OMC Cobra I/O Water Pump Problem

[shoreline]

I have a 1989 Stratos with an OMC Cobra engine. It is not circulating water so the engine is overheating. I replace the water pump (Impellar and all) and it will still not work. Can anyone help? Thank you

 

[olbuddyjack]

Re: OMC Cobra I/O Water Pump Problem

Did the old impellar break up when it failed? If so the pieces may be causing a restriction somewhere in the system.

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

The impellar did not break up, but it did shred somewhat. It was recommended to me to remove the hose from the thermostat and see if I am getting flow - if I am than replace the thermostat - if not than something is blocking the hose, perhaps a piece of the old implellar. Any thoughts? Thanks

 

[sea wolf]

Re: OMC Cobra I/O Water Pump Problem

Why did the impeller burn up in the 1st place? Just trying to get more info.

 

[seahorse5]

Re: OMC Cobra I/O Water Pump Problem

How about a model number so we know what motor you have and give you more than just a generic answer!

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

I am not sure the model number but it is a 1988 OMC Cobra 5.0 Liter. What we have done so far is replaced the impellar (no water flow), disconnected the hose to the thermostat to see if we had flow (no flow), then backwashed that same hose with the impellar, housing etc. off in case there was a blockage put the impellar back on (still no flow). Also checked the inlet screen on the lower unit and it's clear. Thanks for any help you can provide.

 

[olbuddyjack]

Re: OMC Cobra I/O Water Pump Problem

Hummm, how about the flow from the screen to the pump through the lower? You could have picked up muck or debris and plugged it there. The impellar drives off the back of the input shaft in the upper, is the end of the shaft turning? It should spin at engine speed anytime the crankshaft is turning. Keep diggin, the truth is out there...

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

The shaft is turning. I was thinking about removing the lower gearcase and checking to two seals (top and bottom) on the water tube as well as the housing. Thoughts.....?

 

[seahorse5]

Re: OMC Cobra I/O Water Pump Problem

Just make sure you did not install a KING COBRA water pump kit as the housing is different because the pump turns opposite rotation from the regular COBRA pump.<br /><br />Also note that if someone hammered on the pump shaft, because it's a press fit, it could move inward and not engage the impeller when everything is buttoned up.<br /><br />trace the water line from inside the boat at the transom and see if it goes to the oil cooler first and check there for any obstructions.<br /><br />It could be any number of things, and without seeing it we can only offer guesses and hints.<br /><br />Good luck.

 

[sea wolf]

Re: OMC Cobra I/O Water Pump Problem

Are u sure you're getting enough water pressure from the garden hose? With the triangular cover removed u should see water squirting fom the vent hole on the water pump cover when u turn the water on. Make sure that hole isn't plugged. I toasted my impeller the other day 'cause I didn't have the water turned up high enough. Also u can remove the pump cover & see if water is reaching the impeller when u turn on the hose. Look at the 2 ports & see if there's any water in them. If not, then either u don't have enough water pressure or there's a problem in the l/u.

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

Update: We have removed the drive from the transom and then the lower gearbox from the upper after draining the oil, etc. The seals, both upper and lower on the tube appeared to be OK, the lower was a little off but did not seem all that bad. The water housing is not warped nor cracked. We flushed out everything possible and there is no sign of any blockage. Tonight we will replace the upper and lower seals, re-attach the upper and lower gear case and attach it back to the transom - hook up the muffs and keep our fingers crossed! Is there anything we could be missing?

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

OK guys - here's the update. We have replaced the Impellar, the 2<br />lower seals on the lower gearcase and the thermostat on the engine. We<br />have also backwashed all hoses and cleaned the entire drive. The boat<br />runs well but it is still overheating with temps pushing 240+. When it<br />gets hot, we back it down to about 1300 rpm's and trim the prop up and<br />she cools down to 160 - 180. She does heat up fast depending on speed,<br />at idle the temp is between 180 and 200. On Saturday, the engine was<br />smoking when she hit 240+ so since then we back her down when the temp<br />hits 220 or so and wait for her to cool off. Any ideas?

 

[olbuddyjack]

Re: OMC Cobra I/O Water Pump Problem

How about the hose from the drive to the transom? Hook the ears up and tilt the drive with it running to see if it leaks near the port side of the bellows.

 

[Boatin Bob]

Re: OMC Cobra I/O Water Pump Problem

If you take the input hose off the thermostat how much water is coming out? I'm pretty sure my manual said if you hold the hose vertical you should get a stream 4 or 5 inches high. Do you have an oil cooler or power steering cooler in this line as well?

 

[seahorse5]

Re: OMC Cobra I/O Water Pump Problem

Have you checked to see if the risers and manifolds are plugged or restricting the outflow of water? That is one of the most common overheat problems on an older stern drive engine.

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

When checking the water inlet hose to see if it was binding we saw no evidence that it was however we noticed an obstruction in the upper<br />gearshift where the bellow connects. It was inside and lodged underneath the shifter. We noticed that it was very difficult to<br />shift. We removed it and it is a black/rubber and tan/very hard approximately 3"++round object. Seems like it was loged under the<br />shifter and in the canal. We have no idea whether we picked it up from the lake when the engine was up or if it came from somewhere. Any<br />thoughts?? It kind of makes sense, since that when the engine was up the temp went down to 160-180 and when we dropped the engine it went<br />over 200.

 

[Boatin Bob]

Re: OMC Cobra I/O Water Pump Problem

Could be an exhaust flapper? OMC Cooling Diagram go to this link and look at the diagram, item # 32

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

Looks like it could be, we were thinking the same thing.

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

OK - pulled out another piece of junk from the drive, just below the shifter. Found it after taking the boat out last night. It ran fine for the first 15 or so minutes and then the temp started to rise above 200 (prop trimmed all the way down and throittle about 3/4's down). Trimmed the prop up and backed the engine down to about 1300 RPM's, temp came down to 160. With the prop up, we increased speed and the temp still stayed at about 160. A few questions:<br />1. We are thinking that the junk we pulled out of the drive (combination of what looks like a seal, gasket and hardened brown stuff-2 sizeable pieces in all) are clogging the water flow with the prop down - any thoughts?<br />2. We have not yet diagnosed whther the hose from the drive to the thermostat is choking itself with the prop down. We will look at that tonight by pulling of the hose on the thermostat side and testing the flow with both the prop up and down - any thoughts.<br />3. No idea where the pieces we have pulled out came from - gonna need some help on this one....<br />Thanks for any responses.

 

[shoreline]

Re: OMC Cobra I/O Water Pump Problem

OK - Here's the update. We have replaced the upper and lower seals on the guide tube in the lower gearcase, we have replaced the impellar, we have replaced the flappers (those are the two pieces of junk we pulled out), replaced the gaskets on the risers after checking the risers and all for clogs, replaced and attached (because it was not attached to the drive) the exhaust bellow, replaced the thermostat, backwashed all hoses with the drive up and down, etc. making sure we had no blockages. Everything flushed fine. Still have the overheat problem. Yesterday we removed the thermostat and ran her again. After about 15 minutes at 3/4 throttle she heats up to about 2oo degrees. Pull the throttle back and she goes over 200. Lift the engine and maintain 1300 RPM's and she drops to 160--. Now if we flushed all the hoses and they are clear with the drive up and down, replaced the seals, checked the mainfold and risers, replaced the impellar, flaps, thermostat what else is left. The only thing that has not been checked is the large hose from the thermostat housing to the water pump. Can that have anything to do with it?