Bay auxillary fuel tank electrics

If I was to install a secondary fuel tank on my 3600, what would I need for electrics/fuel delivery/gas guage? My F150 has two tanks with a switch to move from front to rear tank. I read in that manual that there are 3 pumps; two low pressure in-tank and one high pressure external for that vehicle's fuel injected system. My bolt has a carburated 350 with a mechanical fuel pump. So, 2 external high pressure electric pumps with a switch? And will that same switch allow the respective sending units to drive my guage? I was thinking I could go to the Ford dealership and buy that same switch... Suggestions, tips, comments?

High pressure fuel pumps are for fuel injection units. Do not use this with a normally aspirated carburetor, you will have gas blowing out all over. A typical carburetor only needs about four to six pounds of fuel pressure with a 3/8 inch fuel line. Your current mechanical pump will do just fine, no other pumps.

Your new fuel gauge sending unit must match up to your gauge. This is rated in resistance (Ohm) units. Check around, there are listings stating the Ohm rating for your '57 gauge. This must match for a correct fuel gauge reading.

You have two choices. You can run dual tanks as a single tank. Simply connect your fuel lines together through a T fitting. When the tank with a fuel gauge sending unit is empty, so is your other tank; behaves as a single tank.

Other choice is separated dual tanks, dual sending units, a fuel splitter and a single fuel gauge. Your fuel splitter is simply a Y connector with an internal valve; one tank or the other feeds fuel. A mechanical fuel splitter is much more reliable. Should an electric (solenoid) splitter go bad, you are out of luck if an "off" position is also a "fuel off" position. Marine part suppliers sell really nice brass mechanical fuel splitters, fit nice on a floorboard like above your starter button; you can switch positions with your foot.

You need a switch to change fuel sending units. This is simply an "on-off-on" type switch. Typically has three terminals on back. Tank one goes to an "on" terminal, tank two goes to the other "on" terminal, remaining third terminal goes to your fuel gauge. You can buy a kit which has both a fuel splitter and a matching switch for both the fuel splitter and your two sending units. Look around on the web, lot of kits out there with explanations how those work.

Easy to install, a no brainer. Routing your fuel lines and making connections is a tougher job.

Personally, I use a mechanical fuel valve splitter for reliability, nothing can go wrong.

Remember, only your low pressure mechanical pump, no other pumps.

Billyray

Billyray,
Did a search for "fuel splitter valves" and came up with not much. West Marine has one manual brass 3 way and that's it. Some stuff I did not comprehend either high tech avaition or part of modern VW fuel systems. No kits as you suggested. Can you give me any leads? Thanks, Don

You really only need one gauge. Run your ungauged tank til you run out, switch to the full gauged tank.

Don asks, "Can you give me any leads?"

Sure. First a scribbled diagram for you to look over. This diagram I scratched out will give you a good idea of what you need, even the "name" of the switch you need.

Dual Fuel System

Big image but fast loading. Scroll up and down.

Download my drawing then save it somewhere or simply print it.

An "SPDT" switch is simply a toggle switch or rocker switch which has 2 "on" positions. Some will have a middle "off" position. You can hook up 2 devices and turn on one or the other but not both. This is to switch between sending units.

A "DPDT" switch is 2 switches in one like having 2 SPDT switches in one box, single toggle or rocker works two switches inside, at the same time. This is to switch sending units and to switch an electric fuel valve.

An electric fuel valve usually has only one "hot" wire, then your usual ground wire. A device inside slides to one side when power is applied, spring pushes it to the other side when power is turned off. This switches between fuel tanks.

Study my diagram so what follows will make sense to you. Once you have a good mental image of what you need, then you can find parts on your own and save money.

I am splitting up posts to address each topic individually. More to come.

Billyray

SPDT switch and DPDT switch, these are found all over. Radio Shack is a good start. Ebay, by the hundreds. Auto Zone carries some varieties of these. Electronic surplus parts warehouses, used stuff, by the thousands. Cheap and easy to find.

You only need one switch, which depends on if you go with a mechanical fuel valve or an electric fuel valve.

