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I recently took over my father's 1997 Rage 15 with the OMC 115. It has had the raw water strainer since new. I believe this boat has a total of 40 to 50 hours on it. For the first 5 years it lived on the Port Saint Lucy inlet in Stuart, FL which I believe is brackish water depending on the tides. Since then it has had a fresh water life and has been used twice in the past 5 years. Now that I am trying to use it, it has an overheating problem. It will happily idle when using the garden hose flush kit, however it will give the overheat alarm on the hose adapter if RPMs increase to around 3,000 for approx 1 minute.

When in the water it will sound the overheat alarm after approximately 5 minutes, even if just idling at the dock.

The raw water strainer is clean. Water is flowing though it, both when using the garden hose flush kit and when in the water. I back flushed the water intake port and it is clear. I cannot check the condition of the raw water pressure relief valve in the impeller housing because the relief plug is stuck in place.

I purchased the factory service manual and an infrared thermometer to trouble shoot the overheating and determined today that the cylinder heads are operating at different temperatures. On the garden hose flush kit, the starboard head runs approximately 10 to 20 degrees hotter than the port head. Today, after idling approx 10 minutes, the port was 168 and starboard was 188. After idling approx 15 minutes, the port was 178 and starboard was 190. I then increased the RPMs to 3,000 and after 1 minute the port was 185 and starboard 200, at which time the overheat alarm sounded.

Not sure if it's relevant, but the engine also emits an occasional knock (approx every 10 seconds), which I guess may just be an occasional miss fire? I attribute that to the gas being a mix of preserved 2 year old stuff mixed with some fresh.

At this point i believe my next step is to pull the motor and check/clean/replace the thermostat on the starboard head... Anything easier I should try first?? The owner's manual says that after a repeated overheats to have the cylinder head and exhaust cover screws torqued... But I haven't found a specific sequence for doing that in the service manual.

Any help or suggestions are appreciated!

Thanks,
-Keith

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Update:

Just noticed I didn't update this thread... Problem was found to be a clogged cooling passage in the bottom of the motor. Mechanic cleared the blockage and the boat has been happy ever since. :)

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do you know where this cooling passage was? I need to check mine as well.

Thanks.

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I believe the passage was in the adapter plate, possibly where the U shaped rubber hose connects on the side. Unfortunately I didn't get a visual of the location.

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Okay...I am sure I know where that is. I will check that out this weekend when I am elbow deep in the motor...

Thanks a million.