Using an electric gas pump along with the mechanical one

[R Walling]

 

If you are using an elect. pump along with the mechanical pump on the engine, will gas flow into the crank case if the diaphragm on the oem pump ruptures?

 

 I am basically using the elect. to only prime the system monetary on a 48 Chrysler, but in case of failure of the oem one, I would like to know if there would be a problem with the gas going into the crank case.

 

                                    🥵

 

Edited April 2, 2022 by Roger Walling (see edit history)

[edinmass]

It would put gas in the crankcase with or without the electric fuel pump if the diaphragm fails in SOME conditions. I would bet 95 percent of all pre war cars have an electric boot pump, or electric only pump. Just rebuild the mechanical pump every five to seven year......easy.

[60FlatTop]

Or when you touch the end of the oil dip stick and it drips off your elbow.

[kings32]

I have elec backup pumps on all my pre war cars .

[Pfeil]

18 minutes ago, 60FlatTop said:

Or when you touch the end of the oil dip stick and it drips off your elbow.

You guys!🙃

[old car fan]

The cars ran as original, why change  it.make sure insurance  is good for  when it burns. 

[West Peterson]

11 minutes ago, old car fan said:

The cars ran as original, why change  it.make sure insurance  is good for  when it burns. 

If that is truly a question, the answer is because fuel is different. Like everything, there are right ways and wrong ways of installing electric pumps. We've never had any problems, other than they need to be replaced once in a while. Not too different than having to rebuild the mechanical every once in a while.

[Bhigdog]

Electric priming saves a lot of wear and tear on the starter motor. If your regular pump is so bad as to be diluting your oil in the minute or so you run the electric it likely would not run your engine. As an aside some aircraft engines have an oil dilution system. If your aircraft is to be parked in sub zero conditions the oil is diluted with avgas when shutting down to make later cranking easier...........Bob

Edited March 31, 2022 by Bhigdog (see edit history)

[Gunsmoke]

Not quite sure how an e/pump will work in series with some mechanical pumps, and carbs, may depend on the setup (updraft/downdraft etc). The '31 Chev I had we put a temporary e/pump in line as the old fuel pump was toast. Put a switch on dash to turn pump on and off. ran fine. Once car was rebuilt I put a rebuilt original pump on engine and it worked fine so I deleted e/pump when I put new lines on car. The Chevy pump like many has inlet and outlet valves opened and closed by the diaphragm, and I'm not sure they would allow fuel by if manual pump was not working. The Chevy had an updraft carb so any excess gas getting to carb would drip onto side pans rather than into pan etc. No safer mind you. My advice: keep a well maintained original pump, mine worked great for the 10 years I owned the car, easy to service, just need to keep a couple of diaphragms available.

[Bloo]

2 hours ago, Roger Walling said:

I would like to know if there would be a problem with the gas going into the crank case.

Yes.

 

In most mechanical fuel pump designs, some of the fuel runs out on the ground when the diaphragm fails, the rest goes to the crankcase. On some designs, all the fuel goes in the crankcase.

 

An unrestricted electric fuel pump will move a lot of fuel. When one gets tired of the unreliability or noise of thumper pumps and moves up to a quality roller or vane pump, those can move even more fuel. It would truly shock you how fast an electric pump with no restriction could empty the gas tank into your crankcase. This is why most of the recommendations you see on this forum include a switch, and suggest using the pump only for priming and recovering from vapor lock. It is the best and safest way to tun an electric pump in conjunction with a mechanical pump.

 

Me? I just run original. No fuel system for a carbureted car is more reliable than a mechanical fuel pump, a metal fuel line, and a sock filter in the tank it *IF* you can make it work for you. There is a reason that setup was used for several decades. I pay extremely close attention to not having any tiny air leaks in the fuel line or fittings, and that the check valves in my fuel pump actually hold vacuum. If your fuel pump needs to be wet to prime itself, you will probably have a bad time with vapor lock. I have toured in 106F weather twice, and I have driven 2/3 of the way across the US without any fuel supply trouble. It does run a little flaky in 100F+, but it never stops running. I realize all cars are different and this may not work for everyone.

