Pressure gauge/pickup on 175xr2 SportJet

[Ben Okopnik]

Hey, all -

I've got a Rinker Rocket with the above engine in it, and have a 2-30 PSI gauge on the dash which picks up the pressure like so:



(That shiny black tubing, by the way, has dried out and turned into dust behind the panel... so that pressure has been venting to the world. I'm going to plug it off until I figure this out.)

The question is, what the heck is that pressure supposed to tell me? And - directly related to that - what is it connecting to on the engine? I've looked through the workshop manual, and can't find any mention of what that tap-off is, or what that indication means.

 

[Speedling]

Does that larger rubber hose go into the engine block or the air cleaner? If air cleaner then it is vaccum not actually pressure. If into the block my guess is coolant pressure in the engine.
Vacuum would tell you certain things about how it is running but coolant pressure, since it is on a jet, is more crucial to monitor.
Any clue as to the gauge it goes to?
Is that a hard line and turning brittle? If it was soft, i would look into 2 cycle fuel line. If brittle look into possibly something like oil pressure or boost gauge kinda line. Need to know what is passing through first though!
Looks like a compression fitting holding it on. May be able to take off and bring to hardware store easy enough.

 

[Ben Okopnik]

Does that larger rubber hose go into the engine block or the air cleaner? If air cleaner then it is vaccum not actually pressure. If into the block my guess is coolant pressure in the engine.
Vacuum would tell you certain things about how it is running but coolant pressure, since it is on a jet, is more crucial to monitor.
Any clue as to the gauge it goes to?
Is that a hard line and turning brittle? If it was soft, i would look into 2 cycle fuel line. If brittle look into possibly something like oil pressure or boost gauge kinda line. Need to know what is passing through first though!
Looks like a compression fitting holding it on. May be able to take off and bring to hardware store easy enough.

Well, the large hose goes into the engine block - but since the coolant is just raw water, I can't imagine that being tapped off via tubing to a gauge. I mean... salt water, or even bits of dirt in the fresh through that kind of tubing would clog it up within minutes, right? I'm thinking it's got to be pressure or vacuum, and since it's marked PSI (rather than, say, inHg or something), that sounds like pressure to me. I may be assuming far too much logic on the builder's part here.

The gauge is this kind of thing (the little symbol also seems to imply "pressure"):




And the line is this:



I'm guessing that's 2.5mm ID - just a hair over 1/8". Fairly hard but flexible, like the poly tubing used for plumbing nowadays, so it could carry either vacuum or pressure. Based on where on the block that that thicker hose is tapped off - a couple of inches crank-ward from the head gasket - the only thing that makes sense is a tap into the jacket, and thus coolant... but like I said, I can't see that working for any length of time. I'm happy to be corrected by someone who knows better, though.

Can't be oil pressure - it's a 2-banger running premix - and there's nothing like boost on it. So I'm still - as they say - at sea.

 

[Ben Okopnik]

Ah. I think I've found it - and @Speedling , you called it dead on; it's water pressure. Maybe there's a membrane somewhere in that tee fitting (turns the water pressure into air pressure?) - in any case, there was certainly nothing spraying out of that tubing, and it's not clogged.

https://www.ebay.com/itm/New-OEM-Mercury-Water-Pressure-Gauge-Kit-79-895288A21-/172906020568

What makes it especially interesting is that the Merc manual considers it a test tool - one used to troubleshoot cooling problems - where this gadget is specifically intended to be installed. Wonder when the shift happened.

Anyway, thanks much! Now I just have to learn to scan it for what's normal, and decide on what to do when it's not...

 

[Speedling]

Ah. I think I've found it - and @Speedling , you called it dead on; it's water pressure. Maybe there's a membrane somewhere in that tee fitting (turns the water pressure into air pressure?) - in any case, there was certainly nothing spraying out of that tubing, and it's not clogged.

https://www.ebay.com/itm/New-OEM-Mercury-Water-Pressure-Gauge-Kit-79-895288A21-/172906020568

What makes it especially interesting is that the Merc manual considers it a test tool - one used to troubleshoot cooling problems - where this gadget is specifically intended to be installed. Wonder when the shift happened.

Anyway, thanks much! Now I just have to learn to scan it for what's normal, and decide on what to do when it's not...

Well then basically make sure it has pressure while underway. More pressure should be present at full speed. It can also let you know if you are cavitating.

 

[Ben Okopnik]

I was initially thinking that it doesn't make a whole lot of sense to have such a gadget on the panel - the head temp gauges would show blocked cooling pretty quick - but I guess it would be an instant indication of having sucked a plastic bag, or a bunch of jellyfish, into the grate. Not critical, but certainly useful.

A bit more searching in the manual has turned up the expected pressures at that tap-off, in both PSI and (KPA):

1,000 - 1,100 in neutral 1/2 - 1-1/2 (3.4 - 10)
5,300 boat on trailer (static) 9 - 10 (62 - 69)
5,300 boat on plane 35 - 40 (241 - 276)

A bit odd that the gauge only goes to 30PSI, then...

I think I'm going to simplify this thing a bit by getting a pressure sender - lots of them on Amazon for under $20 - and a little gauge for it, or maybe even hack it into the Defi "10-in-1" display unit I'm planning to install (where it would show up as "manifold pressure".) Never was much of a fan of sending fluids all over the vessel via little fragile tubes... especially after having to clean up oil spewed from those little tubes in the old cars I used to play with.

 

[njmr2fan]

Wrong place to ask for pics of your boat?

 

[Ben Okopnik]

Wrong place to ask for pics of your boat?

Eh, probably. But here she is - I'm very proud of my little pocket Rocket (especially now that I've just finished rewiring her, stem to stern!)




This coming week, I'm replacing the panel with some nice black thermoplastic, with cutouts for a 6-gang switch/breaker combo and a Defi Advance "10-in-1" display that will replace all the tired-out, rusty gauges; I'm also installing six Scotty rod holders. Further down the road, I'll make a cubby in the starboard seat (maybe even make it a livewell?) as well as a small one below the shifter, replace the shifter with the original Teleflex/SeaSense one (and get rid of the foot throttle), and maybe swap the steering unit for a 270º one (rather than the 90º that it came with), and add one of those CobraJet steering units.

I love playing with my toys.

 

[Scottintexas]

That's quite a bow light you've installed, isn't there supposed to be a green in there??

 

[Ben Okopnik]

That's quite a bow light you've installed, isn't there supposed to be a green in there??

The green (and the red) are just below; they're those dark-looking strips just above the rub-rail. That thing above them is so I can boil the water ahead of the boat if I run across zombies, unfriendly aliens, or Great White sharks. Can't be too careful, you know.

I got to test all this stuff out last night; the LED nav lights are excellent. As to the bow light - it's a freakin' assault weapon! The fog lights are super-useful for lighting up a dark creek or the boat ramp, but those white ones... whew. I'll have to tweak them so they point down at the water more; I was spotlighting houses that were easily a half a mile away, and probably blinding the folks in them. Didn't realize just how powerful they were going to be.

Oh, and here's part of yesterday's test run:



7 1/2 lb. On that light-action rod, it was a MONSTER. Took a good 10 minutes to get him in the boat.