SPDT - mechanical fuel valve
DPDT - electric fuel valve

Get you a nice looking dash mount switch, some lengths of wire, pinch terminals, good to go.

Billyray

Mechanical fuel valve, you can find these on Ebay in "boat parts". Also look at "marine parts" stores on the web. At Ebay, simply use "fuel valve" for a search, then click on "marine" or "boat" whichever Ebay provides on the left side. On the web, you will have to go right into web sites then search for this valve inside the store. Lots available, just have to search a bit in Ebay or inside an online marine parts store.

Electric fuel valve, well, just pick a truck brand and go to an authorized dealer on the web. Ford has a nice unit, single wire operation. GM, Dodge, have their units, just as nice. Best to go straight to a dealer, like Ford, then search inside their store "fuel valve" to get returns. You can buy directly online or pull a part number then order from Auto Zone, whatever. Easier to buy on the web.

Takes a bit of searching but you will find what you need. Just aggravating to have to sort through so many parts.

Billyray

Sending units. This is important. Old trucks often require a "30 Ohm" sending unit. There are a lot of variations on this. You will need to visit classic truck part stores on the web, find your FUEL GAUGE and discover if an "Ohm rating" is stated for the sending unit.

Then search one of those stores for a sending unit, factory style, correct for your truck, then discover if an "Ohm rating" is listed.

Once you discover the Ohm rating of your needed sending unit for your fuel gauge, then you can shop around. Look at "universal" fuel gauge sending units. Those come in different Ohm ratings and fit just about any tank. Easy to calibrate and install, piece of cake.

Remember, your sending unit Ohm rating MUST match your fuel gauge.

Billyray

Tanks, if you are to connect the fuel lines together for both tanks, a common feed which behaves like a single tank, your tanks must be level with each other.

An example is you hook together a "behind the seat" tank and a "under the rear frame tank", your seat tank is much higher and gas will drain into the lower rear frame tank. This tank will overflow.

An easy cure is a "one way check valve". This is a small device which looks like an inline fuel filter. Only allows gas to flow in one direction. You insert this in your lower tank fuel line with an arrow pointing to your fuel pump. Gas will only flow to your fuel pump, no gas can flow into your lower tank from the higher tank.

With a splitter fuel valve, this is NOT a problem. The valve itself keeps the tanks separated. No sweat.

For your small block Chevy engine, you only need the mechanical fuel pump down there on the block. No other fuel pump is needed.

Beyond safety issues, like good quality steel line or braided fuel line, your only critical part is a sending unit which matches your fuel gauge, no exceptions on this.

Keep this in mind, if an electric fuel valve fails, you will be stuck with only one tank or your fuel is completely shut off. This one tank will probably be your empty tank. A mechanical fuel valve, nothing can go wrong other than you forgetting to switch tanks then running out of gas in a bad neighborhood whereupon you will be carjacked and the bad guy will be really mad because he cannot start your truck.

To close, Don, you need to decide if to go a mechanical fuel valve or an electric fuel valve. SPDT switch for a mechanical valve, DPDT switch for an electric valve. Carefully find a matching fuel gauge sending unit for your factory gauge, grab yourself some wire, fuel line and fittings and enjoy having grease and rust in your eyeballs during installation.

Oh yeah, wiring diagrams are usually included with your sending unit and your electric fuel valve. No problem there.

Billyray

Forgot to add, Don, on those switches, use the diagram which comes with the switch, or use a Volt / Ohm meter, a low volt test lamp, whatever, so you will know what each terminal on the switch does.

My crayon diagram shows the typical but not all switches will hook up like I show. Play with your switches, safely, to figure out what is on, what is off and what happens when you flip the switch.

A serious CAUTION is never hook up a hot lead, 12 volt nor 6 volt, to neither your sending unit nor your fuel gauge. Both work by being connected to "ground". A positive hot wire accidentally hooked to a gauge or sender will ruin the unit.

Make sure your switch is correctly wired BEFORE you hook up the sending units and the gauge. Double check and triple check.

Billyray

Wow.......Billyray, you are a treasure trove of info....lots and lots and lots and lots of info!

