Low flow out of pump / impeller OMC cobra

[HutchOven]

This is a 1986 FourWinns 4.3l with Cobra outdrive. I recently swapped my outdrive. Every thing seemed to go together Ok but I have very low flow at the water housing. Before when I would hook up the ear muffs I could easily tell a difference after turning the boat on to see that it's sucking up water. Now it looks like it's doing nothing. I took a short video of the water inlet showing the flow with the ear muffs hooked up now.

http://youtu.be/qzQgLyHP82o

I pushed water back through this same inlet hose to back flush and maybe clear up something stuck, but no luck. Where should I start to look? I'm thinking it has to be something in the outdrive because I had no overheating issues before and now the engine gets to 200 degrees after only a minute or 2. I also just put a new impeller on it.

Thanks for any help.

 

[southkogs]

Welcome aboard.

Did you check/replace the impeller in the new outdrive? That'd be step #1

 

[HutchOven]

Yes. At the end of my first post I mentioned replacing the impeller. I replaced with everything that comes in a repair kit.

 

[John2037]

There is a water connector on the shield that commonly cracks when the drive is left always up, if it overheats sitting in the water then its not this -when youre on plane or on muffs it'll suck air - http://www.sterndrive.info/id10.html #20 is the oring for it

 

[HutchOven]

Ok so next step is to take it to the lake to see if it overheats. If it is the #20 oring, it looks like its a PITA to change. Is it?

Also I did submerge the lower half of the drive into a bucket. It was only just deep enough to submerge all of the lower intake holes and prop but no higher and it still overheated. Could this be enough to rule out the oring? I'm assuming not since you said it can suck air on plane also.

 

[Idlespeedonly]

The O-ring that John is talking about is on the pressure side if the pump. not the suction side. You said you put a new impeller in it. Did you use a new liner and a new housing?

It kinda looks like a restriction somewhere to me since in the video there doesnt appear to be any air bubbles coming out with the water. Although the video is pretty short. You can leave the big triangular cover off to see if the water pump is leaking.

The last possible cause could be the intermediate tube that connects the lower and upper water passage. It could be letting air in.
These cobras will generally not run reliably in a bucket. You really need to use muffs with water turned on full open. So you may need to check the impeller again.

 

[Lou C]

On the water hose you are not going to get a true test of the impeller, you would have a better idea of how much its pumping if you back the boat in the water, lower the drive so it primes and disconnect that hose from the transom to the thermo housing have some hold it up when you start the engine. You should then see a 2-4" head of water.
When I do the impeller, I check two things:
1) water flow from the water intakes up to the impeller mount. Hold the muffs tight to the lower unit and have someone turn on the water. With the impeller housing off, water should spurt out of the right side opening in the impeller mount in the pic above. If not there is a blockage in the water intake area, or bad water tube seals in the drive. I had barnacles causing this problem, that's why I had to learn to split the drive.
2) water flow from the thermo housing to the transom. With the hose to the thermo housing disconnected, put a water hose it it and have someone turn on the water while you look at that opening on the left side of the impeller mount. Water should spurt out. If not there is a blockage in the transom hose, PS Cooler, or the line from the cooler to the thermo housing. Also check that plastic fitting in the pivot housing (can only check it with the drive off, but if it leaks during this test that tells you something too)......

 

[Lou C]

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[Lou C]

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here's the pic.....

 

[Lou C]

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[Lou C]

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This new software is horrible....almost enough to make me quit posting here....what a waste of time.....

 

[HutchOven]

Thank you for the replies Lou. I don't see a pic, but maybe it's just my browser.

 

[Bulbash]

I had a similar issue when the rubber pieces on the water intake tube were old and cracked. Split upper and lower outdrive units and replace seals on the watertube. It solved my issue. Here is a link to the water seals I'm talking about.