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Technical Liquid Filled Fuel Pressure Gauge

Discussion in 'Traditional Hot Rods' started by mwhistle, Jul 12, 2018.

  1. mwhistle
    Joined: Feb 19, 2007
    Posts: 284

    mwhistle
    Member
    from sacramento

    There have been a number of posts regarding the inaccuracies of liquid filled fuel pressure gauges. Apparently, unlike the non liquid pressure gauges, the liquid filled ones are very sensitive to atmospheric temperature and show inaccurate readings (like no pressure despite the engine running perfectly well). I've used both types of gauges and can attest to the problem. All that said, I noticed that Summit Racing advertises the Aeromotive fuel pressure gauge which is liquid filled, but includes a relief valve to ensure accuracy. These Aeromotive gauges are twice a costly ($47) as the usual ones from Summit or Earls, etc. Does anyone have any experience with these particular Aeromotive fuel pressure gauges as it relates to their accuracy. I don't mind spending the money if they are actually accurate under all driving conditions. Thank you.
     
  2. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 4,086

    Bandit Billy
    ALLIANCE MEMBER

    As previously posted, the fluid is there to stabilize the needle from vibration but it also keeps them form reading correctly at low pressure as I found out. Someone on here replaced the glyceride fluid with brake fluid if I remember correctly and it functioned better. I replaced it with a non liquid gauge with a 0 to 10 pound dial for a bit more accuracy dialing in my low pressure for my 97's. It isn't much to look at but it works very well.
    upload_2018-7-12_12-14-26.png
     
  3. I too had a liquid filled (Marshall) gauge that would not read when the engine was hot. I replaced it with a non-filled gauge and it works perfectly.
     
  4. Deuces
    Joined: Nov 3, 2009
    Posts: 15,260

    Deuces
    Member
    from Michigan

    Those liquid filled gauges are pretty much made for off road trucks and buggies... Or if you have a car with solid engine mounts and a very lumpy camshaft.....:confused::rolleyes:
     
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  5. farmalldan
    Joined: Sep 4, 2009
    Posts: 130

    farmalldan
    Member
    from Duncan, OK

    We used thousands of liquid filled gauges during my professional career with no problems. Of course, we opened the case vents per instructions after installation. You guys didn't overlook that, did you?
     
  6. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,356

    porknbeaner
    Member

    The idea behind the liquid filled gauges is that they do not fail as easily due to vibration. There is an obvious remedy to the problem, actually two depending on how high tech you want to be. The high tech solution is to get an electric and mount the gauge on the firewall. The low tech solution is to set your fuel pressure then remove the gauge and cap the T.

    Here is something to think about, you seldom set your fuel pressure once you get the pressure set. If you took the car to a mechanic and had him set the fuel pressure he would use his gauge that he took from his toolbox, set the pressure and put the gauge back in his toolbox.
     
  7. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 4,086

    Bandit Billy
    ALLIANCE MEMBER

    ^^^^I am considering doing this cuz I don't like the look of that gauge on my flathead
     
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  8. rjones35
    Joined: May 12, 2008
    Posts: 819

    rjones35
    Member

    I've got one of the aeromotive ones. It does work. I noticed the pressure was all over the place hot vs. cold when I first got it, THEN I remembered to use the pressure relief thing.
     
  9. rjones35
    Joined: May 12, 2008
    Posts: 819

    rjones35
    Member

    Not a great pic, but you can see it. Not a big deal to release the pressure valve, and I've only had to do it once, when I first set everything up. The gauge, and their regulator, have been rock solid.

    [​IMG]
     
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  10. 31 Chopped Coupe
    Joined: Aug 24, 2014
    Posts: 39

    31 Chopped Coupe
    Member

    I can relate to this subject, I bought a K&N low pressure electric fuel pump for my flathead. I used a Safety Racing glycerine filled gauge at the fuel block on the firewall and have yet to see the needle rise up off the peg, even when I dial up the pressure on the regulator. I'm going to contact Speedway and ask for a refund for the gauge and try for a better quality.
     
  11. porknbeaner
    Joined: Sep 12, 2003
    Posts: 40,356

    porknbeaner
    Member

    This is probably not the best time to mention this but when adjusting pressure you really want the regulator and gauge as close to the needle valve as possible. Sometime logistics over rides that but that is the best way to get a legitimate reading.

    @rjones35 that is a nice clean setup. :cool:
     
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  12. rjones35
    Joined: May 12, 2008
    Posts: 819

    rjones35
    Member


    Thanks!!
     
  13. mwhistle
    Joined: Feb 19, 2007
    Posts: 284

    mwhistle
    Member
    from sacramento

    There were no instructions that came in the box with either my Marshall or Earl's fuel pressure gauge. Two responders mentioned a gauge pressure relief valve. I don't see anything like that on either of my gauges. (Maybe I don't know what I'm looking for.) Can someone explain how one relieves the gauge pressure so that it reads accurately as described above by some of the HAMB responders? Thank you.
     
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  14. Boneyard51
    Joined: Dec 10, 2017
    Posts: 1,226

    Boneyard51
    Member

    We used liquid filled gauges in the Fire service with no problems, other than an occasional leak. Those were compound gauges that read vacuum and 600 pounds pressure. Might not be a liquid problem, maybe just a gauge problem. Ours were vented. There’s a lot of crap being produced across the pond now.

    Bones
     
  15. Sheep Dip
    Joined: Dec 29, 2010
    Posts: 1,566

    Sheep Dip
    Member
    from Central Ca

    [​IMG]
     
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  16. mwhistle
    Joined: Feb 19, 2007
    Posts: 284

    mwhistle
    Member
    from sacramento

    Sheep Dip, Thank you very much for picture and instruction. Even if I'm careful not to remove the plug as you suggest, won't some liquid seep out?
     
  17. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 4,086

    Bandit Billy
    ALLIANCE MEMBER

  18. rjones35
    Joined: May 12, 2008
    Posts: 819

    rjones35
    Member


    The Aeromotive one has an actual metal valve you pull up to release then push back down. Not sure about the others, other than the rubber plug that seals it.
     
  19. mwhistle
    Joined: Feb 19, 2007
    Posts: 284

    mwhistle
    Member
    from sacramento

    rjones35, Thank you very much for the explanation re: the Aeromotive gauge and relief valve operation.
     
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  20. deathrowdave
    Joined: May 27, 2014
    Posts: 1,068

    deathrowdave
    ALLIANCE MEMBER
    from NKy

    Used liquid filled gauges at work for 35 years . There are many ways around this as venting the gauge , a transducer mounted at the pressure point and a dry gauge where needed . An orifice in tap to slow the flow down will stop the wiggle in a dry gauge also and last , a pigtail curl in the tube or tap ahead of the gauge to slow flow will stop the wiggle . Vent it and forget it is best
     
  21. 36roadster
    Joined: Nov 13, 2005
    Posts: 1,676

    36roadster
    Member

    When do you vent these? straight after installation? What does the venting do, anyway? These look like glycerin filled Bourdon tube gauges, I am trying to understand why they need to vented. I always thought that rubber bung was to top-up the glycerine level. Are these supposed to have an air-gap at the top, or are they filled up completely? Thanks for the wisdom in advance!
     
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  22. rjones35
    Joined: May 12, 2008
    Posts: 819

    rjones35
    Member

    I'm definitely not the expert, but my understanding is when they get hot the fluid expands, builds up pressure and throws the reading off. I could be wrong. When the engine/fuel is hot, thats when to vent. I would assume that if they were totally full with no air gap, they would either explode, or have to be really sealed with no way for the pressure to escape,which I guess would cause other problems.
     

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