Author Topic: 1956 Coupe Deville Fuel Pump  (Read 222 times)

Offline John Gaynor

  • Posts: 5
  • Name: John Gaynor
1956 Coupe Deville Fuel Pump
« on: November 06, 2017, 11:17:53 AM »
I just change the fuel line, fuel tank, and fuel pump in my 1956 Coupe DeVille.  I noticed that the fuel filter bowl is not filling up. Should the fuel filter bowl loose all air or is it normal to see air in the fuel filter bowl. I am trying to determine if the fuel pump is working correctly.

Offline carguyblack

  • Posts: 563
  • Name: Chuck Dykstra
Re: 1956 Coupe Deville Fuel Pump
« Reply #1 on: November 06, 2017, 01:03:58 PM »
My sight glass is installed glass-side down and it is never full. It shows maybe half at all times but when running can see movement through it. Hope this helps.
Chuck
Chuck Dykstra

Offline John Gaynor

  • Posts: 5
  • Name: John Gaynor
Re: 1956 Coupe Deville Fuel Pump
« Reply #2 on: November 06, 2017, 01:54:53 PM »
Okay, the car seems to be running okay, just want to confirm that air in the glass bowl (1/2 to empty) is normal when the car is running. I probably should take it for a longer run on the highway to insure I am getting enough fuel to the carburetor.

Offline lexi

  • Posts: 196
    • CLC Member
      CLC Member #28634
  • Name: C.R. Foley
Re: 1956 Coupe Deville Fuel Pump
« Reply #3 on: November 06, 2017, 03:19:23 PM »
With my '56 it seems to depend on both ambient temperature and also engine running temperature. First start up on fast idle the bowl is full of gas. I may or may not see an air bubble in there, at the top, (glass bowl mounted with glass side up as per OEM). If your glass fuel filter is upside down, it will be closer to the engine heat. Not good. Once I go around the block a couple of times it may only be half full, again depending on heat in the engine bay area which is also tied into the ambient temperature to a point. If it is summer, it is always 'empty' when I return home from a cruise, though you can see gas getting through much like coffee percolating in an old fashioned coffee brewing pot; you know...with the coffee 'jumping' around in that little sight glass, (glass is not full but you see the fluid passing through in spurts).

With my vehicle it takes about 20 minutes of running for this empty, or near empty fuel bowl situation to occur. The hotter the engine the shorter the time it takes. The Administrator for the Mid-Century Cadillac CLC Forum did a series of electronic temperature readings on his '56 Eldo and as I recall, 20 minutes was about it before early signs of fuel percolation were noted, when just parked idling in his driveway. If your cooling system is not 100%, or are using fuel with a lower boiling point, these factors in theory would also not help. If you have the standard 4 bladed radiator fan then expect the system to run hotter, thus aggravating any fuel percolation issues, (especially if you are also running an AC compressor). You can test your fuel pump with a vacuum gauge and also run some volume tests to determine whether it is operating properly. The shop manual also has specs for the push rod length (which drives the mechanical pump), should you determine that additional investigation is necessary. Even so, the above issues are a fact of life for these cars, especially the '56's as they ran 'hot' even when new. Based on your comments your car may indeed be operating "normal' with respect to this matter. Clay/Lexi
« Last Edit: November 06, 2017, 03:37:21 PM by lexi »

Offline John Gaynor

  • Posts: 5
  • Name: John Gaynor
Re: 1956 Coupe Deville Fuel Pump
« Reply #4 on: November 06, 2017, 06:10:50 PM »
Thank you for the input, I am going to take the car for a longer run to see if I have any issues.

Offline lexi

  • Posts: 196
    • CLC Member
      CLC Member #28634
  • Name: C.R. Foley
Re: 1956 Coupe Deville Fuel Pump
« Reply #5 on: November 06, 2017, 10:09:07 PM »
John you are welcome. Let us know how things are at highway speeds. Clay/Lexi

Offline carguyblack

  • Posts: 563
  • Name: Chuck Dykstra
Re: 1956 Coupe Deville Fuel Pump
« Reply #6 on: November 07, 2017, 05:55:36 AM »
There has been a lot of debate about the proper way to mount the glass bowl fuel filter over the years. I don't have my car home right now to look, but it seems to me that my air filter would have been in the way for me to have swung the glass bowl in the up position. I've had 3 of these cars (in Michigan- cooler climate usually, I know) with the bowl down and never experienced a fuel boil nor a vapor lock. The engine area gets piping hot but I never thought the 3 inch difference in positioning the fuel bowl made a difference in my experience. I just personally liked the way it looked hanging down and seemed to make more sense to me that sediment then would fall to the bottom of the bowl.
Chuck Dykstra

Offline lexi

  • Posts: 196
    • CLC Member
      CLC Member #28634
  • Name: C.R. Foley
Re: 1956 Coupe Deville Fuel Pump
« Reply #7 on: November 07, 2017, 10:46:36 AM »
I am always amazed at how some cars of the same model year were plagued with vapor lock while others were not. Chuck I am glad to hear that you have dodged this bullet over the years. There are obviously a set of variables at work here that all are best to avoid triggering. Mounting the glass bowl upright may prove to be a "little big thing" for some of these cars. I believe that it is also factory correct, from a purists perspective. I never had an issue with it making contact with the air cleaner though. Having the glass bowl upside down does seem to make more sense as well to me, but leave mine as OEM installed.

