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Old 06-26-2017, 02:41 AM   #1
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Default mercruiser 4.3 bravo 2's overheating

While Im trying to get a mechanic to come out I thought I would post the question here. I have a 2900 se with two mercruiser 4.3l with bravo 2 stern drives. It new to me, but the engines where started when I bought it and then the previous owner had the boat winterized. I moved the boat from new england to florida. Boat was floated and we tried to motor it to its new home. After 10 minutes engines got hot. they were shut off and boat was towed home. As im not a mechanic I will just tell you what ive found. Neither engine is moving raw water through them. When the blue drains were opened, hot antifreeze came out and then stopped. One of the engines has drains on the circulator pump. If they are opened they will continuously drain raw water, so I think the impeller is getting water. If the engine is run for a few minutes and shut down, the drains that stopped draining will release hot air when opened, and the two on the circulator pump still drains raw water. what would stop the raw water from going through the engine when it is coming into the circulator pump? could the winter of destroyed both engines impellers? Is there some kind of valve they close when they winterize the engines? Any other thoughts?
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Old 06-26-2017, 11:24 AM   #2
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There are two water pumps on each engine; a raw water pump that is belt driven and has an impeller that needs to be replaced every two years per mercruisers recommendations and a circulating pump on the front of the engine which typically lasts the life its bearing.

Common issues why water is not being moved through the engine are bad impeller, clogged intake on drive, clogged water hose on transom assembly next to bellows (know issue on Bravos), and clogged exhaust water jackets which is how the water leaves the engine to be discharged overboard.

Try removing the hose coming from the raw water pump to the t-stat housing and start the engine to see if water is coming out as this will tell if the pump is working or the clog is on that side of the system. Note the output hose of the raw water pump may go to a power steering cooler before the t-stat. The hose should be the second largest hose on the port side of the t-stat housing.
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Old 06-26-2017, 11:25 AM   #3
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Unless the factory installation was modified, there would be no seacock controlling the raw water intake. Raw water would be pulled in thru the lower unit, thru the transom assy and then to the raw water pump. To verify your setup is still factory, look to see where the intake hose on the raw water comes from. If it leads aft and then angles up to the transom assy then it's still OEM.

Most overheat issues with BII/small blocks are one of 3 things:
1) Restriction on the intake side of the raw water pump,
2) Bad impeller/scored housing on the RW pump
3) Restriction in the water path after the pump.

By far, most issues are related to #2. Running engine w/o proper water source can destroy an impeller in just a few seconds/a minute or two. Other cause can be from boating in sandy or silt filled waters.

More unusual would be #1 where there could be growth in the drive passges (I had a mussel growing in the intake hose or (known issue with Bravo's) transom assy has corroded around the connection where the hose from the drive passes into the transom assy.

Restriction on the output side, #3, could also be the culprit where the steering cooler or the t-stat housing has a blockage preventing water from flowing past that point.

Based upon what you have indicated so far, I'd lean towards verifying that the pump/impeller is in good condition. As it's a "new to you" boat, replacing the impellers would be a 1st season maintenance item anyway... They can (and will take a 'set') over time and even though they look "OK" will fail to pump properly. Same goes for the housing and thrust plate. If there is any scoring or grooves, replace the housing along with the impeller..

Also, if the impeller(s) are in bad shape and are missing any bits, be sure to track them down. Many times the impellers are replace and missing pieces are ignored and left in the system, potentially clogging up the power steering cooler, restricting the flow (leading to a hot condition).

Being formerly from CT, I am familiar with the seasonal process of winterizing and was amazed to see how many "pro's" potentially destroyed impellers/pumps by running too long without water/anti-freeze.

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Old 06-26-2017, 03:14 PM   #4
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Make sure the water intake check valves are open first. Easy to overlook.
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Old 06-26-2017, 04:18 PM   #5
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Quote:
Originally Posted by dannyrayz View Post
Make sure the water intake check valves are open first. Easy to overlook.
Do you mean seacocks? Check Valves are never used for engine raw water supply.

A factory setup does not use seacocks but instead gets raw water from a pickup built into the drive.
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Old 06-26-2017, 04:39 PM   #6
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Yeah, seacocks. Mine with 4.3's and closed cooling with Bravo 3's does have seacocks-factory.
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Old 06-26-2017, 04:51 PM   #7
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God morning everyone!
It sounds to me that the OP might have fresh water cooled engines! He had green antifreeze draining out, I would check both t stats and both HEs!
(edit) By fresh water cooling I meant closed cooling!!!
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Old 06-26-2017, 09:46 PM   #8
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Quote:
Originally Posted by donald View Post
God morning everyone!
It sounds to me that the OP might have fresh water cooled engines! He had green antifreeze draining out, I would check both t stats and both HEs!
(edit) By fresh water cooling I meant closed cooling!!!
Don
Don he said antifreeze but did not say it was green, however he said first start since after winterization so I assumed pink. He will need to clarify.
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Old 06-26-2017, 09:47 PM   #9
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Quote:
Originally Posted by dannyrayz View Post
Yeah, seacocks. Mine with 4.3's and closed cooling with Bravo 3's does have seacocks-factory.

May be a dealer installed but not factory.
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Old 06-27-2017, 03:28 AM   #10
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Mike, you are correct!
My big mistake!
Thanks for the correction!
Don
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Old 07-01-2017, 04:06 AM   #11
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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.
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Old 07-01-2017, 10:36 AM   #12
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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.
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Old 07-01-2017, 02:08 PM   #13
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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?
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Old 07-01-2017, 05:02 PM   #14
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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.

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Old 07-01-2017, 05:49 PM   #15
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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.
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