Re: OMC 5,8 overheating
You can also remove the impeller housing, and then hook up the muffs. Turn on the water and hold the muffs tight to the drive. You should see water coming out of the water outlet as you see it on the right side of the place where the impeller housing mounts. . If not, then there is a problem with the water screen, tube or seals that are in the lower unit. Next disconnect the raw water intake hose at the thermo housing and back flush this with a hose. The water should squirt out of the other passage (left side of the housing). If not you have a blockage somewhere between the transom mount and the thermo housing. Often old impeller blades from worn impellers lodge in the PS cooler or the thermo housing itself. Lastly make sure that the rubber o ring gasket for the impeller housing is in place correctly and it seals. You can check this when running the boat on the water hose. Leave the plastic cover that goes over the place where the impeller housing mounts and look at the housing when the engine is running. There should be no water leaking out around the housing. If so there can be air getting sucked in. Also there is a small hose on the impeller housing, when you disconnect this water should squirt out. It allows air to escape so the impeller can prime faster.
Ps, I have not had problems with Cobra impellers, as long as you get that rubber o ring to seal they usually work well. The one problem I have had with water flow, was because of marine growth. The old style Cobra lower unit has a water intake screen, just like a Johnson or Evinrude old style lower unit. If you leave your boat in the water all season you can get marine growth inside this screen. I had small barnacles growing in there (despite spraying the area with Trilux) and it is enough to cause the boat to run hot. I would up having to break out the screens and rod out the water passage with a stiff wire. BTW, Merc and Volvo drives do not have screens on the water intake holes, they have more holes but smaller. The Cobra has 4 larger holes on each side. I was going to fab up a removable screen mounted on the outside of the drive that could be removed easily to clean out the intakes but we don't have much crud in the water to clog them so I haven't done it yet.
