Descaling Yanmar 2cylinder raw water system

[Avi]

I need to descale my 1979 yanmar 2qm15 . I have a raw water cooling system. How exactly I do it? Can anyone explain to me the process?
Can I use a mix of vinegar or it has to be a specialty marine descaler solution.
Thanks

 

[S/V Honu]

I used muriatic acid on mine, but i had the head off already, and mine was completely plugged due to the previous owner ("when was the last service done?" "Huh?") If you drain your system using the draincocks , then pull out your thermostat and pour in a 25% muriatic solution with water and let it sit for a while (15 min or a bit more) with the seacock closed, then reinstall the thermostat, connect everything, open the seacock, and run it until the engine is warm, it will flush it out. Repeat as needed; I think the operations manual says once a year. If you can find the operators manual online it will have the exact procedure which the above should be similar to. Use eye protection when mixing the acid; vinegar is too weak imo, and the pro descalers are overpriced compared to muriatic.

 

[Avi]

Thanks for the reply, it’s very helpful

 

[BobM]

If you are on the hard, leave the thermostat out until you are done flushing, as you won't be able to run the boat all that long. Some pH paper is handy to be sure you are back to neutral too.

 

[Avi]

Thanks for the advise I already did it, I think it’s successful, haven’t used the engine much yet