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  • Fuel System: Vapor lock and heat soak

    I’m finally ready to address heat soak and vapor lock on my ’50 Commander and I have some questions….

    First I’d like to add a phenolic insulator spacer where the carb mounts to the inlet manifold but the exploded view diagram in the chassis parts catalog does not show the studs separate from the inlet manifold. Is this right, are the studs part of the inlet manifold and not replaceable independently? If so I'd be hard pressed to squeeze in a ¼” spacer, especially if gaskets are required on both sides of the spacer. Are they?

    Next I’d like to add an electric fuel pump which means fuel line inlet and outlet ports on my mechanical fuel pump will become open. On the Commander the fuel pump also provides vacuum for the windshield wipers. My first inclination was to plug the unused fuel ports but it occurs to me that could prevent the diaphragm from working for the wiper motor. Should the unused fuel line ports on the mechanical fuel pump get plugs or not?

    I probably won’t go with an in-tank electric fuel pump because I’d have to bore a new hole in the tank. And even though in-tank fuel pumps come with a foam gasket that supposedly compensates for ribs on the skin of the tank if I ever wanted to service it I’d need to either cut a new access panel in the trunk floor or drop the whole tank. Plus, an in-tank fuel pump cost several hundred more dollars than an inline one. (I could still be swayed though.)

    That leaves the option of an inline electric fuel pump, fuel filter (since the old one was part of the mechanical pump), vapor separator, and vapor return line with check valve. I’d probably bore a hole on top of the existing sending unit and add a fitting sealed with JB Weld for the vapor return line. What pressure fuel pump should I get? And how does the tank deal with pressure introduced through a vapor return line? Would that require adding a relief mechanism? If so, could a vented gas cap take care of it?
    Last edited by Tipjar; 06-23-2022, 08:00 AM.

  • #2
    I'm sure you'll need 2 gaskets. I leave mechanical pump alone and install the electric pump back near the gas tank. I wire it with a fuse to the acc circuit - easy to access by using a 1 to 2 wire union on the acc lead on the heater switch or anything handy. Use a mechanical pump; a vane pump is not self- priming. This will enable you to switch to acc and pump gas up to the carb without grinding away on the starter and running down the battery. Once the car starts, you can switch the electric pump off and use it as a back-up in case of mechanical pump failure. I've never installed a return line as pumps are -- or should be--pressure regulated. They'll switch themselves off at about 4 psi. Can't remember! Is a 50 a 6 or an 8? There is a heat shield that often gets lost and is helpful in preventing vapor lock in 6's. Be sure filter is between pump and gas tank. Hope that helps. Be sure you're not too lean and see if a couple degrees more advance helps any. It is not the car that is at fault --it is the terrible gas we have now. I'm sure it is worse in CA.

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    • #3
      The 1950 Commander is the last year of the Commander six in a car.

      There are two heat shields on a 1950 Commander.

      One is under the carburetor base and shields the float bowl. The other is attached to the side valve cover and shields the fuel pump.
      RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.


      10G-C1 - 51 Champion starlight coupe
      4H-K5 - 53 Commander starliner hardtop
      5H-D5 - 54 Commander Conestoga wagon

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      • #4
        I would just run a return fuel line and see how well it works. It cured my vapor lock problems. I ran it from a fuel filter with a return port to a fitting on the metal portion of the filler tube.

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        • #5
          Originally posted by Jeffry Cassel View Post
          Is a 50 a 6 or an 8?
          1950 Commander was still a 6-cylinder, 245 cu in, 4.0L.

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          • #6
            Yeah, I knew 51 was the first year for V8. Lots of stuff in the old noggin but, like my shed, gettin' to it is some times problematic!! That heat sheild helped mine but it is queen of the garage.

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            • #7
              Just understand that a "Return Line" on an Older Car, is NOT like you are thinking like on a New Car. It is NOT VAPOR! It is a restricted amount of Fuel Return to keep the Fuel Cool and flowing to prevent Vapor Lock, an entirely Different System.