Stuart

atomarc quips, "Billyray, you are a treasure trove of info....lots and lots and lots and lots of info!"

Nah, when I take to sipping whiskey, my jaws never quit flapping, except when my ornery wife whops me upside my head and tells me to shutup. She flaps her jaws a lot more than I do; can't hit a woman.

Billyray

What would be the pros and cons of using a 6v electric fuel pump that delivers 3-4 psi or 5-8 psi?

Tim asks, "What would be the pros and cons of using a 6v electric fuel pump that delivers 3-4 psi or 5-8 psi?"

This is like choosing between Marlene Dietrich and Marilyn Monroe. One is a raven haired beauty with smarts, the other is a blond headed beauty without a lick of sense. Nonetheless, both are capable of taking care of your needs.

Selection of a fuel pump is based upon demand and delivery; the higher your engine demand, the more a pump needs to deliver. Volume need is first, pressure need is second.

Here is contrast. You have a Chevy 216 with a tiny one barrel, you could use a child's squirt gun to service this engine just fine, even at full throttle. My girl's Corvette has dual quads sitting on top of velocity stacks. She needs a Chevron oil refinery behind her seat to keep enough gasoline flowing just at an idle.

For both an old tiny 216 and her modern 383, I would use a mechanical fuel pump producing 6 pounds of pressure or less, never more than 6 pounds. This hot rod Corvette of ours has a return line running from the carbs back to the fuel tank. A typical Edelbrock mechanical fuel pump delivers more gas to the carbs than what is really needed. Fuel pressure at her carbs is only about four to five pounds which is plenty. Difference is an Edelbrock fuel pump delivers a lot of gas but at a low pressure.

Here are some pros and cons between mechanical and electric pumps.

Both can deliver a high gas flow at a low pressure.

A mechanical pump delivers more gas as engine speed increases. An electric pump delivers the same amount of gas regardless of engine speed.

A mechanical pump has the power of the engine operating the pump. An electric pump has only the power of its internal motor or vibrating solenoid.

A mechanical pump will deliver more gas per pump stroke than will an electric pump.

A mechanical pump "sucks" gas from a tank more powerfully than does an electric pump.

A mechanical pump only quits when the engine quits. An electric pump quits when there is a loss of electricity, such as a blown fuse or internal short.

A mechanical pump will last over half a century. An electric pump lasts about five to ten years.

A mechanical pump is less expensive than an electric pump while all things are equal between the two pumps.

Personally, I only use mechanical pumps, always. A mechanical pump will almost never quit working for you. An electric pump will eventually quit working, without warning.

Billyray

Tim, some points on fuel pressure, not volume, just pressure.

A carburetor cannot tolerate over about 6 pounds of pressure. I am ignoring specialized racing carbs, let's just talk ordinary carbs.

Inside a carb is a tiny needle valve which opens and closes to allow gasoline in. This valve is connected to a "float" which rises and falls with the fuel level inside a "float bowl" internal to a carb. This is _exactly_ like the toilet in your house which has a valve attached to a float. Pressing down the gas pedal on your truck is just like pressing down the handle on your toilet and, oddly, same type of crap comes out the exhaust.

Whether a carburetor or a toilet, the fuel pressure or the water pressure must be kept below a certain pressure limit. When this pressure is exceeded, the valve blows apart and flow is constant, non-stop, your carburetor floods or your bathroom floods. Either leaves you stuck with a real mess, not sure which is worse to clean up.

For a typical carburetor, about 6 pounds is the maximum limit, 2 pounds is the minimum limit. A pressure of 4 pounds is Goldilocks just right. There are variations, but this is the general rule. While volume flow is good, pressure does not much matter. Gauge your need on much gas needs to be delivered to your carb, not how much pressure is needed.

This is an easy experiment any reader can enjoy in a just a few minutes. Pretend your toilet is a carburetor. Take the water tank lid off. Close the water valve down at the wall. Flush your toilet and watch the water in the tank. At first, a big burst of water will come out of the supply valve, then fall off to just a dribble, finally stopping. Your tank never will fill. Crack open your water valve just a tiny bit. Water will only dribble out of the valve, takes forever to fill your water tank. Open the valve all the way, tank fills up, no problem.

