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OK bear with me. Not a mechanic. 2016 R3 300hp overheated today on the lake. Took it home and checked impeller. Brand new as suspected. Greased, replaced. Put a hose on the flush line. Ran great stayed around 160 degrees. Water coming out where it should be and the water vents so I'm thinking no blockage. Must be raw water issue. Tried muffs (to simulate lake) and no water coming out-temp rose quickly.
Does the raw water pump sound like the issue? Do these things fail? Can I take cover off the pump and see if the impeller is turning on a quick crank? Belt is fine and is turning. Thanks for the help.

Sounds like your pump/impeller are fine if it runs ok on the flush. I guess there could be some sort of blockage with the pickup from the drive, but before you go too deep into that, make sure all of the hose connections on the pump are tight AND the cap on the flush hose is also tight. If the flush hose cap is not tight, it will suck air and cause problems.

Thanks for the reply. It's tight. One of the first things I checked. The impeller is turning fine as well. Does this boat have a raw water strainer? The trim was just serviced. I don't know what that would have to do with anything though.

How could I find the correct impeller for my boat? It might be the wrong one

Should be on the engine beauty cover - sticker with various part #'s.

No strainer, another place to check is the power steering cooler - raw water runs through it - just disconnect the hoses and check for debris.

Which hose to the pump is the intake from the vents? The larger or the small?

Pretty sure the larger one, follow it and it should run back towards the rear - small one would go up and connect at the thermostat housing.

Thanks for the advice!

Is it direct lake water cooled or does it have heat exchanger?

Does the boat stay in the water? Salt water? Could there be marine growth clogging things up.

Heat exchanger and the boat is stored in garage and fresh water only.

Whole system seems to be fine except no water coming in through the lower unit. And this is only happening after the dealer replaced the trim mechanism. Baffled. Worked fine when it was put away.

Bean wrote: Sat May 13, 2023 3:32 am Whole system seems to be fine except no water coming in through the lower unit. And this is only happening after the dealer replaced the trim mechanism. Baffled. Worked fine when it was put away.

Answer may be in the last sentence.

Seems like you have checked the obvious, if it was fine before the trim system work was done then I would start looking there. When you say trim mechanism, I am guessing the trim pump / housing which is located in the transom assembly (outside the boat) on your model - mine is the same way. Everything around the trim pump - hoses etc - is jamb tight. There is also a hose running from the bell hosing and through the transom assembly, this is your water pickup hose and runs through the transom assembly to the raw water pump. My bet at this point is something with that hose was disturbed during the trim system work.

What was done with the trim system?

Replace trim pump and cylinders