              And, ONLY 1962 to 1966 Larks, Lark Types and Avantis have a Tank Vent Tube so use a Sealed Cap, so ALL others MUST have a Vented Cap.

              Usually a High Volume Fuel Pump is used, to have enough volume to bleed off some and not run short at high RPM.
              But with a Low RPM Engine like a Commander Six, that should not be a problem.
              Last edited by StudeRich; 06-23-2022, 01:20 PM.
              StudeRich
              Second Generation Stude Driver,
              Proud '54 Starliner Owner

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              • #8
                Originally posted by StudeRich View Post
                Just understand that a "Return Line" on an Older Car, is NOT like you are thinking like on a New Car. It is NOT VAPOR! It is a restricted amount of Fuel Return to keep the Fuel Cool and flowing to prevent Vapor Lock, an entirely Different System.

                And, ONLY 1962 to 1966 Larks, Lark Types and Avantis have a Tank Vent Tube so use a Sealed Cap, so ALL others MUST have a Vented Cap.

                Usually a High Volume Fuel Pump is used, to have enough volume to bleed off some and not run short at high RPM.
                But with a Low RPM Engine like a Commander Six, that should not be a problem.
                Good information. Thank you StudeRich.

                Comment


                • #9
                  Originally posted by RadioRoy View Post
                  The 1950 Commander is the last year of the Commander six in a car.

                  There are two heat shields on a 1950 Commander.

                  One is under the carburetor base and shields the float bowl. The other is attached to the side valve cover and shields the fuel pump.
                  Well, Radio Roy, once again you’ve provided a vital clue….

                  This is the first I’ve heard of heat shields for the carb and pump. I forgot to mention I was planning on making a shield to fit under the insulator spacer. News of their existence helps explain what I consider to be a suspicious frequency with which the car has gone into vapor lock/heat soak while the cooling system has remained within the safe zone.

                  When I got the car it had the wrong fuel pump (a single diaphragm off a ’48) which I corrected, and just yesterday I figured out according to the parts book it’s also got the wrong carburetor (a Carter WA-1 rather than a Carter WE-6275A). Apparently past tinkerers lost the shields.

                  I don’t see the shields in illustrations for the engine or fuel system, but looking through descriptions in the fuel system section I see for the 17A a “fuel pump shield” part number 187748 and “shield, carburetor” part number 187670. Also, a search brings up a helpful pic of the carb shield in a past thread which you happened to comment in: https://forum.studebakerdriversclub....0-heat-shields

                  This has got me wondering if heat shields, an insulator spacer, and vapor separator with return line would be adequate but I’ll continue exploring all avenues. I'm torn between wanting to be sparing with modifications to preserve as much authenticity as possible, and wanting to do whatever it takes to solve the problem without having to return to it. I’ll start calling around for NOS shields tomorrow. I happen to have a laser cutter and could cut my own. If I were to try the link above has a pic of the shield for the carb but I’d still need a pic of the shield for the fuel pump.

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                  • #10
                    The other correct carburetor is a BXOV-26, if memory serves.

                    There is precious little room between the oil bath air cleaner and the underside of the hood. I found that out when installing an injector plate for an upper cylinder lubricator. Installing a spacer under the carburetor should be a last resort because of the lack of space. Maybe you could find a dry air cleaner, because they might be shorter, but only if the heat shields do not do the job.

                    An electric fuel pump by the gas tank is very helpful in eliminating vapor lock.
                    RadioRoy, specializing in AM/FM conversions with auxiliary inputs for iPod/satellite/CD player. In the old car radio business since 1985.