 

Edited March 31, 2022 by Bloo (see edit history)

[George Cole]

The last time I had a mechanical fuel pump fail was years ago in a 1965 cab-over GMC 2 1/2 ton truck.  The diaphragm partially ruptured, allowing gas to by-pass it and squirt out the vent hole on the top.  The stream of gas hit the coil, shorted it out, and stalled the truck.  Amazingly, no fire.  George

 

[Mark Gregush]

Bhigdog I think nail it. Most of these cars can sit for weeks or months. Electric pump used as a primer, would in my OP be a good idea. 

[alsancle]

The electric pump serves three purposes:

 

1.  Priming.

2.  Overcoming vapor lock

3.  redundancy for mechanical failure.

 

I've had at least 3 mechanical pumps fail on me.    The electric pump needs to be switched and the pressure turned down.  More than a few pounds will blow past most needle valves.   I've seen setups with pressure valves and returns.

 

Also,  they need to have zero restriction for pull through by the mechanical pump.

Edited March 31, 2022 by alsancle (see edit history)

[trimacar]

The electric fuel pump serves a fourth purpose, if there’s no cutoff switch it feeds the fire.  Even with a cutoff switch, things can go awry.  I almost lost two excellent cars to electric fuel pumps.

 

Mechanical fuel pumps, and vacuum tanks, worked great when cars were new.  Rebuild them correctly and one can’t go wrong.

 

Yes, I know many will say “yes, but electric pumps are new and better”.

 

However, no period car would have been sold had the original system not worked well and correctly.

[Ken_P]

44 minutes ago, trimacar said:

The electric fuel pump serves a fourth purpose, if there’s no cutoff switch it feeds the fire.  Even with a cutoff switch, things can go awry.  I almost lost two excellent cars to electric fuel pumps.

 

Mechanical fuel pumps, and vacuum tanks, worked great when cars were new.  Rebuild them correctly and one can’t go wrong.

 

Yes, I know many will say “yes, but electric pumps are new and better”.

 

However, no period car would have been sold had the original system not worked well and correctly.

While I appreciate your perspective, this is a bit of a straw man. Fuel has fundamentally changed since these cars were new. With modern fuels having a much lower boiling point, an electric pump can correct problems that didn’t exist when these cars were new. The many fuel atomizing systems  of the past (heat risers, spark plugs in the intake, etc) highlight that 70-100 plus years ago, manufacturers had the opposite problem, because of the high boiling point and difficulty atomizing the fuel of the day.

[Bloo]

That's also a bit of a strawman, but not entirely wrong.

 

Carburetor heat is necessary, and there has never been any even remotely modern carbureted or throttle body injected car sold in the USA without intake manifold heat that I am aware of. Maybe some NASCAR homologation specials. My 91 Geo Metro has a hotspot under the TBI. I always hear heat risers are for "cold climates". No. The reason the hotspot exists is because without a hotspot fuel falls out of the air at the first bend, runs to the end of the manifold, and washes down the rings, causes excessive wear, and winds up in the crankcase oil. The mixture also has to be richer too because of the horrible fuel distribution. Cars made in the 20s when gas was full of kerosene-like fractions because the refineries couldn't keep up may need far less heat riser heat than they originally did, so that is sort of an exception. It doesn't negate the need for heat altogether. The car I just drove through several states (1936 Pontiac) has a working heat riser and runs much better than when it didn't. I use 10% Ethanol fuel.

