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**Dockhead** · 06-07-2012, 08:56

I have a ton of rust in the fresh water side of my Kohler genset (3 cylinder Yanmar 1500 rpm engine). I have flushed and flushed with clean water but still comes out brown. Is that 2-part radiator flush safe for marine heat exchangers? Says it's safe for alu. It's a mild acid (oxalic I believe) with a second part which neutralizes the acid (probably baking soda). Opinions?

gjordan · 06-07-2012, 09:43

Dockhead, I doubt that the cleaner will hurt anything, but the more important question is why the freshwater side of your engine is so rusty? When I bought my last boat, the freshwater in the cooling system looked crystal clear, so I thought the previous owner had just been putting in freshwater rather than coolant. I ran it like that for a few monthes while I sorted out other things, and then drained it and put in coolant. A few weeks later the water was clear again. BAD SIGN! It turned out that the rubber pieces on each end of the heat exchanger had gone bad and I was running a raw water cooled Perkins 4-154. I have no idea how long the engine was running like that, but Im sure it didnt do the engine any good. Your Yanmar may have a bad heat exchanger, or may have had one in the past which would account for all of the rust. Check your manual to see if you have zinks in the system and replace them. While checking the exchanger, pull the tubes and clean them. A 22 caliber rifle cleaning brush works very well. Sorry for being so long winded.____Grant.

hellosailor · 06-07-2012, 10:23

Dockhead, I've heard of oxalic (which eats rust) and more commonly citric acid being used as a radiator cleaner. Citric acid is sometimes sold as "sour salts" in the US, in supermarket spice sections, because it has long been used to "boil out" aluminum coffee percolators. As has vinegar been used.

Most anything you can buy in an auto store for radiator cleaning will be safe when used as directed, i.e. marked safe for aluminum or not, with or without a neutralizer afterwards.

There are lubricants, anti-rust ingredients, other "stuff" in coolants so once you get it flushed out, refill with a proper coolant not just water, and if you have to mix the coolant with water, used distilled or de-ionized not just tap water. Makes a BIG difference if there are any minerals in your tap water.

But "rust" in the coolant isn't always rust, either. When the traditional "green" a/f has been used, then someone tosses in the new "orange" permanent a/f, sometimes the two react and produce brown sludge. Sometimes they eat gaskets, too. So before you refill, try to find out what was last used, and whether the new stuff is compatible with your engine gaskets. (When it is, it IS a better product.)

MarkSF · 06-07-2012, 10:38

Quote:

Originally Posted by hellosailor

Dockhead, I've heard of oxalic (which eats rust) and more commonly citric acid being used as a radiator cleaner. Citric acid is sometimes sold as "sour salts" in the US, in supermarket spice sections, because it has long been used to "boil out" aluminum coffee percolators. As has vinegar been used.

Most anything you can buy in an auto store for radiator cleaning will be safe when used as directed, i.e. marked safe for aluminum or not, with or without a neutralizer afterwards.

There are lubricants, anti-rust ingredients, other "stuff" in coolants so once you get it flushed out, refill with a proper coolant not just water, and if you have to mix the coolant with water, used distilled or de-ionized not just tap water. Makes a BIG difference if there are any minerals in your tap water.

But "rust" in the coolant isn't always rust, either. When the traditional "green" a/f has been used, then someone tosses in the new "orange" permanent a/f, sometimes the two react and produce brown sludge. Sometimes they eat gaskets, too. So before you refill, try to find out what was last used, and whether the new stuff is compatible with your engine gaskets. (When it is, it IS a better product.)

If you want to go with one of the new long-life coolants, I suggest a hybrid-technology coolant which has better backwards compatability with the green. Examples are Valvoline Xerex G-05, and then most of the car manufacturers are using hybrid coolants now (BMW Blue, VW Pink, and so on). The Valvoline is the easiest to find as far as I know.

**Dockhead** · 07-07-2012, 14:13

Thanks, guys, for the good advice.

The brown sludge was one of two things - either silicate in original green antifreeze precipitated out when I had the genset professionally serviced, including change of coolant, when I bought the boat 3 years ago. The engineer put in pink, and might not have flushed out the old green very well. Or, rust because I never changed the anode in my 3 years of ownership. Or, both

In any case, I have now flushed the carp out of it - at least 12 flushes. I used that 2 part radiator flush stuff, and flushed 3 times after part two. Filled with 50/50 deionized water and pink coolant. I'll keep an eye on it and hope it works now. In any case, the genset is running normally at the moment.