TomZ

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TomZ

iTrader: (2)

On my new 311 I've run into an issue with water pressure. While out in some 4-footers running about 50, I noticed the water pressure on the port engine swinging pretty wildly (expected since the pickups were coming out of the water), and when we slowed, she became a little more manageable. We took a break and came off plane... opened the hatch to find that the circulation pump hose was cut by the belt. Bilge pumps on... headed in. Fortunately, I had a replacement hose from my 454 at home so no big deal there. I replaced it, and adjusted the hoses to give me clearance to the belt.

Further reading indicates I've got a water problem to solve. Before diving into a bunch of potential fixes, I'm going to look at the thermostat housings to see if there are any blockages happening, but I'm curious about how to attack this issue if I do not find a restriction. The starboard engine runs at about 25 lbs max. The boat is a TRS set-up with the factory transom pickups (I don't think there's a need to adjust because they've been there for years). If I need to bleed off pressure, can I take care of this at the sea strainer, or does a valve need to be installed between the ram water pump and the thermostat?

Thanks!

TomZ

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Additional info... exhaust is a set of CMI E-Tops that run cold to the touch so water seems to be flowing well there. Engine temps hold a steady 180 degrees, both sides. Both engines showed belt rub. Max pressure on the starboard engine is 25 lbs.

airjunky

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I would say at 25 , there is not much margin for increased pressure down the road..easiest way i can think of is take pressure readings between water outlet and headers. Sometimes flakes of rust can get in there and block water flow.still unloads enough to cool exhaust
If your measuring at the intake front crossover , you already know what you have under the thermostat

TomZ

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Speaking with the original owner, he says he never knew of the pressures being high until he redid the dash (added water pressure gauges). It's been running a few years like this, and there's no idea if this happened after the 502's were installed or if it was an issue with the 420's.

I've been searching for relevant info within OSO, and some have made the assumption that the new style thermostat housing (used on the 454 and 502 MPI) may be to blame. Regardless, that's something that I want to get taken care of.

On a side note... I understand now why one would plumb a pressure relief valve into the sea strainer: to relieve pressure spikes caused by the boat leaving the water and its reentry (I was seeing this when we were out in the rough going from the 'Bay into the Atlantic... we were having some fun!).

I'm going to look over the exhaust this weekend to see if anything is clogged. All four pipes run cold to the touch, but again that isn't necessarily saying anything. I'm taking my pressure reading from the thermostat housing.

airjunky

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Running electric senders or kicking it old school and plumb 2 lines all way to the dash ? Either way there is often a limited life span of those remote water pressure gauges.
But it is for sure nice to have

TomZ

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They're mechanical gauges that are plumbed all the way to the dash.

airjunky

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I have a few electric ones i use for stuff like that and tee them in , matches oil pressure ohms , then just run temp wire to oil pressure gauge , lets you watch pressures at wot without being in the engine compartment. Best on big boats. And hot , up to tempature water lines lol