 

I am constantly hearing that the fuel is different and more volatile, but unless we are talking about cars made before the mid 30s, I think it's usually just an excuse to not look for a problem in a broken car. I know in the 80s fuel was blended to a specific reid vapor pressure for the climate it would be sold in, and the target changed from summer to winter. In those days Ethanol, Methanol, and MTBE were used as octane boosters, in a total blend of 10% or less. Methanol and MTBE boil at lower temperatures than Ethanol. Until I see some actual evidence that the oil companies are blending fuel to a higher reid vapor pressure today than they were in the 80s when carburetors and mechanical fuel pumps still ruled, I am not going to believe it.

 

Electric setups can solve problems... and create new ones, like the one @trimacar brought up. What happens when the fuel line is ruptured in an accident? Any rubber hose in the system should be replaced with SAE 30r9 fuel injection hose because it is ethanol compatible, not prone to pinholes, and most of all because it is difficult to tear. I'll repeat that it will shock you how much fuel an electric pump moves when fully uncorked. I have taken several approaches to mitigating this in the past. One thing I did was copy a Toyota idea where the pump would run when the starter runs, filling the bowl with fuel. Then, the pump would not come on again until the oil pressure came up. If the engine is killed for any reason, the fuel pump goes off. Another approach I have used is an inertia switch, as used by Ford, Alfa Romeo, and Jaguar. They shut the fuel pump off on impact. The best switches are the ones that Ford used from the mid to late 80s. The Jaguar and Alfa Romeo switches are less reliable.

 

Then there is fuel pressure. A lot of old carbs that had mechanical pumps run 2-3psi, and very few electric pumps support that. Most are 4-5psi or 7-8psi. That calls for a regulator, and good ones are expensive. Carbs that ran gravity originally will need a different needle and seat, as @carbking has posted about many times.

 

The idea of having a switch and only using the pump when needed makes a whole lot of problems go out the window. The only caveat is that the electric pump has to not restrict flow when off, so thumpers are fine, but if you want a real vane pump that wont ever fail, you probably need some check valves too.

 

[trimacar]

2 hours ago, Ken_P said:

While I appreciate your perspective, this is a bit of a straw man. Fuel has fundamentally changed since these cars were new. With modern fuels having a much lower boiling point, an electric pump can correct problems that didn’t exist when these cars were new. The many fuel atomizing systems  of the past (heat risers, spark plugs in the intake, etc) highlight that 70-100 plus years ago, manufacturers had the opposite problem, because of the high boiling point and difficulty atomizing the fuel of the day.

A correctly rebuilt original mechanical fuel pump, and a carburetor correctly set up for modern fuels (slight jet size modification), compensates for any modern fuel issues.  My opinion and experience, after owning 200 plus collector cars (most of which were pre-WWII) and driving many more, is that electric fuel pumps cause more problems than they solve.  But, that’s just my opinion.

[Ken_P]

9 hours ago, trimacar said:

A correctly rebuilt original mechanical fuel pump, and a carburetor correctly set up for modern fuels (slight jet size modification), compensates for any modern fuel issues.  My opinion and experience, after owning 200 plus collector cars (most of which were pre-WWII) and driving many more, is that electric fuel pumps cause more problems than they solve.  But, that’s just my opinion.

Fair enough. And I should note that my  car (‘37 Packard 120) only has a mechanical fuel pump, and I haven’t had any issues.

 

When you re-jet for modern fuel, do you go slightly smaller or slightly larger? Main jet, idle circuit, or both? (I assume main) What’s the theory behind it? Thanks! 

 

Also, sorry for the slight thread hijack.

Edited April 1, 2022 by Ken_P (see edit history)

[Bloo]

In theory larger, because alcohol needs to be mixed richer than gasoline to get a balanced mixture, so with a little alcohol in there....

 

In practice there are real life complications. The specific gravity of the fuel is slightly different. Enough to change the float level enough to alter the mixture? I don't know. The specific gravity of Ethanol is higher than gasoline, so that should shut the float of slightly sooner, leaning things out even more (but remember it's only 10% of the fuel). My best guess it it doesn't matter. Some cars were jetted too rich in the first place, especially before the late 30s. My Pontiac has a "taxicab" metering rod in it, 2 steps leaner than standard, and I think I could get away with a third step leaner if Carter made the parts (they didn't). That is the opposite of what you would probably expect. I'm at 800 feet above sea level, and the mixture richens automatically as you go up in altitude due to less dense air.

