OMC Cobra Impeller Replacement

[Jerry San Diego]

I am a new boat owner and a first time post to this forum. I have a 1988 Bayliner Trophy 21ft. It has a 3.0L OMC engine and a Cobra stern drive.<br />Just bought the boat and thought I would replace the impeller as a precaution. Replaced the impeller as directed in the manual. Now it does not appear that the impeller is working properly. No water discharge from the propeller and the Impeller housing is very hot to the touch. I carefully installed all the parts ensuring the gaskets and o-Ring were in place and tight. Is it possible that the impeller has lost its prime? I have the flush attachment hooked up and water turned on. How can I make certain that the impeller is working correctly? Thanks for any help.

 

[Lou C]

Re: OMC Cobra Impeller Replacement

Make sure that the vanes of the impeller face in the direction shown in the manual, also make sure the metal "cage" is secure in the housing, and the vent hose that goes from the housing to the hole in the upper surface of the outdrive has to be clear, that helps the pump prime buy expelling air. If the housing got that hot, you should probably replace it, they are plastic and are easily distorted by heat.

 

[Jerry San Diego]

Re: OMC Cobra Impeller Replacement

I will double ckeck vane direction and vent reassemble and try again. Thanks for the help.

 

[Lou C]

Re: OMC Cobra Impeller Replacement

Are you using an OMC manual?? they are pretty good on details. Make sure you have good water pressure to your muffs, and make sure they fit well, the cheap ones do not. I use the Tempo dual inlet ones, much better. Once you get it running, keep an eye on the temp gauge. One way you can tell if it pumping is the temp of the thermostat housing and the manifolds. The manifolds on my Cobra are cool at idle, and the t-stat housing is hot where the big hose that goes to the engine water pump connects, but cool where the hoses that connect to the manifolds connect. In the manual it says you can check flow by warming up the engine, shutting it off, and disconect the hose going from the outdrive to the thermo housing. Have a helper hold up the hose so you can see it, and start the engine (just for a couple of secs, don't forget now it is not getting water so shut it right off) and you should see a stream shoot up about 2" out of that hose if you have good flow. Cobra impellers are actually pretty easy to do.

 

[Jerry San Diego]

Re: OMC Cobra Impeller Replacement

Thanks again for the info Lou, It was too hot today to try to reassemble and work on the boat. I will do it tomorrow. I did check and the impeller vanes are turned the proper direction. The housing does not look like it was distorted at all. I am using a Cobra Manual- by Selco (sp). I bought a new set if muffs for the water a dual flo type. Do you know if with the housing off should I get water to the impeller mounting area if I turn the water on to the muffs with the impeller housing off just to see if water is flowing up there without running the engine? Also is it possible to have too much water pressure at the muffs that will effect the water flow to the impeller? Thanks again.

 

[Lou C]

Re: OMC Cobra Impeller Replacement

Yes I think if you run the water to see if it is getting up to the passage in the water pump housing you will see water come out there. I don't know if you can have too much pressure, I always run the hose on full pressure when I run mine on the hose. Only time I had a problem is when my wife ran the wash, all the sudden it is running hot, I shut it off, wait a while, start it, its fine, then starts running hot again, shut it off, and go in the basement and I see the clean laundry!! That episode of hot running (engine was not pegged, but at about 190) warped the plastic thermo housing, the metal cage shifted, and cut into the impeller (just took a chunk out of it). I replaced all the parts, also you have to make sure that you use OMC gasket sealer on the gasket for the water pump housing, it has to be air tight or else it may suck in air, and will not pump water.

 

[Jerry San Diego]

Re: OMC Cobra Impeller Replacement

When I bought the impeller kit the person sold me something called Bellows sealer to use, is that the same thing as OMC Gasket sealer. Will An automotive gasket sealer work also? I will work on the boat today- Also my cages does not appeared to have shifted and the impeller still looks good. Thanks again.

 

[Lou C]

Re: OMC Cobra Impeller Replacement

Not sure if it is the same stuff, the OMC gasket sealer stays pliable, does not get hard. You can get it at dealers selling Johnson/Evinrude motors, they still sell OMC parts. You could ask George Van Parys over at www.boatered.com about that, he will know if it is OK to use.