In 1976 I bought my first vintage Cadillac, a 1956 Coup de Ville and it vapor locked routinely over the 7 years I owned it. It was a nightmare. Could never get rid of it. My current '56 has so far avoided full blown vapor lock. My current ride does have a 6 bladed dealer installed fan which probably has helped. Everything else remains the same, even where I live, (though fuel blends have changed and not for the better). To this day I don't know why my CDV was such a problem. Reading the old bulletins it is clear GM knew there was an issue with these cars running hot so I do my best to avoid "tempting fate" so to speak, and try to keep the fuel system as cool as possible.

At any rate, it seems that John thus far probably does not have a problem with his fuel delivery.  John, attached is the Mid Century Cadillac link that I discussed. Looks like the video no longer plays but there are plenty of photos and text which discusses full and empty fuel bowls on an idling 1956 Cadillac engine. Clay/Lexi

http://midcenturycadillacs.com/index.php?topic=516.msg3219#msg3219
« Last Edit: November 07, 2017, 10:54:01 AM by lexi »

Offline gary griffin

  • Posts: 2058
  • garygriffin@Q.com
    • CLC Member
      CLC Member #26430
  • Name: Gary Griffin
Re: 1956 Coupe Deville Fuel Pump
« Reply #8 on: November 07, 2017, 11:24:38 AM »
John,  Your bowl is always full, if not of gasoline unless you have a leak it is full of gas (Vaporized gasoline).  Look at the many "vapor lock" posts.  The state of a liquid to gas depends on pressure and temperature, The stability depends on the time it was refined as mix recipe changes and formula is based on 6 weeks storage ind is directly affected by vicinity of the market it is designed for.. In the winter it has a lower "Flash point" which is the point it flashes form liquid to gaseous state. Fill up for Christmas drive then try to drive on a hot day in July and vapor lock occurs. We can easily have no liquid in the bowl and the car runs as it is compressed back to liquid by pump and vaporized again by the carburetor. Fill up in July and you may have a hard time starting for the Christmas drive.  Our fuel pumps suck the gas from the tank thereby lowering the flash point. If it is running well especially on hot days you are O K if not follow the ideas on in the vapor lock posts.
Gary Griffin

1940 LaSalle 5029 4 door convertible sedan
1942 Cadillac 6719 restoration almost complete?
1942 Cadillac 6719 (parts car) (Gone)
1957 Cadillac 60-special (Needs a little TLC)

Offline J. Gomez

  • Posts: 1444
    • CLC Member
      CLC Member #23082
  • Name: J. Gomez
Re: 1956 Coupe Deville Fuel Pump
« Reply #9 on: November 08, 2017, 08:32:05 AM »
Iím not a hydraulic engineer so my comments may well be on the wild side or just cuckoo.  ;D

With the ďopenĒ fuel setup on these vehicles there will be both fuel and air being pumped, so the fuel bowl would have both.

From what I recall back on my school time during the ice-age  :D ,air is difficult to compress, and with the fuel pump having a 4-6psi there is no way the bowl will be 100% full.

Iíve used both the mechanical and electric fuel pumps and neither can get the bowl completely full, max Iíve notice was about Ĺ full.

The video posted by Lou at the Mid-Century site (link under Clayís post) did show the fuel delivery was irregular at idle as the engine ambient temp increased. So obviously there is an impact on fuel delivery from multiple factors when temp increases.

Iíve also recall seeing a couple of YouTube videos from John Washburn showing a similar symptoms on a 1949 -1950 Cadillac. Maybe he can chime in if he is around.
 
Chuck,

There was a similar discussion related to the fuel bowl position you can check it here -> http://forums.cadillaclasalleclub.org/index.php?topic=129835.msg336618#msg336618

HTH
J. Gomez
CLC #23082

Time is irrelevant when you work on your classic car, eventually you will enjoy it..!

Offline lexi

  • Posts: 196
    • CLC Member
      CLC Member #28634
  • Name: C.R. Foley
Re: 1956 Coupe Deville Fuel Pump
« Reply #10 on: November 08, 2017, 07:24:44 PM »
I have both the mechanical and an electric pump (via a by-pass line) connected, and my glass bowl is also never full, except as previously noted during first start up. I think this is as a result of some of the fuel receding and 'back' filling the glass once the engine is shut off and sits for a while, (as it is always nearly empty at the conclusion of the previous trip). As Jose correctly noted, a half full glass is about the best to expect though with my vehicle it is even less. I as well wondered what sort of pressure would be required at the pump's output side to revert fuel vapor back to a liquid for the carb to use. Anyone know? See how your car drives John, and if OK, then do as the old adage says, "If it ain't broke don't fix it"! Clay/Lexi
« Last Edit: November 08, 2017, 08:02:15 PM by lexi »