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Old 12-22-2013, 10:58 AM   #1
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Default Overheating sometimes

I have a maxum 2400scr from 97 with a mercruiser 5.7 freshwater cooling, using alpha one gen2 as water suppliant for the heatexchanger, I bought it in the beginning of this year,
After a few weeks i got tired of the clapping sound from the outdrive and drove the boat to a workshop,
they lifted the boat up and mounted off the outdrive, nothing was wrong except that some plastic shims were missing and that made the outdrive clapping against the gimbal.
When I picked the boat up and drove away it didn't take more then 5 min before it over heated.
Turned the engine off and tried to se if anything was wrong and I couldn't find anything,
Started her up again and continued my journey home, the trip were 1,5h long and i hade a speed at 7kn and no owed heating problem, for the moment I just thought it was air in the system after they had it off,
Then later this summer on my vacation it overheated a few more times, and every time it was just temporary, just like it peaked at overheating and went back to normal temp.
I found out that it leaked freshwater coolant and fixed the leakage and after that I blown my headgasket.
My question now is, how come that the engine was overheating in just a few seconds up to max 30 seconds?
If it was low on coolant shouldn't it overheat continuously and not just a few times,
Total this summer I used the boat for about 40h and almost never went over 7kn.
Could it just be a coincident that it overheated after it was at the workshop?
Now I have torn apart the engine and when I drained the engine on coolant there were no debris in the coolant, just a clear blue liquid as it should be.
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Old 12-22-2013, 11:42 AM   #2
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Fippe welcome aboard.

From what you have described I bet the engine was always running hot. With a closed cooling system that is low on coolant it is common that air collects around the higher part of the system which is where the temp sensor is located. This sensor is signed to measure coolant and not air therefore will not reflect true engine temp. This lead to the head gasket failure.

For the future get a hand held IR temp gun and measure engine temps; t-stat housing, manifolds, risers, ... I do this at the beginning, mid and end of every season.


BTY: What closed cooling system is on the engine? Not all are designed to work with the Alpha as it's raw water pump doesn't have the same flow rate as inboard pumps (Bravo). Verfiy vendor manual says it will work with the Alpha.
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Old 12-22-2013, 01:24 PM   #3
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Quote:
Originally Posted by mmwjr View Post
Fippe welcome aboard.

From what you have described I bet the engine was always running hot. With a closed cooling system that is low on coolant it is common that air collects around the higher part of the system which is where the temp sensor is located. This sensor is signed to measure coolant and not air therefore will not reflect true engine temp. This lead to the head gasket failure.

For the future get a hand held IR temp gun and measure engine temps; t-stat housing, manifolds, risers, ... I do this at the beginning, mid and end of every season.


BTY: What closed cooling system is on the engine? Not all are designed to work with the Alpha as it's raw water pump doesn't have the same flow rate as inboard pumps (Bravo). Verfiy vendor manual says it will work with the Alpha.

Ok, but when I have the right level of coolant the temp gauge show the same temperature as earlier.
If I have a permanent cooling problem that should have shown the last trip that was around 25nm in 21kn when the coolant was topped up.
The freshwater system is from orca marine and is a half system.
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Old 12-22-2013, 01:54 PM   #4
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Ok, you did not mention this in the origional post.

So right now the engine is apart to replace had gasket, correct?
Who installed the orca sytem? Did it ever run correct? What is the part number?

When the outdrive was reinstalled did they use a new gasket and o-ring, may be loosing pressure if not?
Does it only overheat at fast or slow speeds?
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Old 12-22-2013, 03:04 PM   #5
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i'd pull the end caps off my heat exchanger and look for seaweed, or blockage.

It sounds like the engine water pump is working, and the T-stat is opening.

Its easy to check by hand, if you can have someone else drive the boat:

just open the engine hatch, and feel the raw water line in for how cool it is, the raw water line out for how hot it is.

then the heat exchanger engine in and out.

hot, cold, hot cold......
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Old 12-22-2013, 04:57 PM   #6
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Sorry for that, thought I got that information in the original post.

That's correct the engine is apart right now, I don't have the part number for the cooling system available at the moment,
I took it apart now when it's off and ordered new gaskets and end caps and there where no debris inside it, every tube was clean.

I think they used new gasket when they re-installed the outdrive,
It has only overheated at slow speed, but 95% of the usage has been in slow speed.
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Old 12-22-2013, 05:05 PM   #7
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Forgot too mention that I don't know when the freshwater system was mounted,
The boat is imported from the states to Poland and from there to Sweden.
But when I look at the intake and heads it looks quite good inside. A thin layer of brown rust color.
Like when a break disk on a car stands in rain for a couple of days and ain't used.
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Old 12-22-2013, 05:39 PM   #8
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Is the thin rust only in the water passages? Not around the valves? Have the heads inspected for cracks before reassemble.

Inspect the exhaust manifolds and risers as well for rust. These are also heat exchanges, exhaust in center covered by water jacket.

Do you know when the raw water pump impeller was last changed? Should be every two years. May want to replace it. It's located in the outdrive md section.

I still strongly recommend getting a hand held IR temp sensor to check engine temps once rebuilt. I don't trust boat gauges. Once you know the temps with the IR sensor you can correlate that to the gauge.

At this point it's hard to troubleshoot with the heads off. Can only inspect for issues then test once running again.
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Old 12-22-2013, 06:12 PM   #9
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The rust layer is only in the passage.
The heads has been on renovation, they cleaned them up and changed two intake valves.
They also fixed the rest of the valves so they are not leaking.
The impeller in the outdrive I don't know. Therefor I have changed it now.
The manifolds and. Risers were the first ting I changed after buying the boat. The seller couldn't tell when they were last changed.
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Old 12-22-2013, 09:20 PM   #10
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Good you're on the right track.

Question: does the system have a coolant recovery bottle (overflow bottle)? Just like your car does.

If not every time you run the engine some coolant will be lost into the bildge as it expands with heat. Eventually the system will get low.

My wifes car used overheat once and a while until the head gasket went and the heads warped. After rebuilding the heads the problem went away.
Just wondering is loss of coolant resulted in failed gaskets. these can act flacky at first until they final give out resulting in water in the cylinders and oil, ...

At this point I recommend putting the engine back together and replace the impreller. Then see how it runs checking the temps as I have said before with the IR gun, ~$50 US

Good luck and keep us posted on progress
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