Mercury FourStroke 60HP overheating, difficult blockage

[tinyfish123]

Hi everyone, I'm writing in the hope that someone has a useful tip for me.

I have a 2021 Mercury FourStroke 60. It overheats on high RPM only. The issue started happening the day after sucking some sand (which at the time caused no issue).

I have checked the usual: tell-tale is quite strong, pump and impeller work well, thermostat works and I flushed in all ways. While the engine gets very hot, the water coming out from the tell tale is cold.

The issue seems to be that water doesn't flow through the engine block. Since I don't know the names of things I took pictures and tagged the parts. Per my observations (running without thermostat):

* Water flows up to thermostat (A) but it doesn't flow through (B). Putting water in B just overflows.
* I took the lower unit off. Flushing up from (4), which is the water hose going up from the pump, gets water to the tell tale. Blocking the tell-tale causes lots of pressure build up. Some water comes out of a tiny hole (3), but not much.
* I would expect water to come out from (1), is this wrong? Filling the engine with water though (B) results in no water flowing out.
* I also flushed up from (1) and (3), which results in water eventually coming down the exhaust (2). I did not manage to get water to come out through (B) when flushing from under.

I understand these engines do not have an additional popper valve that could get stuck, do they? Does anyone have any idea on how to deal with the issue given the information above?

Thanks so much!

 

[tinyfish123]

In case this is useful for anyone in the future... the issue and the solution were found.

Hole B goes into and through the "exhaust block". The water exists at the bottom of it through a 4x4mm square hole, that is, a tiny hole, smaller than the water intake holes (!),

The exhaust block can be opened by removing the 12 screws (2 of those are the thermostat ones). At the bottom, we found some tiny stones, one of the lodged in the water-exit hole.

These stones were sucked-in with some sand I guess. I think it sucks that the "world's most common outboard" can suck stones bigger than it's own water flow passages (they've had like 20 years to put a mesh in there somewhere to stop this). Unlike the rest of the cooling system, this part of the engine cannot really be back-flushed so any stone/objects that get in the exhaust block cannot go out the same way that they came in.

What's even more annoying, I spent a good hour convincing the Mercury dealer that a blockage really existed. Limited water flow meant most of the engine was cooled properly, and it was impossible to get it to overheat outside of the water, even by letting it run at 5000 rpm for minutes. This is because if the engine doesn't really need to push the boat, fuel injection will adapt accordingly, thus burning much less fuel and producing much less heat than in the water.

My take-aways:

* Most online content about "flush your engine"/"engine overheating solutions" is from people with little understanding of how debris can travel inside an engine and where it can cause issues.
* Learning about your engine is the best way to take care of it. Better than letting anyone else touch it. Some "professionals" won't go past checking whether there is water coming out of the tell-tale.

 

[Texasmark]

This reply was very thoughtful of you to take the time to help others that may encounter similar problems. Thanks