My OMC Cobra is now a steamboat

Hello,

At the end of last season, a marine shop replaced gimbal bearing in our 1986ish OMC Cobra bored out 6 cylinder. It is connected to an OMC Cobra 5.7 liter outdrive. They couldn't reassemble the outdrive back on because the outdrive needed work itself. The upper unit needed new pinion gears, which they couldn't identify. I asked them to leave the outdrive off until I figured out the situation. They told me they would dump antifreeze in the upper hoses so it could winter the cold temperatures this last winter season. Meanwhile, in the winter, I figured out what pinion gears I needed, had a gentleman replace them along with a new water pump that is located on the backside of the upper unit. This spring we took all the necessary steps to replace the outdrive gasket, fill the outdrive with gear oil, stuck the muffs on, and started it up.

It was harder to start than usual of course (being the first time it ran this year). Was a little smokey for about 5 or so mins. About the time the thermostat should be opening up, steam started roaring from the exhaust exit (at the propeller) and the backside of the outdrive (where I think I usually see the coolant water exit). I'm hoping this isn't a sign of a bad headgasket or head. Am I missing something? We ran the motor for about 10-15 mins, but the steam is not letting up. We never noticed water pouring out where it normally pours out during a coolant system purge. Only steam...

Sounds like whoever did the impeller didn’t do it right or there is a problem with the water tube grommets inside the drive...
the Cobra impeller is very easy to replace....

We started looking into the impeller a day or so after I posted this. The impeller wasn't mounted well. The o-ring came out of the groove, and the shaft that slips into the rubber impeller doesn't reach the slot of the impeller blade itself, so it isn't turning it. Because water normally runs constantly through the exhaust manifold when the motor is running, it keeps the exhaust cooler as some level. When the impeller isn't working, the exhaust must be getting extremely hot. Once the thermostat finally opens, it's feeding coolant into the extremely hot exhaust and burning it up. Your reply makes me feel we are on the right track.

My problem right now is that the shaft for the impeller is only sticking out 3/4" past the metal plate that is part of the impeller assembly. So, it doesn't reach the slot inside the new impeller that I have. I need to gain more shaft somehow...

I made a reply below

Sounds to me like he assembled something wrong in the upper gear case! I always put my hands on the manifolds when running the motor it will tell you instantly if you can't hold your hand on them you have a water flow issue. With no water flow you can melt the exhaust flappers and the pick up tube seals between the upper and lower unit. The drive impeller unit on the cobras need a good seal and make sure the little hose off the impeller housing is clear and not blocked. You can also mess up seatting the pickup tube when joining the two drive halves. I also drilled a hole through the back plastic drive cover and ran the little hose from the impeller housing out of the hole as a tell tail it was pumping all the outboard have them! Good luck