This is the difference between volume flow and pressure. Whether your toilet water valve at the wall is opened or closed, the water pressure remains the same. However, flow of water changes dramatically with valve changes; on or off, dribble or full flow.

Volume of flow is what counts, not the pressure.

Billyray

For modern electronic fuel injection, Tim, pressure does matter, very much so. Very high fuel pressure is needed, typically in a range of 30 to 50 pounds per square inch. Flow still must be good, but is not as important as a carburetor system.

Reason for this is fuel flows through a very tiny hole in an injector, a tiny hole like in a carburetor fuel jet, but even smaller.

Pressure must be high to "vaporize" the fuel upon leaving an injector. This is vapor versus liquid. Fuel injection requires a "mist" of fuel, a carburetor simply needs a liquid flow just like the toilet in your home.

Fuel injection units are designed to handle this type of high pressure, and must have high pressure. Pump this type of high pressure into a carburetor, it will explode sending your air cleaner punching through your hood then flying clean over the moon and will circle the Earth several times before coming down.

Only use I find for high pressure fuel pumps is building fuel injected exhaust flame throwers. My girl loves her flame throwers on her Corvette, gives her a feeling of great power over the boys at car shows.

Cops sure don't like flame throwers on cars; frustrates a cop to figure out what type of ticket to write for flame throwers, "Your honor, her car was spitting out flames. Don't know what violation this is, but this has to be a violation of some law."

A gas tank which has a fuel pump inside will almost always be a high pressure fuel pump. This is why I jumped on this pump in the tank thing for installing a second fuel tank. This is a sure bet of launching a carburetor air filter, if not over the moon then right on out to Mars.

Carburetor: low pressure high volume pump.
Fuel Injection: high pressure low volume pump.

Billyray, waiting for his air cleaner to return from space...

Billy Ray,

What is the required/recommended fuel flow for a one-barrel Rochester (1954 235, for example)?

Is the flow measured in gallons per minute?

tclederman asks, "What is the required/recommended fuel flow for a one-barrel Rochester (1954 235, for example)? Is the flow measured in gallons per minute?"

Any original equipment like mechanical fuel pump will work just fine. Get yourself a rebuilt, new, any brand, whatever, you will have no problems. Same is true for an electric fuel pump. Your fuel flow requirements are so little just about any type of fuel pump will work great. Shoot, you could sit a kid under the hood with a squirt gun loaded with gasoline and make a good ten miles before the kid becomes uncomfortably warm.

Don't fret over this, just get yourself a good quality fuel pump, preferably a mechanical type.

On gallons per minute, only applies to my girl's hot rod Corvette. I guesstimate she goes through high octane fuel at about 10 gallons per minute. At car shows, I have to follow behind with a Chevron big rig gas tanker to keep her in fuel. Lasts about one day, half a day if she is heavy on the flame thrower button.

Get yourself a good fuel pump, don't worry about the fuel flow. I would be more worried about dogs chasing after your truck to suck on your tailpipe to get high, modern day dogs are like that.

Billyray

So, both 3-4 psi and 5-8 psi 6v fuel pumps should work?

I might want to use an electric fuel pump (even though I appreciate your kind and clear recommendations to use a standard mechanical fuel pump).

I have asked the vendor of the two 6v pumps (in-line pumps - not in-the-tank umps) what the gpm flow rates are.

Tim asks, "So, both 3-4 psi and 5-8 psi 6v fuel pumps should work?
I might want to use an electric fuel pump...."

A pump at 3 to 8 psi will work perfect. I would be cautious at 8 psi, this is a bit on the high side for your carburetor. This high is usually for high performance gas guzzlers. An 8 psi will work fine but you will need to make sure all your connections are tight and your carb needs to be in good condition, freshly rebuilt is best.

Carter is your best electric fuel pump, both 6 and 12 volt. A Carter 6 volt delivers just under 6 psi which is great for your needs. Flow is around 70 gallons per hour which is a lot.

