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Ted G.
Ted G., Rigger, Diagnostician
Category: Boat
Satisfied Customers: 6159
Experience:  40 years boating, Safe boating instruct., Offshore Race promoter, Failure Analysis, Expert Witness
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I have a 2017 Mercury 60 4 stroke. On my third trip out,

Customer Question

I have a 2017 Mercury 60 4 stroke. On my third trip out, after running for a couple of hours, the motor would not let me get above apx 2500 RPM without starting to seriously miss. Then my over heat alarm began to go off. Unfortunately I was 4 miles down river with no one around. Over the next 3 hours I had to keep the motor around 1500 RPM to return to the dock. Every time the overheat alarm went off, I would throttle back to neutral. After a minute I'd go back to 1500 RPM to continue up river. After getting home I put the muffs on and the motor still cranked and idled as always. I'm afraid I may have gotten sand into the thermostat which is leading to the overheating. It still has a strong stream of water coming out as it always has. I have it in the shop for diagnosis but while waiting over the next t couple of weeks to find out the issue, I'm super concerned I may have done some significant damage by returning to the dock under those conditions. My question is, considering Mercury's Guardian System and keeping it at that low of an RPM,
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Is there anything else important you think the Marine Mechanic should know?
Customer: Sorry, didn't finish. Being that I kept it at that low of an RPM, and would drop off each time the alarm went off, what's the chances of significant damage to this new motor?
Submitted: 3 months ago.
Category: Boat
Expert:  Ted G. replied 3 months ago.

I would think you should be okay. the main thing is you had good water flow from the tell tale. That means the engine was likely getting it too. And even if some flow was restricted, the lower rpms would keep it cooler. Also a good idle would not be possible if you burnt up a piston for instance. Hopefully it will turn out to be a faulty sensor and all will be good.

Customer: replied 3 months ago.
Thank you. That reduces the anxiety over this. Lol
Customer: replied 3 months ago.
I will add that the motor was definitely hotter than normal. Also, the water coming out was really warm. Not scalding, but wouldn't want to keep my hand there for a couple of minutes. Does that change your opinion any?
Expert:  Ted G. replied 3 months ago.

No, I am focusing more on the fact that it idled well after the event. And if it wasn't steaming out the telltale that is a pretty good sign. It takes around 300 degrees at the cooling jacket before cylinder or head damage will usually occur so warm water is still your friend.

Customer: replied 3 months ago.
I've got to quit asking questions for my sanity. Lol. At one point, I did get a spurt of steam hat lasted maybe a second. It didn't do it after that. As I said, it was really quick and was early on on the trip back.
Expert:  Ted G. replied 3 months ago.

From everything you related I would not suspect any serious damage. The protection system is there for a reason and it seems to have worked.

Customer: replied 3 months ago.
Great. I'm leaving it at that then. Thanks for the info.
Expert:  Ted G. replied 3 months ago.

You're welcome, thanks for using our service.