I gave my 18 year old OX66 a vinegar flush

I had the lower unit off due to a recent complete water pump job.
I pulled the tstats and put the gaskets and covers back on. I filled a trash can with 8 gallons of straight vinegar. Hooked up a pump I bought and pumped straight vinegar into the flush attachment. As I suspected, 99.9% of it came out the water pump tube in the midsection. I recirculated it for maybe 15 minutes. Then I used my finger to plug up the water tube and after about 15 seconds I heard a gurgling sound coming from the areas of the tstats and I touched the tstat covers and they were very cold (the vinegar was in my garage all week) so I knew the vinegar was passing thru there now. Then much of the vinegar started exiting various areas of the mid section and I let it run like that for maybe 10 minutes then fresh water flushed for 15 minutes. Here are the pics. That trash can was clean before I started.

I've never used vinegar to flush my engine but I use it to rinse the boat to get the salt off. I use a pump up garden sprayer filled with vinegar and water to spray the boat every use. It cleans the salt off the window glass, fiberglass and SS rails. (My boat is on a mooring so a fresh water rinse is not going to happen).
On our trawler, my wife uses it in the galley and head sink drains as well as the shower drain and we pump some through the head every week.
Vinegar is great stuff!

many use Salt away. a good time to check all anodes inside and outside

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Had my lower unit off to replace the water pump and figured a good opportunity to do this vinegar rinse as Tim described. Typically replace the thermostats every other year but going forward after this, I should check every year. I was surprised how gunked with salt the t-stats were prior to the rinsing. After soaking in the vinegar they came out nice and clean. Below is pic of the bucket which was even dirtier with another rinse or two through.
Thanks for the tip!
Larry

Larry, one thing I noticed, and I am not sure if it's related....In prior years as far back as I can remember, after a cold start, the engine idled at 12-1300 rpms, then reached proper temp after about 60-90 seconds at which time it settled down to 800-850 rpms...The three times I have ran it so far after this flush, it doesn't reach operating temp and idle back for about 4 minutes (I timed it yesterday because the delay was so noticeable). Of course,the water temps are still in the low 50's so maybe that will change.... Let me know if you notice anything different when you get it back in the water....Other than taking longer to come up to temp, I haven't noticed anything different.

Thanks Tim. Will let you know if the same occurs. I will not be in the water till likely the second week(end) in May.
Thanks again - larry

My home has a tankless hot water heater and I do a vinegar flush similar to this on my unit once a year.
Never thought of doing it on the outboard!