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water pressure guage help

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Old 08-05-2007, 07:41 PM
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Default water pressure guage help

I am installing Livorsi mechanical water pressure guages on my engines. Merc thermostat housings, but no thermostats. Water pickup through Bravo drives with LWP pickups. Stainless Marine strainers and recirculating pumps. CMI headers and tails dump water at the tips outside the transom.

Where is the best location to tap for water pressure? Engine block? Sea Strainer?

Since the sea strainer is on the suction side of the raw water pump, wouldn't it read negative pressure?

What is a "normal" water pressure range for each location?

How should engine rpm and speed influence the reading?

Any input and experience appreciated.
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Old 08-05-2007, 08:08 PM
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We have our gauge in the engine block, and WOT reading should be 20 to 25 psi.
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Old 08-05-2007, 08:24 PM
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best place is in the water crossover on the front of the intake manifold. but you would have to drill and tap to get it there.. I have mine in the stock Merc thermostat housing, but I don't have the alarm sender so I have a free hole for the pressure gauge. You still should have a free plugged hole there that you can use.

speed of the boat will raise the pressure, along with drive trim, and of course the rpm. Mine sits on zero at idle. If I rev it up to 2000 sitting in neutral, it goes to 6 lbs. You can watch it change as you trim it.

15 lbs is plenty. Mine runs 10-12 and 130* with no thermostat, just a Moroso restrictor. 20-25 is the max that I would run. More than that and you will need reliefs or you will start blowing gaskets.
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Old 08-05-2007, 08:35 PM
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Old 08-05-2007, 09:08 PM
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Didn't see you on Saturday. How did that problem turn out?
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Old 08-05-2007, 11:13 PM
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best place is in the water crossover on the front of the intake manifold.
What if the intake manifold has a bypass port? Would that work, or tee-ing into the bypass hose if it's there?
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Old 08-05-2007, 11:38 PM
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Here is a pic where I pit mine. Just tap a 1/8npt into the manifold where I did. I put a 90 on it and painted it black. If you put it in the manifold.....it will not stay clogged up like they do in the bottom of the block.
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Old 08-05-2007, 11:48 PM
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What if the intake manifold has a bypass port? Would that work, or tee-ing into the bypass hose if it's there?
I assume you are talking about the hoses we run on intakes from front to rear? Where that front hose goes in, is the passage that you want to be in. I don't know if it would cause any problems by "T'ing" into that line or not. It would seem to be a great way to get past drilling the intake again.
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Old 08-06-2007, 12:50 AM
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Forgive my ignorance...I've got Mk IV 454MAGs running stock GM aluminum manifolds. There's a bypass hose that runs from under the thermostat opening down to the circ pump.
I'm no t-stat housing expert by far, but it seems like PSI readings would depend where you mounted the sending unit; closer to the inlet hose you get a reading from the raw water pump, not PSI in the block. Or if you tap into it "above" the t-stat, still not quite accurate?
Sorry Red Dog for hijacking Hopefully the info is worth something to you, or somebody else that might be reading
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Old 08-06-2007, 02:47 AM
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You should take your readings from the engine block and if you don't have at least 20 psi at 4000 rpms you run a serious risk of blowing head gaskets from gathering steam pockets. If you have more than 35 psi at 4000 rpms then you should bleed off some of the water pressure. I hope this helps you.
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