Low water flow from a 1991 OMC Cobra outdrive

[JCT]

I have a 1991 5.8 liter OMC engine with a cobra outdrive. The engine is over heating and I have narrowed it down to lack of good water flow from the outdrive. When I put the garden hose on the outdrive the engine runs nicely at 160 degrees. When I run it in the water, the engine quickly heats up to 200 degrees. I have replaced the impellar but not the housing. I have also replace the water intake hose located in the gimble housing. When I force water out from the hose at the thermostat housing with the impellar housing off, I get good water flow out. The intake screen seems to be clear. You should also know that last year my out drive was repaired and the propellar shaft was replaced. Not sure if this would impact the water flow at all; but I thought I would post it anyway.
Short of taking the outdrive apart to see if there is any obstruction between the upper gear housing and the intake screen I don't know what else to do.
Thanks for any help you can give.

JCT

 

[JCT]

Re: Low water flow from a 1991 OMC Cobra outdrive

When I replaced the impellar, I got the repair kit which comes with the plate and gasket so those are new. When you mention o-rings are you talking about the ones behind the adapter plate? If so how would it suck air if the whole thing is under water?

 

[a70eliminator]

Re: Low water flow from a 1991 OMC Cobra outdrive

Drive not deep enough in the water bucket, or not enough volume and your getting lots of churning air bubbles also the water in the bucket doesn't give up the heat very well.

 

[Gary H NC]

Re: Low water flow from a 1991 OMC Cobra outdrive

I would pull the impeller back out and verify the shaft that turns it is working when the engine is cranked over...
This is the Cobra with the impeller on the out drive correct? should be....

And when testing water flow the drive does need submerged just as deep as when the boats in the water.

 

[JCT]

Re: Low water flow from a 1991 OMC Cobra outdrive

Just to clarify, when I have tested the water flow,I have done so both on a hose and with the boat in the water so the drive is fully submerged when I have tested in the water. I have also cranked the engine with the impellar removed to verify if the shaft is truning and it is.
Is there anything else I could be missing here. I am concerned that I am narrowing the probelm down to the lower gear housing; but I don't know enough about that part of the outdrive.

 

[JCT]

Re: Low water flow from a 1991 OMC Cobra outdrive

This water pump is located in the upper gear housing of the outdrive. Real easy to get at.

 

[JCT]

Re: Low water flow from a 1991 OMC Cobra outdrive

This is the correct outdrive. The kit I got included part # 22, 23,24, 25 and 26. These parts have all been replaced. The old impellar I removed was still in pretty good shape. I picked up part # 30 today to see if that may be the problem but I won't get up to the boat to try it until Thursday.

 

[BF]

Re: Low water flow from a 1991 OMC Cobra outdrive

what about the impeller key? Is it in place? I assume it must have one of those (but I don't have an OMC)...

 

[Gary H NC]

Re: Low water flow from a 1991 OMC Cobra outdrive

what about the impeller key? Is it in place? I assume it must have one of those (but I don't have an OMC)...

No key on a OMC....it has a V shape to the water pump drive shaft.

 

[JCT]

Re: Low water flow from a 1991 OMC Cobra outdrive

Bad news. I replaced the water pump housing and there is no change. I still get very little water flow from the outdrive. My last test was with the boat in the water but still on the trailer so I could see the water pump in action. During this test I noticed a couple of things. One is that the water pump housing was getting warm. There other is air coming out of the tube that leads from the pump housing down to the lower gear gase.
Starting to get really frustrated so any help would really be appreciated.

 

[VMAX]

Re: Low water flow from a 1991 OMC Cobra outdrive

Hope I can help. I've got a lot of experience with this one.
#1 When you say the outdrive was in the water with the boat on the trailer, was the pump housing submerged? I needs to be.
#2 When you say air was coming from the tube going from the pump housing
down into the drive, where did you see the air escaping? Older Cobras don't even have this tube, and it's not necessary. If the tube clogs, you will have the same problem. Also, having the tube off allows a stream of water to be seen "leaking" from under the large outer cover when running on muffs out of the water. This is your assurance that the water is getting to the impeller, and should be seen within seconds after starting the engine.
#3 Did you check for obstructed passages from the pick up screens to the pump? With boat out of the water, remove pump housing and impeller and hook up the muffs. Water should pour from the back of the outdrive, unobstructed.
If not, hose is too small, pressure too low, muffs not sealing to drive well enough, etc. When you lower your drive into the lake, submerging the water pump, Water pressure will push the air up the lower housing, through the pump, and out the vent hole. When the engine is started, the volume of water should be so great, that the "leak" from the air bleed is of no consequence, and the flow coming out of the hose which supplies the raw water to the engine, will resemble that of a garden hose.
Good luck.

 

[tadams]

Re: Low water flow from a 1991 OMC Cobra outdrive

I am having the same or avery similar problem. No water flow comes from the hose at the engine's water manifold end. I hitch up the muffs and remove the pump casing's cover. Inspection of the rubber impeller looks almost new. I run the hose and water pours out of the right side of the casing. I turn on the motor and the shaft spins (slowly maybe 100 rpm, not so fast I cant see the triangle head). I unhitch the hose from the muffs and stick it down the hose at the water manifold and water comes pouring out of the left side of the pump's casing. This tells me there is no blockage. Why isn't the impeller pushing the water to the engine's water manifold? Inpection of the hose between the pump and the transom looks good and water isn't coming out any where it shouldn't. I am perplexed by why I would not get any flow to the engine if the shaft is spinning and the impeller looks good.

 

[JCT]

Re: Low water flow from a 1991 OMC Cobra outdrive

I finally got the flow problem fixed on mine and it was in the lower gear casing. Apparently the seals were damaged and thus exhaust gas was being sucked into the water passage. To fix the problem the lower drive has to be separated from the upper housing. I just gave it to the mechanic at our marina to deal with. Cost me less than 500 bucks and now I have excellent water flow.