1986 gm omc sterndrive 3.0L Water pump impeller question?

BruceWayne

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I recently purchased this boat and was told it had water in the oil and probably had a cracked block. Since I'm out of work and had the time I thought I would try to fix it with zero experience with marine engines! So I drain the oil and water and put oil in it and changed the spark plugs, hook up the water and charged the battery and cranked over the motor. It turned over just enough to let me know it was not seized up. However I discovered there was no water making it up to the engine. So I tried flushing it out from the hose to the water pump(out drive), then past the thermostat into the exhaust manifold. Thinking it might be plugged up, no luck. I just got the water pump off and when I inspected the impeller, it looks pretty good(no cracks, little wear).
So now where do I go? The key is in the shaft holding the impeller in place. When I ran the engine the prop moved when I moved the shift in the forward position. I did lubricate the cylinder walls before I turned the engine over and eventually ran it for a short period of time.
A lot of information, but hopefully enough to get some good advice! Appreciate any help, kids are begging me to fix this boat. So that is my story!

thanks
brucewayne
 

jerryjerry05

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Fill out the profile U might be close to someone who can help.
If U have it apart replace the impeller.As far as running it on the hose U need a good bit of pressure to make it work right.Take it to the lake or get a big bucket.The water should be at or above the impeller housing.
Once U start it,remove the hose from the drive at the thermostat housing.It should push a lot of water at idle.Try that and report back.Jerry
 

Howard Sterndrive

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

So I tried flushing it out from the hose to the water pump(out drive), then past the thermostat into the exhaust manifold. Thinking it might be plugged up, no luck.

no luck meaning you couldn't get water through the engine?
no luck meaning you couldn't get water to flush backwards through the drive?
or
no luck meaning the water flushed through fine and so you don't know why it wasn't flowing on muffs.

1986 Cobra? or 1986 400 Series?
 

BruceWayne

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Fill out the profile U might be close to someone who can help.
If U have it apart replace the impeller.As far as running it on the hose U need a good bit of pressure to make it work right.Take it to the lake or get a big bucket.The water should be at or above the impeller housing.
Once U start it,remove the hose from the drive at the thermostat housing.It should push a lot of water at idle.Try that and report back.Jerry

Thanks Jerry,
That sounds like a good ideal, can I attach a photo of the existing impeller and you might think it would be okay to use it to run the test. I believe it will not be that difficult to reassembly to test once I purchase some bolts that snapped off when I took it apart! Yeap, only 4, but I've gotten 3 tapped out so far. Does the water pump on the engine have any part in drawing the water up to the thermostat? I will wait until I hear from you before I attach any photos.
Thanks again
brucewayne
 

BruceWayne

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Yes I did get water to pass through the hose that goes to the thermostat back to the intake above the prop. I did notice water coming out above the intake where I think the water comes out at the exhaust manifold. When I ran water throught the hose going out of the thermostat, it seemed to flow pretty good. The drain fitting on the manifold was a little clogged, but I flushed it out and it now seems fine now. It is an 86' 400 series. I did't mention earlier that I became aware of these things when I did't notice water shooting out at the outdrive when the engine was running. It was at this point that I checked the thermostat for water and found none. Sorry if I'm not explaining things well, I'm doing the best I can.
Thanks for your patience.
Thanks Howard Sterndrive
 

CobiaXL

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

check splines on the water pump shaft.....inside and out
 

BruceWayne

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

check splines on the water pump shaft.....inside and out

They seem to be in good shape, I just took pictures, I will attach photos. Let me know what you think! .#
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Lou C

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Definitely NOT a Cobra, must be the last of the Stringers, on the Cobra, there is a test for the impeller, where you put the boat in the water, disconnect the raw water intake hose at the thermo housing and hold it up while someone starts the engine briefly. It should send a stream of water up at least 2-4 inches high, if 2 or less the pump is not pumping enough volume of water. The Stringer is probably similar, other areas to check are the wear plate, housing, water tube seals, etc. The impeller in the pic does not look worn...
 

BruceWayne

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Definitely NOT a Cobra, must be the last of the Stringers, on the Cobra, there is a test for the impeller, where you put the boat in the water, disconnect the raw water intake hose at the thermo housing and hold it up while someone starts the engine briefly. It should send a stream of water up at least 2-4 inches high, if 2 or less the pump is not pumping enough volume of water. The Stringer is probably similar, other areas to check are the wear plate, housing, water tube seals, etc. The impeller in the pic does not look worn...

Is the wear plate the impeller plate, if so, I did notice it does not have the curve that the manual shows, but does seem to be relatively flat. The manual says that is okay. I did try running the engine with the intake hose to the thermostat off to test it, but did not get any water at all!
 

BruceWayne

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Thanks Lou C
I'm hoping to put it back together and run some more test. I'll report what I find.
 

BruceWayne

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Feb 4, 2011
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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Just one more thing Jerry, when I drained the gear oil from the outdrive it was creamie coffee color from the bottom and more dark brown from the top. I put all of it in a clear container and so far after several days, there is less that an oz. of water floating on top. Could the water be from condensation, from the boat sitting outside for the last 3 years?
 

Gary H NC

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Water in the gear lube is a different problem.It is not from condensation.

As far as the impeller,does the shaft turn when cranking the engine over?
 

BruceWayne

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Re: 1986 gm omc sterndrive 3.0L Water pump impeller question?

Water in the gear lube is a different problem.It is not from condensation.

As far as the impeller,does the shaft turn when cranking the engine over?

Gary H,
Bummer about the condensation question. As far as I know, I would say yes, because the prop moves some when I had it running at idle.
 
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