Alpha 1 Gen 2 water pressure or flow?

ghunttwo

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I checked the Mercruiser 1 service bulletin 82-4 I found on here and was wondering if this procedure and flow amounts work for Alpha 1 Gen 2. ​I read somewhere that Gen 2 doesn't have a lot of pressure but a lot of flow. How do I determin if I have the proper flow or pressure?
My ride is a Donzi 18 Classic 2003 with a Mercruiser 350MAG MPI with a Alpha 1 Gen 2 outdrive, New water pump, SS housing, ware plate and seal.
​The Pressure is running .6 to 1 psi at idle and at WOT 5.5 to 6 psi. Also read that if High pressure on these indicate a the start of a blockage or blockage.

The question is what pressure and or how much flow is correct?
Thanks George
 
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Bt Doctur

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Ignore this
"The Pressure is running .6 to 1 psi at idle and at WOT 5.5 to 6 psi. Also read that if High pressure on these indicate a the start of a blockage or blockage.

The question is what pressure and or how much flow is correct?"
Replace the impeller at 3 year intervals, no matter what. Keep a keen eye on the engine temp.any increase is the time to investigate not when you overheating .
Stay out of the sand and mud and you`ll be just fine.
 

Scott Danforth

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The alpha pump will push just under 20 gpm. The pump deadhead pressure is about 20psi

However as Bt doctur stated, replace impeller every 3 years and go boating
 

muc

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I don't agree with the advise given above.
The O.P. doesn't give his serial number so I can't be sure, but based on the year, the fact it's an MPI motor and that he uses numbers like ".6 to 1 PSI" it is very likely he has a 555 ECM controller and smartcraft gauges.
If so, numbers this low could drop the engine into Guardian and substantially reduce it's output.
If he has a bad water pressure sensor it won't matter how often the impeller is replaced.

It's rarely a good idea to ignore gauge readings.

O.P. Yes it is correct that higher pressure than normal baseline reading can be caused by blockage in the exhaust manifolds. But first you need good baseline numbers and the numbers you posted aren't good.
 

alldodge

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An 350 MPI with an Alpha drive makes me wonder a bit. A 300 hp motor with a 300 hp max drive
 

ghunttwo

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Thanks for all the replies and suggestions. The question remains how do I check pressure or flow and how much flow . Early December we did a St Johns river toy run of about 60 miles. Yes the water was cooler then and with a new pump was running too cold. I renewed the thermostat and now runs at a steady 165". Last weekend I took it out for about 40 minutes at about 75% power and still 165". A few 5 to 7 minute WOT runs it got up to 170" then cooled down to 165 when.I went back to 75% power.
 
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Scott Danforth

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Start engine at idle with boat at dock, pull hose from outdrive to thermostat housing.

You should fill a 5 gallon bucket in under 20 seconds

Post #3 has the flow data for an alpha 1, gen 2 raw water pump
 

Scott Danforth

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or you could simply replace your water pressure sensor since they do go bad. especially if you boat in salt water.
 
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