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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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