2019 Mercury 60/40 efi 4 stroke overheating

[alaskaboaterjt]

Looking everywhere and trying to find an answer

My motor has 150 hours on it and has ran flawlessly.

This summer I've been able to put about 10 hours on it before it developed a massive overheating issue. Can make it about a mile or 2 before the motor shuts off and the alarm kicks on. By the spark plugs it feels warm but fine. The further you move back towards the front of the motor the hotter it gets. Touching by the starter on the block is basically too hot to hold your fingers on. Lots of steam coming from exhaust.

Rebuilt water pump, no change
Took the thermostat and cover off, seems to be a pretty good stream of water coming out
All rubber lines clear
Pees strong. But the stream is always cold even when the motor is burning up
Tried running it without the stat, still overheats
Essentially nothing I've done works and it looks like. There is flow - how is it not cooling?

Last thing I would mention is the only place there was blockage was in the jacket - the little plastic screen that is before anybody the hoses exiting the jacket and that was pretty gummed up with jet pump grease.

Only thing so can think is somehow the exhaust/water and crossing over and that's why there is so much steam or because I found grease in that one place there could be more of it in the deeper channels of the motor.

Any help would be appreciated

 

[StuarBell]

My 60 HP Mercury Power Stroke has the same problem. Cleaned t-stat, checked flow from pee tube (fine), plew air thru t-stat openings - seemed clear.

How do I clean the water jacket?

There was shells in the t-stat that I cleaned. Now running without a t-stat -- new one on order.

 

[tdonoughue]

If there were shells in the thermostat, there are shells in the water jacket and probably everywhere. Other than breaking down the whole engine, might try a good flush. I don't think air is going to do it. Probably need to fashion something so you can force water into the block and then drain on the other side.

 

[Neutron]

New thermostat, for sure. While its out flush out both ways with good water pressure. Remove lower leg and backflush. Disassemble the raw water pump and inspect everything for debris.
Unfortunately you sucked up and restricted flow somewhere and need to clean it thoroughly. Hopefully its not clogged up the coolant passages in the head/cylinder.