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Old 07-19-2009, 08:42 AM
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SWeaver SWeaver is offline
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1987 Prostar Engine Leak

Hey guys, be gentle, first-time newbie on here.

1987 Prostar. Engine starts easily and idles well, runs well....but lots of water in oil. here's what happened, as best as I can tell.
Impeller shredded, boat started to overheat, but I shut it down and let her cool, restarted and went to dock. Overheat obvious because of impeller's demise, but the oil/water issue is being addressed.
Intake/exhaust/heads seem to be the consensus of where to look (I researched before posting). Are there any subtle difference in symptoms that might steer me towards one manifold over the other. It is the Chevy block with the powerslot trans. Like I said, boat will run well if I changed oil and put it in lake. Starts and runs ok in driveway w/fake lake...but the water gets in the oil.

If I remove exhaust manifold, what am I checking for? Same with the intake. Am I just replacing the gaskets, or am I somehow checking the actual manifolds? If not the intake or exhaust manifolds, I guess I'd check the Head gasket, but wouldn't that show up with a compression test or some other way before tearing into it?

Any advice would be great! Thanks!!
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Old 07-19-2009, 09:26 AM
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Quote:
Originally Posted by SWeaver View Post
Hey guys, be gentle, first-time newbie on here.

1987 Prostar. Engine starts easily and idles well, runs well....but lots of water in oil. here's what happened, as best as I can tell.
Impeller shredded, boat started to overheat, but I shut it down and let her cool, restarted and went to dock. Overheat obvious because of impeller's demise, but the oil/water issue is being addressed.
Intake/exhaust/heads seem to be the consensus of where to look (I researched before posting). Are there any subtle difference in symptoms that might steer me towards one manifold over the other. It is the Chevy block with the powerslot trans. Like I said, boat will run well if I changed oil and put it in lake. Starts and runs ok in driveway w/fake lake...but the water gets in the oil.

If I remove exhaust manifold, what am I checking for? Same with the intake. Am I just replacing the gaskets, or am I somehow checking the actual manifolds? If not the intake or exhaust manifolds, I guess I'd check the Head gasket, but wouldn't that show up with a compression test or some other way before tearing into it?

Any advice would be great! Thanks!!
You have an '87 with a Chevy motor? Is it the big block motor?

If you have water getting into the oil, it's not the exhaust manifolds. Running it with water in the oil isn't a good idea, even for a short time.

Do a compression/cylinder leakdown and vacuum test.
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Old 07-19-2009, 07:03 PM
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It's a GM/Indmar 350 small block with powerslot tran.

If it is an intake gasket/manifold or head gasket, are the car ones the same or do they need to be marine specific. I know most things are marine specific, but not sure about gaskets or manifold.

Thanks.
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Old 07-19-2009, 08:47 PM
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Originally Posted by SWeaver View Post
It's a GM/Indmar 350 small block with powerslot tran.

If it is an intake gasket/manifold or head gasket, are the car ones the same or do they need to be marine specific. I know most things are marine specific, but not sure about gaskets or manifold.

Thanks.
Marine gaskets only.
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Old 07-19-2009, 09:42 PM
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Thanks for the gasket info, JimN.

Would you suggest the line to the carb to tap into, or is there someplace better off the intake manifold for the vacuum test?
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Old 07-19-2009, 10:33 PM
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Originally Posted by SWeaver View Post
Thanks for the gasket info, JimN.

Would you suggest the line to the carb to tap into, or is there someplace better off the intake manifold for the vacuum test?
Look for a rubber cap on a fitting below the throttle plates, at the rear of the carb. It has to be taken from below the throttle.
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  #7  
Old 07-20-2009, 11:21 AM
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I tapped the line off the valve cover to the back to the carb and it read a steady 12" at idle. I'm going back to do a compression test, but that reading suggests an intake manifold problem, right?
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Old 07-20-2009, 12:56 PM
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the compression test ran cyls 1-8 as follows
172/180/163/175/160/162/170/165 for a low to high rangeof 160-180.
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Old 07-20-2009, 01:11 PM
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So its not a head gasket.

I'd pull the intake to see if you can find where the water is coming from. Also, I wouldn't leave the oil/water mix in the engine for too long.
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  #10  
Old 07-20-2009, 01:12 PM
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sweaver, fyi, your engine is probably not the original one because as far as I know, all 87s came with Ford 351 Indmar engines. that is why JimN asked about it too. I had an 87 for a while. however, I do not know for absolutely sure. Jim should be back to comment on compression test data but they look ok to me. the lowest cost issue would be a bad head gasket but you could have a cracked block. good luck.
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