white streak on my outboard?

Salt water deposit caused by exhaust heat on the midsection housing?

 

Got your pic..

There's a weep hole in the cowling at the top of that streak.
Looks like a hard water line (calcium deposit) from a continuous drip from that weep hole.
You might have a small leak on a hose connection under the cowling.

 

is that the washout connector for a water hose?

 

then i would say it definitely has something to do with water leaking out and drying on the engine cover leaving a calcium deposit trail. try checking to see if all connections are tight and that the washer is still in the hose connector

 

any type of bathroom cleaner that wipes out soap scum and lime deposits.... basically all you have are mineral deposits and anything that will take of that should work. once cleaned i'd give it some wax.... should make cleaning easier next time around good luck

 

Plain vinegar. I keep some in a squirt bottle and spray the midsection to soak while I wash the rest of the boat. Household cleaners are much harder on the paint.