This is a super nice Carter 6 volt pump:

Carter Pump

A pump to avoid is a solid state electric fuel pump like the "Facet" brand name. Those are crap. Pressure is OK around 4 to 5 pounds, flow is moderate, around 30 gallons per hour. However, a solid state "electronic" fuel pump of this type has almost no suction power. If this pump is more than a foot above a tank, it will not self prime, just sits there rattling.

This what a Facet "electronic" type pump looks like:

Bad Pump

A cheap pump like this one above will leave you stranded roadside, sooner or later.

Go with a Carter electric pump, best on the market, very reliable, long life span. Worth the money with not having to worry about breaking down somewhere.

Billyray

Thanks, Billyray.

What about NAPA AFPE8011 ?

Looks like it is a Carter solenoid design unit?

AC Delco has an EP11 but I cannot find information about it?

Thanks,

Tim, your NAPA pump is an Airtex brand. Some say those are great, others say those are bad pumps. Hard to decide which is true. I found a lot more positive reviews than negative. Airtex is popular and is widely used. Probably an OK fuel pump. That Airtex looks to be an "impeller" type. Read on to learn about this.

Your Carter page displays the three types of electric fuel pumps. Top one, the "rotary" pump is the best type and most expensive. Those have been around for ages and prove a good pump.

Second one is an "impeller" design. Those seem to work pretty good but don't last as long as a rotary design. Mercury uses or did use an impeller design for the water pump in their outboard marine engines. I recall those have problems but this was many decades back. Primary problem was the rubber blades becoming distorted. An impeller design works on an eccentric shaft. The impeller blades fit loose on the side where gas comes in, then those blades are squished on the side where gas goes out. This squishing over and over seems to wear out those blades. Advantage is an impeller design can produce higher fuel pressure.

Last one down over at Carter, this is the one I suggest you avoid. This is the "vibrating" piston type. Those deliver fuel OK but do not "draw" fuel well from a fuel tank. This type is aimed at small four cylinder engines for the most part; low pressure, low delivery rate. I would not use one for your truck.

You can see the progression in sizes from large rotary type at top to very small with the "electronic" type at very bottom. This is a case when "size" really does matter and this size relates to reliability; larger more reliable, smaller less.

Stay away from the one at bottom, the tiny one, just bad news.

Your choice is between the large rotary type at top, and the next down impeller type. Here is the difference. The top one, rotor type, is an age old "military" grade pump, in use for many decades. The next down, impeller, was ushered into use with modern electronic fuel injection. This one is the "high" pressure type.

An old design rotor type is best for carburetors, the new impeller design is best for fuel injection.

Almost all fuel injection cars have an impeller type mounted inside the tank. Have to be reliable because of such difficulty replacing an in-tank pump. This speaks to the quality.

I installed an impeller type, the fuel injection kind second down at the Carter page, in my girl's Corvette for fuel injected flame throwers. Size is not quite as big around as a beer can and half again longer. Price tag is $350 even. I bought the best available for safety. When shooting out flames from a fuel injected flame thrower system, there can be no mistakes, this is dangerous.

Same safety principle applies to your truck. Not so dangerous but you want the best reliability possible so you don't break down on the road. An old truck, especially a nice old truck, sitting on the side of a road is an attractive target for car thieves. Classic cars and trucks are very often stripped or just outright stolen. Many end up in Japan and the Mideast. Big money market in classic vehicles; you cannot be too careful.

This is the order of reliability:

Mechanical engine block mounted
Electric rotary vane type
Electric impeller vane type

Again, forget those tiny "electronic" vibrating type.

Tim, I will again argue in favor of an old fashion mechanical type engine block mounted pump. Those are the absolute best for a carburetor type engine and virtually never break down.

If you are dead set on electric, I suggest the top of the line Carter rotary type, top of your Carter page, the big pump.

Do not try to save money on a fuel pump, do not cut corners, this is one of the most critical components of your vehicle. No fuel pump, no driving.

As said at the laundry, No Ticky, No Washy.

Be careful to not place yourself in a position of having to abandon your truck roadside, probably will not be there when you get back.

Billyray

On trips longer than 150 miles, I carry spares of many parts that are easily "field replaceable". I have had mechanical fuel pumps fail. too.