Cobra Overheating w/new water pump kit

[MercHelp]

I have a 1989 OMC Cobra 4.3l Engine. I have replaced the Water Pump along with the Impeller housing. Good water flow with the muffs/hose on but I put the boat in the water there is not water flow at all. I have taken off the Water Pump and flushed water back down the to the pick-up screens on the lower unit and water is flowing well. Hooked the hose and muffs back on and turn water on with very low pressure and there seems to be good water flow going back up to the water pump. I am out of ideas to try, does anyone have an solution to this issue?

Thanks!

 

[Levinz11]

Re: Cobra Overheating w/new water pump kit

So the hose going to the thermostat housing has good pressure on the muffs? But no pressure when in the water?

 

[MRS]

Re: Cobra Overheating w/new water pump kit

Check the thermostat?

 

[MercHelp]

Re: Cobra Overheating w/new water pump kit

yes,

Good water flow on muffs from the intake hose, no water flow when boat in water

 

[bruceb58]

Re: Cobra Overheating w/new water pump kit

Pull the hose going to the thermostat while in the water and start the engine for a few seconds and see what your water flow is.

Might be worthwhile putting a clear section of hose between the thermostat and the hose going back to your drive to see if the pump has an air leak that is causing an issue.

 

[Hoosmatroos]

Re: Cobra Overheating w/new water pump kit

Does the cobra have a small piece to secure the impeller to the drive shaft?

 

[MercHelp]

Re: Cobra Overheating w/new water pump kit

There is no water coming out of the intake hose that connects to the Thermostat housing when the boat is in the water.
I have taken the little tube off of the Impeller housing while to boat was in the water and there was water coming from that
when the boat was running.

 

[Gangly]

Re: Cobra Overheating w/new water pump kit

Very good suggestions above. I would first check to make sure that the themostat isnt stuck.

Also, the reason your are getting pressure with the hose attached could simply be because of the pressure provided by the water hose iteself. Check to make sure the impeller shaft hasnt stripped out the inside of the impeller or that the impeller blades are still attached to the impeller. If the inside of the impeller is stripped or the blades are missing, you would have good water pressure with the muffs attached but none without.

Good luck and let us know what you find out.

 

[MercHelp]

Re: Cobra Overheating w/new water pump kit

Water is not even getting to thermostat, when on the muffs it cools and runs great @140 so the thermostat is working OK. When in the water the impeller housing gets hot since water pump is not drawing water.

 

[bruceb58]

Re: Cobra Overheating w/new water pump kit

Did you replace the o-ring when you replaced the housing? How was the pump working before you changed it?

When you test it in the water, the boat is entirely submerged in the water right? Not just sitting on the trailer with just the drive pickup submerged.

 

[MercHelp]

Re: Cobra Overheating w/new water pump kit

Yes, the boat is completely in the water and I did replace both the housing and O-ring as well as the liner, plate w/ new gasket when I replaced the Impeller.

 

[bruceb58]

Re: Cobra Overheating w/new water pump kit

Have you had the lower half of the drive removed for any reason? There is a water pickup tube in there with water seals that could leak air but not likely the problem if the drive is completely submerged.

Was the engine run without water going to your new impeller, even for a few seconds?

 

[MercHelp]

Re: Cobra Overheating w/new water pump kit

Yes, but I have checked the Impeller and it is still OK. I hooked the muffs back up and she cools right down.

Also I have not had the lower unit off

 

[bruceb58]

Re: Cobra Overheating w/new water pump kit

Somehow you may have an air leak in your pump so you are losing prime. Actually, that's a little odd since when you are sitting in the water, your pump should be submerged so even if there was a leak, you should still prime up fine. Only when you start moving and the pump rises above the water line will you have an issue with that.

Pull off your impeller housing and snap a picture and post it. maybe you are missing something that someone else might see.

You aren't the first person to have this issue. Do a search to see what other people have found. Are you using an OEM impeller kit? If not, you might try getting one. If you are using a Sierra kit, all bets are off on your success.

 

[MercHelp]

Re: Cobra Overheating w/new water pump kit

Well one thing I have noticed while the boat is on the muffs, there is water leaking from around the impeller housing. I have tighten down the bolts but I do not want to make it to tight as not to crack the housing but still see the water collecting around the housing

 

[bruceb58]

Re: Cobra Overheating w/new water pump kit

Well one thing I have noticed while the boat is on the muffs, there is water leaking from around the impeller housing. I have tighten down the bolts but I do not want to make it to tight as not to crack the housing but still see the water collecting around the housing

Well, that's a problem. It should be water tight. What housing did you buy?

Have you had an issue before you changed these parts?

Torque specs for the impeller housing is 108-132 in lbs.

 

[MercHelp]

Re: Cobra Overheating w/new water pump kit

Well here's the story. When I bought this boat the previous owner had placed an electric (12Volt) water pump between the outdrive and engine so I knew there was issues with the pump in the outdrive. When I got into the water pump the Impeller had no blades left. That's when I got the new water pump kit from Wholesale Marine. I will have to go back and check the maker of the kit.

 

[bruceb58]

Re: Cobra Overheating w/new water pump kit

I would also check all the hoses along the entire path for kinks. When you are on muffs, maybe you can overcome any restrictions. Don't forget the small hose that connects the upper gear housing to the transom housing.

 

[MercHelp]

Re: Cobra Overheating w/new water pump kit

When hooked up to the muffs I have disconnected that hose and do see water coming out of the water pump housing. What does that hose do/go, is this the one that you say goes to the transom housing?

Thanks!

 

[Levinz11]

Re: Cobra Overheating w/new water pump kit

Just curious if the impeller shaft is even turning. Turn the motor over when you take the housing off next.