Are you converting this engine from
raw water cooling to a closed circuit unit with a
heat exchanger?
I've done this to several engines over the years.
The best solution I've found is to use muriatic acid through all the water passages that
salt water had previously touched. Even on iron blocks, otherwise it's questionable that vinegar would do the job. If your looking to convert to a closed system on the engine even the smallest amount of residual
salt in the system will cause oxidation over time.
The bronze/brass
heat exchanger tubing bundles are also more efficiently cleaned with muriatic acid, just take care in the use and
storage of the acid, take all the common sense
safety precautions when using it.
If your using it to clear mineral deposits out of an iron block make sure to neutralize the acid and flush with plenty of clean, mineral free water once you've removed the acid, then get your antifreeze/rust inhibtor mixture into it as soon as possible. The newly etched iron will start to rust in short order.
Vinegar is OK for light mineral buildup but wont remove heavy scaling, I use it more for seasonal
flushing use on my raw water systems.
One Atomic 4 I rebuilt for a friend had over an 2 inches of accumulated mineral sediment in the cylinder
cooling jackets, this means that section of the cylinders was not being cooled, some smaller passages were clogged. Once some physical poking was done it was dipped in muriatic acid, this cleaned it completely. Few other agents would have done the job that efficiently.
If your engine was raw water cooled for 20 years I would suspect it has just as much build up in it.
The cylinder block does not transfer as much heat as the
head does, but it still needs complete and consistent cooling as uneven cooling in a cylinder bore can lead to cylinder warping and accelerated wear.
Making sure your cylinder
head cooling is free flowing and clean is twice as important, it passes
exhaust gasses through the
ports and sees a significant heat load.