hi guys i need help , i have 5.7L mercruiser 260HP engine and it overheats. I have cleaned the outdrive and made sure there was nothing blocking the water intake. I have also replaced the thermostat making sure it was not stuck. Now it over heats and i dont know what to do . Is there anyway i can flush the cooling system. The impeller is also good . How do you flush the cooling system also the engine is a 1991 with alpha outdrive. All help will be appreciated thank you ,

Welcome to OSO.
First this thread is not in the right place. You should have it placed in a section that it more pertains to.
Have you checked the oil cooler? the water path runs from the drive to the oil cooler then to the engine. If impeller pieces, trash etc get clogged in the oil cooler the engine will not get much flow resulting in the very symptom you have described.

Did you replace the impeller in the outdrive?

yup guarenteed thats the problem

yes i did but it was 2 years ago but on idle the water flow is good so i know the impeller is doing its job

well the problem is that i dont know how the oil cooler looks like or what hoses go to it . is there any link or picture you can send to me to show me . Thanks

also since my engine and outdrive is alpha 1 i dont think its has a second raw water pump inside the engine besides the outdrive impeller so impeller pieces can not be stuck in there as well as my engine is sea water cooled inside . so there is no heat ex changer or what the case might be for antifreeze cooling aka fresh water cooling

yes i have 2 years ago tho but i checked and good water flow is coming in from the outdrive so i know its not that

A two year old impeller can go on you. Just because it is working at idle doesn't meant you do not have a cracked or busted blade. As normal maintenance after 2 years I would change it just to rule it out.

right it might have enough left to spit some water in there. Check it and change it, and try again. Other than that, you would have a blockage somewhere.