 

I wouldn't be in a hurry to change anything unless the mixture was proven to be wrong on a gas analyzer.

 

[edinmass]

Every pre war car I own and maintain has an electric fuel pump on it. I only run all my Pierce Arrows on electric only, and use the mechanical as a bypass. I don’t count my Model T as a car..........

 

Every car should be tested on a five gas machine and a chassis dyno to properly tune it. And EVERY pre war carburetor today requires modifications to get them to run correctly..........and not just a main jet change.

[F&J]

All the guys that hate electric booster pumps, how are you starting your 6v cars when this modern gas evaporates the carb bone dry in such a short time?

 

are you just cranking the living sh-t out of the poor starter?

 

 

BTW, one local guy's son put an outboard boat motor hand squeeze bulb near the tank on his dad's 32 Plymouth roadster. It works....but...He has to reach under the back of the car to start the damn car. 

 

non ethanol is not sold here.

 

.

 

 

 

 

[Ken_P]

6 hours ago, edinmass said:

Every car should be tested on a five gas machine and a chassis dyno to properly tune it. And EVERY pre war carburetor today requires modifications to get them to run correctly..........and not just a main jet change.

Well, that should be easy to find 😂 🤦‍♂️.

 

Seriously though, thanks for the input. 

[60FlatTop]

I have been under the impression that modern fuels are less volatile than in the past. I can leave a glass filter bowl on the bench for a couple of weeks and nor notice evaporation.

 

I do know a lot of older carburetors have plugs that leak when they age. They are in the bottom of the fuel bowl, at the end of passages, and hidden by the base flange. A leaky one can make it appear the fuel evaporated and that is the stuff folklore is made of.

 

A lot of people are out there rebuilding fuel pumps, carbs, and such. But to make things work you have to service it as a system. Without addressing all the interacting parts one might fool themselves into thinking they made it work. It is all in the details and the willingness to probe deeply into the system. If you have a rubber hose connection between the fuel tank and gas line how old is it? When was it checked last? They can get old and leak air under a vacuum but not leak liquid when idle. I worked on a ;32 Hudson once that had a pressure reducer between the vacuum tank and the carb. It was set on the dial at 3#. I mentioned an inertia switch to a friend who had a electric pump. He didn't need it. In an accident he would shut it off.

I have recommissioned many cars that sat for a long time. I disconnect the carb fuel inlet and pull a vacuum on the line with a MyTeeVac breeder. I pull three containers of fuel to look at the condition and get everything wet in the system. That can keep an old dry diaphragm from rupturing, at least help it flex. And I have fresh fuel right at the carb to save on starter brushes.

Most of the things I have had to fix in my various jobs have worked fine once I put everything back to design, removed the added improvements, and repaired them systemically. Not much chance of charging things at this point.

[usnavystgc]

Ok, here's my $.02.  I recently felt like I had to install an electric fuel pump on my 56 Super.  My pump is a pull thru design with a cut off switch on the lower dash (5-9 psi rating).  I live @ 3K ft in a hot climate.  At this elevation the boiling point of fuel becomes lower and I have experienced vapor lock on several occasions (at the worst times too).  Since the installation of my electric pump I can easily overcome any vapor lock situation and can now drive the car confidently in just about any condition.  Without it, I'm seriously afraid to drive the car.

 

I am a 100% advocate of stock systems, it honestly killed me to have to install the electric pump but, I also want to enjoy driving my car without worrying about vapor lock or spending 45 minutes waiting for the car to cool down so it will start again (which I've had to do).  I only use the pump when I'm in fear of a vapor lock situation.  I honestly don't see another solution.  Modern cars use high pressure electric fuel pumps that significantly increase the boiling point of fuel.  

