water pressure gauge

Discussion in 'Outboard Maintenance' started by el9surf, Mar 12, 2013.

  1. el9surf

    el9surf Well-Known Member

    I have a Merc sea pro 25 2 stroke.
    Do they have specific water gauges for that motor, or is there an aftermarket version that would fit on?
    I'm considering adding a jackplate to my shadowcast and have no idea if there is a gauge that is compatible or how to hook it up.

    From what I understand it's not a good idea to run a jack plate without a pressure gauge for obcvious reasons. I would like to be able to get the motor up a few inches however I don't want to cause any damage to it.

    Any suggestions?
  2. Brett

    Brett > PRO STAFF <

  3. Dillusion

    Dillusion devilray snob

    You will not cause any damage to the motor by jacking it up 'a few inches' over the tunnel's top plane. If you go 4" or more than I would say MAYBE. But with a shadowcast you wont be 4" over the tunnel's top plane.

    You dont 'need' a WP gauge...just look back at the motor and see if it's peeing a steady stream or otherwise (aerated, intermitternt, etc).

    thebrazilnut is running his merc 25 almost 5" over the bottom of the SUV17's hull plane with no water gauge and hes motor is still running strong. Last time he mentioned it, at least.
  4. lemaymiami

    lemaymiami Well-Known Member

    Every time I see another "you don't need a water pressure guage" piece of advice I just cringe.... If you ever run at night -just how would you know whether you've got enough water (unless you hear that horn go off... and by then it's too late) ?

    I've been building, rigging, etc. skiffs since the mid seventies (my first two boats I didn't have a clue...). I still won't rig any skiff without a water presssure guage.

    I'll get down off of soap box now....
  5. Dillusion

    Dillusion devilray snob

    The mercury 2-strokes from 1999-2004 and the mercury seapro he owns don't have a direct water pressure hook up to the block. The water pressure gauge needs to be spliced into the tell-tale line with a t-fitting and doesn't give a good reading.

    When operating at WOT the water pressure gauge only registers a few PSI out of the 30 or so the gauge allows. I had a WP gauge on mine, and it returned it to bass pro.

    The smaller 2-stroke motors like the 25, 15, and under dont piss hard at all, it's a larger slower low flow stream rather than a small diameter high flow hard pissing like the 40, 50, or 60 mercury two strokes have.

    I agree with your 'running at night' comment and how you can't see the tell tale...but if you're running at night chances are you have a flashlight or headlight on you, and you will be able to shine it back there if you really need to check it and are running in a sketchy area. You arent going to be running WOT in the backcountry at night...

    There is also the 'fluke' one in five-thousand chance you hit a plastic bag while out on the water...which I doubt will happen in the backcountry while jacked up. But it's not like you're constantly looking at the WP gauge every second anyway.
  6. el9surf

    el9surf Well-Known Member

    My sea pro doesn't have an alarm just for reference. Just didn't want to damage the motor by overheating it
  7. Creek Runner

    Creek Runner Well-Known Member

    I have said it and I will say it again, You don't need a water pressure gauge!

    I am a certified technician on multiple engine lines, out of the 4 current boats I own only 1 has a water pressure gauge and it's 100+ mph drag boat there is no looking back at that speed and also I'm running a low water pickup with the motor on 12" of setback and 8" high.

    I fish a lot at night, very shallow (gigging) and I have the same motor 25hp Merc on a 14' stumpknocker and I can see my water tell tale just fine without a flash light.

    I also have seen people melt power heads because they relied solely on their water pressure gauge

    lemaymiami we will just agree to disagree, as to if one is needed or not! ;)

    But like I have always said if having one makes you feel more comfortable running your engine than install one. I install them all time for customers whether or not I like/need one; it's their boat and if they need a WPG for the confidence to run then I'm happy to install it.

    Tight Lines!
  8. el9surf

    el9surf Well-Known Member

    Creekrunner, with my 25 2 stroke what PSI would I expect to read on the gauge with sufficient water flow? If it barely registers at full pressure then it doesn't seem very useful. I'm just wondering if Matty's gauge wasn't working properly, or if they truly don't produce enough pressure to register.
  9. Brett

    Brett > PRO STAFF <

    Instructions for correct installation are included with the gauge.
    Those that require a tee, it's important to properly install the tee.
    Connection to the block and connection to the gauge should be in line through the tee.
    The feed to the whizzer tube should be the portion of the tee that 90°s from the tee.
    That way you obtain best pressure results. Baseline your pressure readings
    by running with the engine at the lowest height at full speed, note the pressure reading.
    On my old outboards that was 6 to 7 psi. Raising the jackplate I could watch the
    pressure drop as more and more air entered the intake. when pressure dropped below 2-3 psi
    engine temperature would start to rise. Hitting a weed clump, or bag, dropped pressure to zero. Instantly.

    btw, installing the tee improperly, with the block and whizzer feed running straight through
    turns the 90° portion of the tee into a venturi, pulling negative pressures... :-[
  10. Snookdaddy

    Snookdaddy Well-Known Member