"It depends... per thostorey&#
"It depends... per thostorey's post, which engine?
If the engine has an oil cooler or is fresh water cooled, its probably a good idea. Then again...not all salt water is the same. Where I live and boat, there is a fair amount of "eel grass" at times. Eel grass is a fine, long strand seaweed that...well... looks like grass. It has a proclivity for getting sucked up in engine cooling systems. Strainers are their own maintenance problem. Where I boat, they are checked daily before starting the engine. A full handfull of the stuff is not unknown. You also have to be very careful reinstalling the top of the strainer to make sure it seals, or you end up with an air leak and an overheated engine. Carrying a spare seal can be a day saver."