 

[Jerry San Diego]

Re: OMC Cobra Impeller Replacement

Lou:<br />Thanks again for you assistance and the new webb site. I have double checked the impeller housing and decided to go with your previous recommendatino and replace the housing also just to be safe. Look like it may have gotten hot enough to melt a littli of the inside of the impleler housing and allowed the cage to spip just a little bit. So am going to get a new housing today and also will just go ahead and get some OMC gasket sealer at the same time. My new muffs are the tempo type- I noticed that they have to nee exactly over the intake holes and I have to make sure they are tight. When I hook them up with the Impeller housing off water did go up to the bottom if the impeller housing inlet side. Also I noticed the water drain plug that was under the decal on the port side is leaking because I notice rust stain coming from the area. Pulled out the plun and was suprized to see the nut was missing. Was able it fish it out of the cacvity, but putting it back i was a challange. No way to hold it while screwing the plug in. But I was able to get it by taking a couple of small piecies of dental floss, putting it thru the nut and bringing it back outside to pull the nut tight enough to get the screw started again. Will get new seals and O-Ring for it today also and retry the same thing- Hope I can fish the nut and back plate back out again.<br />Thanks again

 

[Lark40]

Re: OMC Cobra Impeller Replacement

Looks like you learned the hard way about that "do not touch" plug on the Cobra port housing. Most of us made that mistake also.<br /><br />You were very lucky to get the retainer back in place without having to pull the sterndrive.<br /><br />Anyway, I am responding to the question about hose water pressure to the muffs. I have always heard/read never to run full hose pressure, rather to get a decent flow at about 1/4 turn. The reasons for not running a higher hose flow include blowing out seals and re-positioning the impellor blades. Makes sense to me.

 

[Jerry San Diego]

Re: OMC Cobra Impeller Replacement

Thanks for the info regarding the hose pressure. Makes sense to me also now that you mentioned it.<br />I took all the advice Lou gave me and replaced the Impeller housing today. Also successfully replaced the seal and O-Ring around the untouchable water drain plug, which I never intend to touch again now that it appears the leak is fixed. Guess I was pertty luck to get it in again. Now that I have replaced the impeller and all the works inside and the housing I started the engine. The housing gets pretty hot for approximately one minute then almost as if magic has occurred water starts flowing and it cools off. at the same time it starts to cool off water begins flowing from the stern drive under by what I think is called the gimble housing. I think it may be from the exhaust water I don't know. Do you know if water is supposed to come out there, and should it take a minute for it to start pumping water thru the housing where it is cool again? Thanks for any help or suggestions

 

[VMAX]

Re: OMC Cobra Impeller Replacement

Hi,<br />I have just one question for you.<br />Do all of these conditions occur with the boat in the water, or on muffs?<br />The reason that I ask, is that when the Cobra drive is down in the water, the pump is below the surface. That way, there is no problem priming the pump. With muffs on , you have to have a good enough seal and enough pressure to force water all the way up to the impeller before starting the engine. My cobra has a bleed hole in the impeller housing, and I never start it on muffs until I see a stream of water coming out. This way I have no problems.

 

[Lou C]

Re: OMC Cobra Impeller Replacement

On mine the water does come out from the gimble housing, so you are OK on that. Some Cobras have an aftermarket ex bellows that is slit on the bottom, and lets the exhaust water out there too, not out of the vents on the lower unit. I have never felt the temp on my Cobra's impeller housing at start up, so I can't say about that. But I am sure that mine starts pumping water out the gimble right after it is started, the engine and manifolds are full of water from the last run unless you drain it every time (which I doubt!!) So I would check further for a restriction, how is your engine temp on the gauge when you run it?? Should be right around 160 or so. You may want to see if you can find an OMC shop around that is familar with the engine you have and see what they say. Ultimately you have to run in the water to see if it does not overheat, so if you are close to a ramp and can just drop it in to see, it may give you a better sense of how it is. Just keep a close eye on that temp gauge!!

 

[Lou C]

Re: OMC Cobra Impeller Replacement

On mine the water does come out from the gimble housing, so you are OK on that. Some Cobras have an aftermarket ex bellows that is slit on the bottom, and lets the exhaust water out there too, not out of the vents on the lower unit. I have never felt the temp on my Cobra's impeller housing at start up, so I can't say about that. But I am sure that mine starts pumping water out the gimble right after it is started, the engine and manifolds are full of water from the last run unless you drain it every time (which I doubt!!) So I would check further for a restriction, how is your engine temp on the gauge when you run it?? Should be right around 160 or so. You may want to see if you can find an OMC shop around that is familar with the engine you have and see what they say. Ultimately you have to run in the water to see if it does not overheat, so if you are close to a ramp and can just drop it in to see, it may give you a better sense of how it is. Just keep a close eye on that temp gauge!!

 

[Jerry San Diego]

Re: OMC Cobra Impeller Replacement

Thanks for all the help and advice- I have not tried the engine with the boat in the water yet only have run with the muffs. I think I will try it in the water and see how it goes. Makes sense that if it is in the water the pump will be submerged and should be easier to prime. Also it is nice to know that water can flow from the gimble when running. I do notice water comng out of several small holes indicating that the muffs are hooked up and the water is flowing thru the lower drive.