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Just sorted a problem in my Yanmar 3GM30.
It has raw water cooling and although water was coming out, the symptom was steam issuing from the exhaust over 2200 rpm.
Replaced the pump impeller and checked the flow to the pump but problem persisted.
Further investigation showed the thermostat was full of lime flakes.
Inside the thermostat housing was more lime scale and I could see the same into the head as well.
The hose to the engine was partially blocked and the bypass 'T' fitting was completely blocked.
Acid is good for getting rid of lime but I was a bit concerned about using it so I trialled a few flakes in vinegar.
The flakes dissolved in about 2 hours so I bought 4 litres from a well known supermarket and filled the engine cooling system.
After about 4 hours the results were not exactly amazing but on tasting the vinegar (unused) I found it not to have the bite which the original stuff had.
I bought good stuff (Skipping Girl) and left it in for 8 hours, flushed it again with a new lot and left it overnight.
The results were very good and the engine pulls 2500 rpm in the pen with no steam and everything in order.
Think I will do it every year or so if the thermostat show signs of build up.
Cheers,
Tom
(I am using it in the toilet outlet too!)

Gee, that is a lot of scale. I guess some bits of the motor must have been getting pretty hot for steam to be coming out. Steam does not sound good. Unless it is a steam engine.

troppo

Salt precipitating out because the engine was running too hot? Apparently this is a common problem with raw water cooled diesels.

I don,t know how suitable it would be on a diesel but an old mechanic got me to use a litre of phenyl in the car radiator for a couple of hundred k,s to clean things out and it worked a treat.

It was lime (calcium) rather than salt deposit and the overheating was not in the engine but the exhaust.

The bypass was blocked so all water had to go through the thermostat which passes enough for engine cooling but not enough to cool the exhaust.

The engine needed cleaning out for sure but the blocked line was the big problem creating the steam.

Just thought you might all like to know that vinegar (not cheap stuff!) works getting rid of the lime scale.

Cheers,

Tom

Don't guess these things, why not contact a diesel mechanic?

Tom, what you've hit on is the correct solution. (so to speak)
In the diesel the thermostat is set to 55 degrees, that is very low and they will not run efficiently. Diesels like to be run hot, and hard. Its a compromise between efficiency and simplicity.
At 80 degress C the salt hardens to a crystalline form that doesn't re dissolve back in the water. That is the scale that you are looking at.
I had a Hatz branded as a BMW marine diesel. 12Hp.
I used to regularly use a solution of 1 to 1 vinegar and water. Yearly is about right.
If you just want to clean one part such as a thermostat try this solution and heat it to almost boiling and it will "Pickle" the parts in about 30 minutes. Power stations use the same system in the boilers
One part that used to really scale up was at the entry to the motor where brass fittings join the steel block or head.
What you should also look at is the mixing elbow where the cooling water enters the exhaust. The holes in the mixing elbow rust up and stop the flow. A mixing elbow usually lasts about 2 to 5 years.
90% of the water entering the engine goes straight down the exhaust to cool it and muffle it. At 2000 rpm the Hatz used to put through about 20l per minute. the Volvo uses one and a half times that! You can check that by putting a bucket under the exhaust or filling a bucket with fresh water and taking the hose from the sea cock and taking the water from the bucket.

I don't think phenyl will work its only organic. I've had no experience with it.

For what its worth.
Greg.

Hi Greg,
The engine wasn't actually getting hot but it did have lime scale in it (not salt).
Yes, I found the lime scale on the bronze fittings too, also in the hoses.
The straight vinegar cleaned up the thermostat in about 2 hours at room temp.
Cheers,
Tom

I use saltex for my Tinny and outboards, it is great stuff

http://www.saltx-saltremoval.com/SX50.html

The first engine service I did on my Yanmar 2GM included replacing the cooling water hoses. I was surprised at how stiff they felt, and they actually crackled when flexed, since they were so full of scale. The increase in exhaust water flow was amazing after a day of vinegar soaking in the engine CW system.

Cheers, Graeme

My Mechanic recommends flushing the cooling system out with vinegar and freshwater once a year to stop salt build up .

Cheers Bear