Hi, I have a 2003 Mercury 40 hp efi 4 stroke 3 cylinder that is overheating when at full throttle. Took to dealership and $1000 later they are unable to find problem and want $2000 more to pull power head with no guarantee of finding problem. Runs fine at idle but after about 1000 yards at full throttle solid tone alarm goes off and engine speed reduced to idle. After a few minutes at idle you can go again for short distance and then same thing happens. Engine feels hot. Good water pressure. Dealership put new thermostat and water pump in and checked all sensors. Problem still there. Motor was on pontoon and has seen really no mud or sand to plug up water channels. I had read a previous forum about a passage on a base plate under the power head that can get corroded and restrict water flow at full throttle. I brought motor home and will attack myself as I am not paying $2000 to pull power head with no guarantees to find problem. This motor only has 80 hours on it and has spent a lot of time sitting inside. Would manuals sold on this site be a good reference for power head removal? Any help or thoughts would be greatly appreciated.
Thank you.
Ben
Thank you.
Ben