                    10G-C1 - 51 Champion starlight coupe
                    4H-K5 - 53 Commander starliner hardtop
                    5H-D5 - 54 Commander Conestoga wagon

                    Comment


                    • #11
                      I think that "Vapor Lock" is the most misunderstood fuel management issue, there is probably at least a dozen examples of "Vapor Lock" and as many cures for the problem. Fuel can boil in the carburetor for various reasons and when fuel boils in the carburetor the fuel will boil over into the throat of the carburetor and over fuel the engine causing it to fail. This condition is very common and is often labeled as "Vapor Lock". The engine will cool down after a short time and will restart with no issues. Boiling fuel in the carburetor can be a result of engine overheating caused by inadequate cooling, eg contaminated block and/or radiator or insufficient coolant in the system. Also in many cases the heat riser is malfunctioning or is installed upside down causing excessive heat to develop at the base of the carburetor, this condition will surly boil the fuel in the carburetor and this is not a "Vapor Lock". There are many owners that participate in parades in 100* temperatures and do not experience any fuel management issues. Even with 100* air temperatures the engine will operate at 160*- 180* and may climb a little higher at lower speeds but should not boil the fuel in the carburetor. I have a 259 with a clean block and radiator with a 160* thermostat and it can idle for an hour at 100* air and the engine temperature on occasion will elevate to 170* never any higher.

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                      • #12
                        Originally posted by altair View Post
                        I have a 259 with a clean block and radiator with a 160* thermostat and it can idle for an hour at 100* air and the engine temperature on occasion will elevate to 170* never any higher.
                        Not exactly a good comparison David. I have similar results with my 289. But I have a 180 thermostat and electric fan that comes on at 195. It can sit and idle in my garage all day in 100 degree temps and never go over 200 degrees. But, that's not the same as rolling under load. Under load, with the same conditions, my coolant temp will run around 203-205 at highway speed when air flow is high, but after pulling into town where air flow is not 60+ mph the temp will go up 10 degrees while under load. Once parked the temp will drop after several minutes and it can idle the rest of the day at 200 or less.

                        Part of the increase in low speed under load temp is due to trapped under hood heat. The easiest/ fastest way to eliminate a minor to moderate excessive coolant temp situation , at least in the short term, is to simply remove the hood. Most probably want their hood in place though.

                        On my Hawk I installed a system to vent under hood heat. When activated under hood temp drops considerably, and coolant temp follows to a lesser degree. Prior to installing this system; I was able eliminate both vapor lock and boil over issues by installing an electric pump near the fuel tank, installing a thick phenloic spacer under the carb, re-routing the fuel line to keep as much of it out of the engine compartment as possible and insulating that which is inside the compartment.

                        FYI, My target coolant/running temp is 195-200. I run aircraft quality digital temp gauges, both oil and water, and have underhood sensors to read under hood temp, and one to read ambient temp. BTW, my oil temp runs at 185-190.

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                        • #13
                          I installed an electric fuel pump on a switch in both my '55 President and '61 Champ truck to cure the occasional vapor lock issue. The moment the engine begins to sputter and buck on a hot day I switch on the electric pump and it smooths right out. If it is a really hot day like those we had last summer, I turn the pump on before I even start the engine and just leave it on. Works every time.
                          Ed Sallia
                          Dundee, OR

                          Sol Lucet Omnibus

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                          • #14
                            Originally posted by RadioRoy View Post
                            There is precious little room between the oil bath air cleaner and the underside of the hood.
                            I noticed. And did some space tests and think I came up with 3/4" maximum clearance to play with, so a 1/4" spacer with two gaskets should be okay but I think it would be too close for comfort with a 1/2" spacer. Either way I'd need longer studs on the inlet manifold, which if they're not removable could be some extra work drilling and tapping. Things to think about...I located the fuel pump heat shield on a vendor's website today. They weren't answering their phone, waiting to hear back by email.

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                            • #15
                              Originally posted by bensherb View Post
                              On my Hawk I installed a system to vent under hood heat. When activated under hood temp drops considerably, and coolant temp follows to a lesser degree.
                              This is another idea I was considering. How did you do it? Did you add another fan directed at the exhaust manifold? Create louvres on the inside fender wall?

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