OMC Cobra Water Pump Problems

[kevlh21]

I have a 1989 Bayliner 2755 with OMC 460. I took my boat out two days ago to the lake. Once I put it in the water my engine got really hot and the rubber manifold couplers started smoking. One coupler split and exhaust was coming out. I took it home and tore apart the water pump. The rubber impeller was toast. Today I replaced it and took it out again. Again the couplers started smoking but didnt get as hot. I took it home again and the rubber impeller was toast again! Do I need to buy the whole water pump impeller and housing or does the problem lie elsewhere? Thanks!

 

[HT32BSX115]

Re: OMC Cobra Water Pump Problems

Do I need to buy the whole water pump impeller and housing or does the problem lie elsewhere? Thanks!

Howdy,


yes.......you probably have impeller fragments from this failure and possibly previous failures that are lodged in the PS/oil coolers.....

You should probably consider replacing the housing and other assoc parts too.....It's also possible that you have a leak somewhere in the suction side of the pump and is't sucking air. After you put a new pump in it try putting a clear vinyl hose from from the transom to the oil/PS coolers and look specifically for bubbles in the discharge from the pump. That'll tell you if you have a leak somewhere in the suction.

Also, you should get pretty good flow. Use a long enough hose to measure the amount of water coming from the pump to see if you might have an obstruction somewhere between the pump discharge to the oil/PS coolers......



Regards,


Rick

 

[kevlh21]

Re: OMC Cobra Water Pump Problems

that might be why my oil pressure drops so low after it warms up

 

[kevlh21]

Re: OMC Cobra Water Pump Problems

and what do you mean by PS?

 

[DBreskin]

Re: OMC Cobra Water Pump Problems

and what do you mean by PS?

PS = Power Steering cooler

 

[HT32BSX115]

Re: OMC Cobra Water Pump Problems

that might be why my oil pressure drops so low after it warms up

Um,


No. probably not. You may be getting low oil pressure due to high oil temp and thin oil but it's not really related as much to the plugged oil cooler as much as it would be related to the engine getting hot in general.

You need to find the reason for the obstruction and/or pump cavitating and destroying itself.

 

[kevlh21]

Re: OMC Cobra Water Pump Problems

this failed water pump explains alot of problems. I didnt think I had a power steering cooler...

 

[Gary H NC]

Re: OMC Cobra Water Pump Problems

Usually the PS cooler is on the starboard side of the engine just below the exhaust manifold.Pain to get to.

Take the hoses off and and back flush it from the front.
Also the thermostat can trap pieces of old impellers.

 

[havasuboatman]

Re: OMC Cobra Water Pump Problems

Blockage in the cooling system after the impeller would not have caused the new impeller to come apart. The only thing that would cause that is running the boat out of the water without a hose (it takes just seconds to start destroying the new impeller) or a blockage in drive that is keeping the water from making it to the impeller in the first place.

 

[kevlh21]

Re: OMC Cobra Water Pump Problems

where does the cooling water exit? After it cools the engine.

 

[kevlh21]

Re: OMC Cobra Water Pump Problems

I did run it for a few seconds out of water. I thought you were supposed to start the boat with the water on and turn the water off before you shut the boat down (to get the water out of the engine)

 

[havasuboatman]

Re: OMC Cobra Water Pump Problems

You never want to run the impeller dry. If you want to drain the block, use the block drains.
Just running a few seconds will get the impeller hot and will shorten its life span, but it wont cause it to disintergrate. More that a minute however, will.

 

[HT32BSX115]

Re: OMC Cobra Water Pump Problems

I thought you were supposed to start the boat with the water on and turn the water off before you shut the boat down (to get the water out of the engine)

No.

You want the water ON before starting the the engine and after shut down.

Don't run the pump "dry" for any reason at any time and it will last the longest.......

where does the cooling water exit? After it cools the engine.

Water goes into the oil/PS coolers, then to the block via the T-stat housing.

Some of the water is routed into the block (and circulated) when the T-stat opens.

some exits the block and is mixed with cold water that bypasses the block depending on how "open" the t-stat is at any given time......

All of the water then goes to the exhaust manifolds up though the risers, and is mixed with the exhaust gases and either out the Y-pipe (if installed) or out the thru-hull exhaust ports in the transom (if installed)


[we're talking raw water cooling here btw]

If you're "closed cooled" (full sys) then ALL the raw water will go to the heat exchanger and out through the risers..... Block and manifolds are cooled with AF......


Half system: Raw water exits the heat exchanger and goes thru the manifolds and risers.....

 

[kevlh21]

Re: OMC Cobra Water Pump Problems

that might have been the problem. I thought the water was on. someone turned it off (i couldnt see it) but it ran for at most a min before it was turned back on

 

[HT32BSX115]

Re: OMC Cobra Water Pump Problems

Looks like I edited my previous post while you posted! have a look.......


Sometimes 15 seconds is all it takes to destroy a rubber impeller in a dry stainless steel housing.......

 

[havasuboatman]

Re: OMC Cobra Water Pump Problems

that might have been the problem. I thought the water was on. someone turned it off (i couldnt see it) but it ran for at most a min before it was turned back on

You just figured out what happened, my friend.
Flush out the pieces of impeller, re assemble, REPLACE THE BURNED BELLOWS/COUPLER HOSES, and you should be fine.

 

[kevlh21]

Re: OMC Cobra Water Pump Problems

That explains why I need new rubber riser couplers. The heat blew a hole in one and burnt the other one pretty good. When i run with the hose connected no water comes through the prop where the exhaust exits. Is that normal?

 

[HT32BSX115]

Re: OMC Cobra Water Pump Problems

By the way, I still have my old PS cooler and hoses from when I removed the 460 from my boat......


If I remember correctly, the PS cooler has VERY small holes in it and would not pass impeller fragments at all...

The cooling water HAS to go through the PS (and oil) cooler before going to the T-stat housing.

If it were clogged enough, it could prevent any water from even getting through and could contribute to ruining the impeller.....

 

[havasuboatman]

Re: OMC Cobra Water Pump Problems

The cobra drives have a small vent in the pump housing that keeps them from dry starting when the boat is in the water. Having water in the housing is enough to keep them from melting and coming apart.
Those coolers do have small passages though and the impeller pieces MUST be flushed out of them or the engine will over heat in a hurry.

Yes, there is supposed to be water coming out of the propeller hub openeing.

 

[kevlh21]

Re: OMC Cobra Water Pump Problems

no water coming out of the propeller at all. When its hooked to the hose the boat takes FOREVER to warm up (the water is pretty chilly, I have a well) But I think that is because the hose is forcing water through the engine. What does this oil cooler/ps cooler look like?