Yamaha S150 1999 Saltwater series Flush question

[Soundear]

When I call Yamaha about the correct method for flushing this motor,, they tell me not to run the engine while using the flush attachment from my garden hose. Some Local mechanics are telling me to run the motor for 5 minutes. Does anybody know the cooling flow direction from the water inlet connector through this motor? I think yamaha does not want you to run the motor because the flush inlet is after the water pump intake so starting i the motor will run the impeller dry. If this is the case, how can i be assured the Thermostats are opening allowing the fresh water w/ Salt Away to cleanse the water passages at the heads if the water never gets hot enough to open the Thermostats?

[DennisG01]

Generally speaking, yes, the recommendation from Yamaha is to NOT run engine when using the cowl-mounted flush attachment as you may not get enough water down to the impeller to prevent it from melting. However, I remember reading on here somewhere that someone dropped the lower unit and observed that there was enough water dropping down to keep the impeller safe. Search around and you might be able to find that thread - and certainly more threads discussing this.

That said, why not just just use a flush attachment (muffs/rabbit ears)?

[99yam40]

hook up the muffs and the flush and then run the motor

[Sheff 69]

While recently rebuilding my 90 hp 2 stroke, I noticed that if you use the "cowl mounted" flush attachment and run the motor, the water flow is counter to the flow of the impeller.
If you let the engine RPMs get too high, and the water pressure in the hose is not good, I would assume you could starve the impeller. I'm assuming the flow in my 90 is typical of Yamaha's normal practice.

[Soundear]

Just needed to confirm my suspicions! Thanks to you both for your advice!