mercruiser 4.3 bravo 2's overheating

[bobgaudette]

Thank you everyone for the input. The engine is raw water cooled, it is not closed. The radiator fluid that came out for a short time was pink. I have two questions that maybe can be answered.

1. Is there anything a mechanic can do during the winterization of that engine that would stop the raw water from circulating past the engine mounted impeller?
2. as i mentioned in the post, the port side engine has two drains on the engine mounted impeller unit. when I open the drains, raw water continuously drains from them. Does that mean that the water intake from the stern drive is open and clear? Or is the water coming from somewhere else?

I cant see how it could be back flowing from the raw water out as I would think I would have water throughout the engine, and I dont have any water flow past the engine mounted impeller (will at least if I open any of the other 3-4 drains nothing comes out).

I would like to take the boat out on the 4th but cant get anyone to come out and look at it and wont run it until I can get water into it. Im gonna try and remove the hose of the t-stat but im sure nothing is going to come out.

You guys are the best. Thanks for your expertise.

[mmwjr]

1. If the engine is not warmed up when the mechanic went to run the antifreeze through the engine the t-stat will be closed and the antifreeze will not circulate through the engine. It will only go though the exhaust and out the back of the boat. Where did the antifreeze exit from that you saw?

2. If the boat is in the water then removing the raw water pump plug water will come out as you described so not totally blocked but may be partially blocked.

Yes run them shortly with the hose off at the t-stat to see if you have any water flow. You can also jam a hose into the t-stat and run the engine to see if it does not overheat.

If the mechanic ran the cooling system dry it will destroy the impeller. So remove the impeller for the winter to keep it from taking a set.

[bobgaudette]

Ok, so the back of the raw water pump has two hoses. One red and one black. The red one goes into the transom/stern drive so im assuming it the raw water intake. The black one goes to the back of the engine to a straight pipe with two small pipes off the top. If i remove the hose here and start the engine there is no water. So I think we have it narrowed down to the impeller on the engine or the intake is clogged/kinked. Mike said at the end of his post to remove the impeller during winterization. Is this a common practice? If so the pump may have no impeller at all. I dont have the expertise to remove the back of the pump housing to check. Am I correct in saying the bravo II stern drives do not have an impeller in the stern drive unit like the alphas do?

[jparsons121]

Bravo drives use a engine mounted raw water pump (no impeller in the drive(s).
Impeller issues are one of the primary causes of overheat issues as most do not service them as a maintenance item.. For the few bucks it costs for impellers, I changed them at least once per season.
When up North, I'd change it in the spring as part of the de-winterizing. In FL I do it 2x per year due to the high amount of silt/sand in the waters.

I remove the entire pump from the engine and service the unit on the aft deck..
Undo 2 hoses , 3 bolts and loosen the belt and it's out.

John

[mmwjr]

Ok so no water coming from the raw water pump. I believe I said some remove the impeller so it does not take a set, I don't do this but replace it every two years without issue.

Remove the belt.

Remove the entire pump by removing the two hoses then the two mounting bolts on the front of the engine to holds the pumps bracket.

Now easy to disassemble the pump. Note be sure to install the impeller with the blades curl in the correct direction, reference brave manual under Documents of this site. Additionally don't mix up the two hoses.