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Old 10-30-2015, 12:19 PM   #1
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Default Excessive Steam Mercruiser 5.7l raw water

Hello everyone......i need some advice or past experiences.

I have a Maxum 3100se 2006 had the Stb engine over heat at 3000 rpm a few weeks ago. So changed out the impeller and thermostat had the same issue. Bit the bullet and ordered new manifolds and risers, have just installed on the stb engine temps are all good now but when flushing with the ears once up to temp steam starts to come out of the prop exhaust and the water from the exhaust is a lot hotter than the port motor. also noticed it is not drawing all the water from the flushing ears compared to the port motor? any suggestions??

Thanks in advance for any advice.

Regards
Brad
Perth, Western Australia
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Old 10-30-2015, 03:59 PM   #2
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Welcome aboard.

What engine and drives do you have?

When the impeller was replaced was it in tack? Sometimes the vanes will break off causing a blockage in the system.

Additionally marine growth in the intake of the drive or inlet hose will cause a restriction.

What is the helm gauge reading?

I like to use a hand held IR temp sensor to take several measurements on the exhaust and engine as well as hoses to find what is in normal temp and what is not then this gives one the idea where to look.
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Old 10-31-2015, 12:20 AM   #3
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Thanks Mike

2 x 350 mag with Bravo 2 drives and the boat is dry stacked. the old impeller was intacted on removal.
Helm gauge is reading 71c (160f) at all rev ranges. Had a temp gun on the manifolds for both engines they are all around 86c to 94c (200f). top of the elbows can be touched while underway but do heat up when at idle but helm temp stays at 160f. I'm going to start working through the cooling system.....may have a restriction in the power steering oil cooler?

Thanks for the reply

Regards
Brad
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Old 10-31-2015, 02:58 AM   #4
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Brad the power steering cooler is the first thing in the cooling system and since the engine is right on the money I doubt an issue exists here. However the elbows on both engines are way to hot, 200 F is nearly boiling! What is the temp of the cooling hoses feeding the manifolds, what is the manifold temps?

Has the boat always been dry stacked? When did you first notice the hot temps?
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Old 10-31-2015, 09:44 AM   #5
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Mike, the manifolds on both motors are around 200f and the elbows are around 120f at 3000rpm. So all appears ok besides the steam on the stb engine. The stb engine elbows heat up when on the earmuffs while the port is fine.

I haven't tested any of the hoses as yet, but will do.

I have had the boat for 18months it has never been anti fouled so I presume it has always been racked.

It only started a few weeks ago when the overheat alarm went off during a run.
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Old 10-31-2015, 11:45 AM   #6
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Brad, sorry but the manifolds should not be that hot. I am assuming you have dry joint exhaust and the elbows have a cooling hose attached to the dry joint connection otherwise I cannot see how the elbows are cooler than the manifolds.

IMO the manifolds should not be hotter than 160 F. I am assuming you have a open completely raw water cooling system and not a closed system with a heat exchanger, correct?

Steam comes from boiling water, something is way to hot.
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Old 10-31-2015, 01:20 PM   #7
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Yes Mike, raw water cooling with dry joints. There is something definitely amiss with the cooling system. I think I'll work through all the cooling hoses and take some more readings.

Thanks for your advice to date

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Brad
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Old 11-03-2015, 08:36 PM   #8
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Hello all,

Found the issue, it appears the hose in the Bravo 2 leg was getting kinked and reducing the flow to the water pump. Will need to do further investigation why this has happened and maybe change out the hose. looks a reasonably big job as the leg will need to come off.

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Old 11-04-2015, 01:26 AM   #9
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Quote:
Originally Posted by Originalsin View Post
Hello all,

Found the issue, it appears the hose in the Bravo 2 leg was getting kinked and reducing the flow to the water pump. Will need to do further investigation why this has happened and maybe change out the hose. looks a reasonably big job as the leg will need to come off.

Regards
Brad

On the Bravos merc uses a plastic insert to secure the hose ends to the bell housing and inner transom, these are know to block for either marine growth or debrie. This will starve the raw water pump and the suction can collapse the hose.

Good time to replace the bellows.
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