1989 OMC 4.3L Cobra Overheating

I need some guidance before I bust out another thousand (B.O.A.T.) on my boat.

My boat is overheating.
I have a new impeller and I checked it today when we got back and it is perfect condition.

That leaves me with 3 options.
1. Thermostat is bad (I HOPE!)
2. Water pump on engine is bad but generally when this happens on these types of engines, water will leak from the pump and that is not happening. (Correct???)
3. The pump for the impeller is bad. (or am I wrong on this?)

Being new to sterndrives I am trying to get some guindance before I start throwing money at this thing. I don't want to take it to a mechanic because they will tell me I need to replace everything under the sun. I do have an OMC Sterndrive manual. And I am fairly mechanical so I am thinking I should be able to fix this myself.

Any help would be greatly appreciated.

Thanks,
Ron

Re: 1989 OMC 4.3L Cobra Overheating

If it only overheats when on plane the seal between your lower and upper unit going to the water pickup could be bad. you might try a piece of clear hose sectioned in on the hose from the water pump to the motor. Drive boat and watch the water flow.

James

Re: 1989 OMC 4.3L Cobra Overheating

Well I got the boat home and took the impeller apart and it looked good. I hooked up the muffs and started the boat and watched the temp guage. The temp never got above 160 to 170. When it got that hot, the temp would drop back down. I ran the engine for about 30 minutes with the muffs and it never got hot so now I am at a loss. The water coming out of the stern was hot so I know it was circulating through the engine.

I do know that my buddy started the boat with out the stern in the water and no muffs. Sure pissed me off when he did that. He doesn't know boats. Needless to say he won't be doing that again.
Is it possible that I had air trapped in the system causing it to overheat? And now that I have hooked up the muffs and ran the engine for about thirty minutes is it possible the issue has been resolved?

On the water, the temp started rising while just cruising at no wake speed through the marina. The temp was about 200. When I started to throttle up, the temp started to rise and by throttle up I mean just passed no wake speed. Before today the temp would immediately start to drop back down to 160 or so.

Re: 1989 OMC 4.3L Cobra Overheating

that is a small possibility. if everything appears good now, take boat out again, see if it still overheats. any odd noises noticed?

water leaking from water pump on motor is def a sign of failure, but it doesn't always happen. pump can fail and not leak.

Re: 1989 OMC 4.3L Cobra Overheating

I have not heard any strange noises. I plan on taking it out this evening when I get home to see if she does it again. I sure as hell hope not.

Wouldn't hurt to replace the thermostat either I'm sure. It might have stuck closed or something. Thermostats are cheap and a good place to start.

I thought I had a water leak when I was working on it yesterday. I had the muffs on and water going and when the hot water was coming out of the stern it was catching the drain plug hole and running into the boat. Scared me for a minute.

Re: 1989 OMC 4.3L Cobra Overheating

change your thermostat. if you can get it out of the housing let me know im stuck there