 

Is this sound logic?  The reason i ask is because I see a lot of people commenting that they use only a mechanical pump and have no problems.  That has not been my experience.

[Ben Bruce aka First Born]

I think you are wise, Phil.  

 As most who know me know, I have fuel injection on my 1950.  No way I would EVER go back to a carburetor. Just no need in fighting today's gas. I would do the same if I had yours. It can be done on yours and no one would know if you did not tell.   Who among us would stick with an old tube TV?  Or an icebox instead of a refrigerator?  Analogy not perfect, I know.

 

  I will put my chain mail on now.

 

  Ben

 

  

[F&J]

21 minutes ago, usnavystgc said:

I also want to enjoy driving my car without worrying about vapor lock or spending 45 minutes waiting for the car to cool down so it will start again (which I've had to do). 

 

Is this sound logic? 

You are using perfect logic.  Nice to hear that you drive your car a lot, too. 

 

 

Some are making blanket statements about not needing a booster pump.  AACA members each own a different decade of cars;  underhood components that differ greatly, where the carb, pump & lines are, in relation to super hot components.   That leads to drastic differences in heat-sink evaporation as well as differences in vapor lock frequency.  We also live in vastly different climates

 

You also can't go by a test of cold gas in a cold jar inside the shop. Put that gas in a hot carb bowl and set it on a boiling hot engine after a long drive, and low and behold...it disappears.  Some fuel bowls are very low volume, and will evaporate to completely empty quicker than huge ones.

 

Most people in my cooler climate with electric booster pumps, use it not for vapor lock, but for carbs that begin to evaporate quickly on hot shutdowns, (they actually drive their car a lot).  They want to avoid the abuse on the vintage starter motor while trying to refill the carb after the car sits a few days. 

 

For a couple of years now, the mix rate of alcohol is increasing, and I see the day when some brands of vintage car designs in hotter climates like Ben has, will be forced to go with EFI. 

 

26 minutes ago, Ben Bruce aka First Born said:

I will put my chain mail on now.

Ben, just how... ummm...elderly are you...Medieval?? LOL ..   I wonder how many people know what "chain mail" is.  I only knew as I've seen videos of people digging pieces of it up in European fields. 

[Matt Harwood]

As someone who drives hundreds of different cars and has to start all different kinds of cars that have been sitting for days, weeks, months, I will way that without exception, I am greatly relieved when a car has an electric fuel pump. Without one, it's usually a race between the mechanical fuel pump and the starter to get the carburetor filled before the battery is dead. I am usually able to tell when a car won't be starting quickly or easily and give it a tablespoon of fuel down the carburetor to get it to catch, but that's not only inconvenient, it's dangerous. I greatly prefer letting the fuel pump run for 10 seconds then cranking it. 7 times out of 10, it fires quickly and easily.

 

While I agree that in theory a healthy mechanical pump and properly tuned engine should be easy to start, they are usually not. There are several reasons. Today's fuel does indeed evaporate more quickly and after about a week, the carburetor is dry. It takes a mechanical pump quite a long time to refill the bowl at cranking speeds. In addition, I have learned that very few cars are properly set up and tuned. I guarantee there are guys reading this right now with soggy fuel pump diaphragms and poorly tuned carburetors but think their car is fine. An electric fuel pump can overcome those shortcomings and get the car running so they can enjoy it--there's no crime in that. Sadly, I would guess that fewer than 20% of all old cars are "properly" tuned and few start easily after a period of inactivity. I guarantee I haven't somehow managed to find the only cars with issues. So yes, in that way the electric fuel pump can be a band-aid, but most old cars suffer the same symptoms even if the causes are different.

