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SWeaver
07-19-2009, 09:42 AM
Hey guys, be gentle, first-time newbie on here.:o

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!!

JimN
07-19-2009, 10:26 AM
Hey guys, be gentle, first-time newbie on here.:o

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.

SWeaver
07-19-2009, 08:03 PM
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.

JimN
07-19-2009, 09:47 PM
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.

SWeaver
07-19-2009, 10:42 PM
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?

JimN
07-19-2009, 11:33 PM
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.

SWeaver
07-20-2009, 12:21 PM
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?

SWeaver
07-20-2009, 01:56 PM
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.

denverd1
07-20-2009, 02:11 PM
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.

mayo93prostar
07-20-2009, 02:12 PM
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.

SWeaver
07-20-2009, 02:18 PM
Thanks for the reply. I'm hoping it's an intake manifold gasket, but I can't find any data on compression or vacuum to check against what I tested.

To summarize, all cylinders were 160-180psi, the vacuum was 12. There is water in the oil, and no other symptoms. Can't seem to find a cylinder leak tester around here, but wouldn't the compression test rule out a head gasket?

SWeaver
07-20-2009, 02:22 PM
PS- I drained the oil and replaced it with new right after I noticed the water in it, and put a new filter on also. I figured the compression test would cycle it around and get the watery oil moving out. I'll change it again once I fix the issue that caused it.

SWeaver
07-20-2009, 02:33 PM
Actually, I just rechecked the engine info. The 350 chevy was a $630 upgrade option according to the original owners manual that came with the boat. There also were 2-454 upgrades, a regular and a high output.

SWeaver
07-20-2009, 03:44 PM
So, about the vacuum test.....
I don't have any other line except one that goes to the PCV valve. To use this line, would I Tap into it or hook it up directly and leave the PCV unconnected to get the accurate diagnosis?

87MC owner
12-06-2009, 10:08 AM
As far as I know, all 87s came with the Indmar 351. The option to that engine was the powerslot transmission.