Re: overheating,3.8l omc with 3.0 l cobra stern drive
Running a Cobra in a bucket of water will not work. The impeller must be below the water line for it to actually move water. You can test with muffs to rule out a blockage, but you won't know the extent of your issues until you test with the boat in the water.
Like Kainon said, find the hose coming from either the transom or power steering cooler (if so equipped), and disconnect it from the 'stat housing. Connect a piece of clear hose to the end of it, and test by running the engine briefly while the boat is in the water. You should see a column of water coming out of the clear hose that shoots about 2"-4" inches straight up from the end of the hose. Also, check the water moving through the clear hose for signs of an air gap in the system (you will see bubbles).
If you do not have good flow from the end of the hose, check your PS cooler (or the hose itself) for debris that could be blocking it (you said you replaced the impeller, but you did not state if it was intact). You also may want to backflush the system while you have the hose extension connected.
If the line is clear (no debris), then the issue is in the outdrive. You'll want to check your impeller installation first (check that the screen didn't turn and the the impeller vanes are oriented correctly). If that checks out, you'll have to pull the outdrive and separate the upper and lower units so you can check the water tube (runs between the upper and lower units), and the water tube seals. Check the intake screen on the lower unit as well.
If you are still having issues after that, you may need to have your lower unit resealed (that's what I had to do). Keep us posted on your progress, please.
Good luck.