 

And that's ignoring the very real benefit of a fuel pump on a hot day. My 1941 Buick is virtually immune to vapor lock due to my exhaust headers replacing the manifolds, but occasionally on hot days after a long high-speed run on the highway, I will come to the bottom of an exit ramp. At that red light, the engine drops to 400 RPM, the mechanical pump virtually stops moving fuel, the fan barely moves any air, coolant flow slows, and it just soaks in the heat. Sometimes it will vapor-lock and stumble when I try to accelerate away from the light. However, switching on the electric pump as I am coasting to a stop ELIMINATES the problem. Again, it's today's fuel that's the issue, something they didn't really contend with when the car was new. It could be considered a band-aid to some, but I prefer this solution to clothes pins or foil or insulation wrapped around the fuel lines or kerosene/diesel in the gas to try to prevent it.

 

If you can just flip a switch to make your old car more manageable in today's world, why wouldn't you do it?

[usnavystgc]

Ok, its good to know I didn't waste a whole Saturday doing something that didn't need to be done.

[Ben Bruce aka First Born]

1 hour ago, F&J said:

 

😁😁

 

Not quiet Medieval, Frank, just almost.

 

  Ben

[Bhigdog]

1 hour ago, Matt Harwood said:

If you can just flip a switch to make your old car more manageable in today's world, why wouldn't you do it?

Indeed!.............Bob

[hidden_hunter]

9 hours ago, F&J said:

 

All the guys that hate electric booster pumps, how are you starting your 6v cars when this modern gas evaporates the carb bone dry in such a short time?

 

My car from the factory has a hand pump to prime it and then the air compressor forces air into the petrol tank to circulate the fuel. Takes about 5 pumps to get enough fuel into the carb to start

 

 We don’t really use ethanol fuel here

 

If you have everything in the correct position it will fire almost immediately after sitting for a month

Edited April 1, 2022 by hidden_hunter (see edit history)

[F&J]

1 hour ago, hidden_hunter said:

My car from the factory has a hand pump to prime it and then the air compressor forces air into the petrol tank to circulate the fuel.

This pic will look familiar to you?  I think around 1920 Cadillac?   It's in my 32 Ford that I use year round as primary car.  I used the small former air pressure line to be a vent line under the car furthest to the back.

 

I like having the mechanical gauge for when I put gas in, as I don't ever fill it to 20 Gallons.  Also made a electric sender spot for my dash gauge. 

 

These were sometimes used right after WW2 at Bonneville salt races, as many cars used pressurized fuel systems.

[hidden_hunter]

21 minutes ago, F&J said:

This pic will look familiar to you?  I think around 1920 Cadillac?   It's in my 32 Ford that I use year round as primary car.  I used the small former air pressure line to be a vent line under the car furthest to the back.

I’m guessing a type 57 or type 59

[Marty Roth]

On 3/31/2022 at 3:39 PM, kings32 said:

I have elec backup pumps on all my pre war cars .

I do also, and also on my post-WWII cars 
(auxiliary from the oldest through the 1965, and standard on all later ones) 

either to prime a system for easy starting,

or to overcome Vapor Lock

[SC38dls]

An easy fix for fuel evaporation in the fuel bowl is to take a half grapefruit and shove it on the bowl. Works as a great insulator and the only problem is finding the grapefruit!  We found this worked easily in FL during spring break back in college when we spent all our $ on beer and girls not on car repairs. The grapefruit was everywhere for the picking! 
dave s 

Edited April 2, 2022 by SC38dls (see edit history)

[Marty Roth]

11 hours ago, SC38dls said:

An easy fix for fuel evaporation in the fuel bowl is to take a half grapefruit and shove it on the bowl. Works as a great insulator and the only problem is finding the grapefruit!  We found this worked easily in FL during spring break back in college when we spent all our $ on beer and girls not on car repairs. The grapefruit was everywhere for the picking! 
dave s 

The grapefruits were everywhere for the picking,

and so were the girls,

at least in the early - mid 1960s-

and I prefer not to imagine what some of those same "girls" look like today,

but if I turn sideways, hold my breath, and squint really hard,

I'm just celebrating the 60th Anniversary of that Ft. Lauderdale Spring Break !