496 Mag locking up

MrLean

Recruit
Joined
Sep 1, 2020
Messages
2
Bought my 2004 Formula 34 PC 7-8 weeks ago, boat has run great. 225 hours when I bought it, 270 now, always fresh water.

Boat sat for a week, came down to marina, it started right up like normal. 30 min run across the lake, dinner for 2 hours, come out and starboard won't start. Turn key, nothing. I know the batteries are old (was going to replace this winter), so I flip the battery parallel switch. Still nothing, and then the starter starts whirring like it won't engage. Go home on one engine. Mechanic goes down and replaces starter, boat still won't start, engine is locked up. He "puts a breaker bar on it" and gets it to turn over a few times, slowly. Says he "should hear air puffing out when he turns it by hand, but thinks he hears squirting noise like water squirting out". After he turns it over by hand a few time and lets it sit for a couple minutes, he's able to start the engine like normal.

They are going to go down and pull the plugs today after letting the boat sit overnight to see if there is water or antifreeze in any of the holes.

Previous owner owned the boat since 2005, but has only put about 25 hours on it from 2016-2019. I know he had the impellers done last August, and my mechanic is the same one who did the work, claims they were replaced due to an overheat.

What should I look for in each of the following situations:
1. water in the plugs
2. anti-freeze in the plugs (unlikely since the antifreeze is full)
3. nothing in the plugs

Anything else I should look out for, or ask?
 

alldodge

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Mar 8, 2009
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43,294
Pull all the plugs, then pull the main power relay, then use starter to crank it over. WIth the MPR pulled the fuel pump or the ECM will not be powered up
 

Bondo

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Apr 17, 2002
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Mechanic goes down and replaces starter, boat still won't start, engine is locked up. He "puts a breaker bar on it"

Ayuh,...... Welcome Aboard,..... You need a new mechanic,..... That guy is gonna co$t you a big bundle of money,.....

He shoulda pulled the spark plugs, before he broke out the breaker bar,.....
'n if he used the crankshaft bolt, he's gonna ruin yer motor,......

I'd check the spark plugs to tryin' Id the water, if it's lake water, pull the risers off the manifolds, 'n inspect the gaskets, 'n sealin' surfaces of both,.....
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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Jul 23, 2011
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51,316
First, welcome aboard

Bought my 2004 Formula 34 PC 7-8 weeks ago, boat has run great. 225 hours when I bought it, 270 now, always fresh water.

Boat sat for a week, came down to marina, it started right up like normal. 30 min run across the lake, dinner for 2 hours, come out and starboard won't start. Turn key, nothing. I know the batteries are old (was going to replace this winter), so I flip the battery parallel switch. Still nothing, and then the starter starts whirring like it won't engage. Go home on one engine.

Previous owner owned the boat since 2005, but has only put about 25 hours on it from 2016-2019. I know he had the impellers done last August, and my mechanic is the same one who did the work, claims they were replaced due to an overheat.

per VP, impellers are to be done every other year.
things that will hydro-lock your motor:
Water soaked hull, thus lowering the riser to SWL dimension
overloaded hull, thus lowering the riser to SWL dimension
leaking manifold joint or cracked manifold from rust, salt, or severe overheat.
leaking head gasket from an overheat.


Mechanic goes down and replaces starter, boat still won't start, engine is locked up. He "puts a breaker bar on it" and gets it to turn over a few times, slowly. Says he "should hear air puffing out when he turns it by hand, but thinks he hears squirting noise like water squirting out". After he turns it over by hand a few time and lets it sit for a couple minutes, he's able to start the engine like normal.

They are going to go down and pull the plugs today after letting the boat sit overnight to see if there is water or antifreeze in any of the holes.


Anything else I should look out for, or ask?

ask for a new mechanic. As bondo stated, putting a breaker bar on it is a good way to FUBAR the crank on a GM engine. since this is the same bozo that did not look further into the over-heat, I would question the shop owner about him.

he should have pulled the plugs, turned it over with the starter to get the water out, then got the motor started immediately to dry it out. Then looked for the source of the water.
 

muc

"Retired" Association of Marine Technicians...
Joined
Jul 7, 2004
Messages
2,256
Ayuh,...... Welcome Aboard,..... You need a new mechanic,..... That guy is gonna co$t you a big bundle of money,.....

He shoulda pulled the spark plugs, before he broke out the breaker bar,.....
'n if he used the crankshaft bolt, he's gonna ruin yer motor,......

I'd check the spark plugs to tryin' Id the water, if it's lake water, pull the risers off the manifolds, 'n inspect the gaskets, 'n sealin' surfaces of both,.....

Oh Ya
X3
 

MrLean

Recruit
Joined
Sep 1, 2020
Messages
2
OK, fired the old mechanic and had the one I trust (3 hours to his shop on one engine) look at it. He can't replicate the problem. Boat starts fine. Ran it, let it sit, still starts fine. Repeated this process 3x. WTF lol
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,316
measure your SWL to riser dimension
 
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