Mercruiser EC Exhaust Manifold Overheat - Help Please

V

vasilios

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Hey, looking for some insight from the Gurus

I have a 2018 Cruiser yacht with twin Mercruiser Seacore 377 EC

Closed-loop cooling; the exhaust manifolds have coolant going through them

The elbows have fresh water running through them

I have a problem where, after four minutes at full throttle on plane, it goes into guardian mode

The error is port exhaust manifold coolant temp too high; it gets to about 214 degrees

I took off the port elbow, scraped out some rust from the ports, tested the flow, and it flows as it should

Reinstalled with a new gasket, the issue got a little better, but it still overheats after about 4 minutes at full throttle

The starboard side is staying at about 170 degrees

I also have a brand new seawater pump

I also swapped sensors side to side. I inspected the heat exchanger, and it's not clogged

I'm also kinda confused because, since it's all closed loop, the gasket between the exhaust manifold and the elbow has the block-off plates. So that sensor doesnt even get touched by coolant, and it's in the elbow

Any insight?

Thank you!
 
Lou C

Lou C

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Nov 10, 2002
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Don’t know your system but is there some kind of a control valve regulating flow to the elbow?
 
alldodge

alldodge

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First need serial number?
When was impeller last replaced?
Might be the poppet valve
 
tpenfield

tpenfield

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BTDT . . . I had (past tense) a Cruisers Yacht 338 with the Mercruiser 6.2L Seacore engines. . .{converted it to outboards} . . . I started getting exhaust overheats and it would go into guardian mode (3000 RPM limited). I tried to clean out the elbows using oxalic acid. It improved it somewhat but not entirely. I believe the remedy is to replace the elbows . . . IIRC they will run about $1500 for a pair, but the block-off gaskets are $200 each (total rip-off).

If you take the elbows off, maybe you can try to clean them out some more, but they may still overheat.

There is (should be) a poppet valve at the back of the engine which regulates the raw water flow to the elbows. I had considered taking out the valve from inside the valve body, but never got that far.

In the near term . . . perhaps you can run at less than full throttle and see where the exhaust temp stays within its limits.
 
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