While getting ready to install my new starboard motor I decided to change oil and try new carb on port mtr while on muffs.Hose on full,start mtr,runs great,starts overheating,nothing coming out pipes.Pulled hose going to crossover and it was full of water.Didn't check stat but new and has 4 3/16ths holes in it. SW Pump is new and was giving 30 psi at full speed and 5-10 idleing. Nothing has changed on that side. Mtr is very rusty inside,, could flakes have plugged my oil cooler so quickly after weeks of perfect high pressure operation???I will backflush and check the stat and see but I'm stumped.Any ideas??

Did you have inlet and outlet hoses off the raw water pump? I reversed the 2 when rigging my engine (the bungs on pump are identical) and had the same exact problem,switched hoses,mystery solved! From what you said it didn't sound like you had touched them (although it wasn't 100% clear,you did mention a new pump). Good luck,Smitty

I've see Merc pumps suck so hard , they collapse the garden hose and cut off the water supply enough to cause over heating. Particularly in the hot sun with a soft hose and less than adequate water volume or pressure.

I'm Having The Same Problem. Had 2 New Long Blocks Installed. One Keeps Over Heating And Noticed Its Building Up Enough Presure In The Fresh Water Over Flow Bottle To Make The Anti Freeze Foam Up And Blow Out. I Stumped. All Pumps Are New And A Re Pumping Fine.

Collapsing garden hose from suction. Try it on the water.
Also could be internal collapse of 1 1/4" water hose between water inlet and pump. Hope you changed it with the new engine.
Gary

good info,thanks

We just lost two races and a motor from the hose that connects from the outdrive to the transom assembly. The first time we overheated and torched the motor, rebuilt the motor, thought we fixed what we considered a "fluke", just to get 2 1/2 lapse into the race in AC and the motor starts getting hot again, shut it down before we do any damage, let it cool, start it up, no water coming out the dumps. Get towed in, back on the trailer, the same hose got pushed up and kinked again.
Both times this happened after taking a hard hit off a wave in a corner.
I believe either the hose was replaced with the wrong one or installed improperly.
I'm not taking any more chances, converting to an offshore style pickup.