CONTINUOUSWAVE

Q1: will using a vinegar flush of the cooling system on my Yamaha Saltwater series 200 on my [1994] Outrage to clear any scale be likely to cause smaller ports in the head to clog and block the flow of cooling water ?

Q2: how small are the cooling ports on a [1994] Yamaha 200-HP Saltwater Series engine?

The engine has about 615 hours running time, has not been rebuilt, has been operated primarily in Florida on the ocean, and I am now using it exclusively in freshwater.

My motivation for using a vinegar flush of the cooling system is because the engine is overheating a maximum engine speed.

Replace the thermostat first.

Use a product designed for cleaning the cooling system like SALT-AWAY.

https://www.wholesalemarine.com/salt-away-salt-remover-kit/

Vinegar (which is acetic acid diluted in water) is often used as a weak acid to remove mineral deposits from cookware and coffee pots where fresh water has been heated, particularly when the fresh water is ground water that contains a small concentration of minerals, as typical of ground water from a well.

Whether vinegar (very dilute acetic acid) is the best agent to remove deposits in an outboard engine cooling system that have built up from having used the outboard engine in saltwater is unknown to me.

The pH of saltwater is said to average 8.1, which means that saltwater is a weak alkaline.

Cf.: https://sfyl.ifas.ufl.edu/media/sfylifa ... and-pH.pdf

The pH of 100-percent acetic acid is in the range of 2 to 3, which is a rather strong acid. But the usual vinegar sold as a food product is diluted in water so the concentration of acetic acid is only about 4 to 7-percent.

Cf/: https://www.vdh.virginia.gov/environmen ... tic%20acid.

Thanks for your input, appreciated. I did some more research and found two brands of marine descaling agents apparently safe for use in outboard cooling systems. These are Rydlyme and Hammerhead, both available on Amazon. I also found that vinegar is an acceptable alternate in lieu of those brands, at least on the blog I visited. I will change out the thermostats first, inspect the condition of the water jacket as much as I can from the thermostat removal, and then perform the flush if the matter isn't resolved by replacing the thermostats.