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Old 28-07-2020, 10:14   #1
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Engine descaling - good or bad?

A number of people have told me that it is a good idea to occasionally descale the coolant system on my Yanmar diesel. I bought the boat in Nov 2019 (2010 Leopard 46 cat), and I don't know how many hours are on the engines. I have been planning on making my own descaling fluid circulator (5 gal bucket, pump and hoses) and doing it myself. I will also use it to descale my air conditioners.

I asked a mechanic at a local company that does a lot of Yanmar work and he said they don't descale because they have had bad experiences where there were coolant system leaks after descaling. Instead, they disassemble, inspect and descale / service / replace components as needed.

I am guessing that coolant leaks after descaling were pre-existing problems temporarily masked by scale deposits and they would have failed soon anyway, but that's just my guess.

What are your thoughts?

thanks,
Pat
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Old 28-07-2020, 23:46   #2
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Re: Engine descaling - good or bad?

I assume that your Yanmars are not raw water cooled, so the only paarts that should need any such treatment are the heat exchanger and raw water pumps and associated plumbing. Cleaning the HX now and then is a good idea, and circulating some descaler through it should not harm it.

The routine disassembly that your mecho describes seems unnecessary to me... but a good money spinner for him! Changing the coolant at the prescribed intervals and maintaining any anodes in the HX should keep everything healthy for many hours.

When we had a raw water cooled BMW diesel we descaled it with HCl on a regular basis... and it still got choked with deposits. Grrr... seems that some areas didn't get much benefit from the acid, whilst other parts were nice and clean. Never solved that one!

Good luck with your efforts,

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Old 29-07-2020, 06:18   #3
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Re: Engine descaling - good or bad?

Jim - Correct, I would be pumping the descaler through only the raw water portion which includes the HX. That is where I would expect most of the build-up of deposits. I have seen videos showing them getting pretty clogged up.

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Old 29-07-2020, 06:27   #4
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Re: Engine descaling - good or bad?

What Jim and Pat said +1

If in doubt, follow the maintenance schedule as per the Yanmar operation manual.
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Old 29-07-2020, 10:46   #5
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Re: Engine descaling - good or bad?

Have had Yanmar for 10 years I descale very two - three years BUT the gaskets at the heater exchanger should be changed every 5+ years per my Yanmar guy who is no crook. Big PIA job but easy done by a pro.
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Old 29-07-2020, 13:59   #6
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Re: Engine descaling - good or bad?

I have 2 Yanmar 4LHA STP engines on my PowerCat. Mack Boring the Yanmar distributor fo the NE US used to host hands on diesel classes where you actually worked on your model engine. I took the course and they highly recommended Rydlyme. I now use it periodically and also clean out the A/C units with it. It has made a big difference and completely solved an overheating issue ( when running hard). Itís also non toxic to the environment so you can just dispose of it easily.
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Old 29-07-2020, 20:21   #7
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Re: Engine descaling - good or bad?

I would NOT be putting anything like that into an engine with alloy parts. That is just asking for trouble.
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Old 30-07-2020, 04:46   #8
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Re: Engine descaling - good or bad?

Quote:
Originally Posted by Looking4Neptune View Post
A number of people have told me that it is a good idea to occasionally descale the coolant system on my Yanmar diesel. I bought the boat in Nov 2019 (2010 Leopard 46 cat), and I don't know how many hours are on the engines. I have been planning on making my own descaling fluid circulator (5 gal bucket, pump and hoses) and doing it myself. I will also use it to descale my air conditioners.

I asked a mechanic at a local company that does a lot of Yanmar work and he said they don't descale because they have had bad experiences where there were coolant system leaks after descaling. Instead, they disassemble, inspect and descale / service / replace components as needed.

For our engines and genset, we treated these as two complementary processes. I de-scaled a few times myself using either Rydlyme or Barnacle Buster, but didn't consider that a substitute for real off-engine inspection and service as mandated by the service manuals.

-Chris
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Old 30-07-2020, 07:55   #9
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Re: Engine descaling - good or bad?

I would only descale if I thought there was a problem! I took off my heat exchanger/exhaust manifold last month to replace a cracked seawater flange. The engine is 19 years old and has around 3000 hours on it. There wasn't any scale in the heat exchanger.

From a scale deposit point of view; scale forming is greatly affected by skin temperature in the heat exchanger and that is greatly affected by flow. So keeping you strainer clean and pump impeller good greatly reduces scaling. Keep in mind that engine temperature (the fresh water) and exchanger skin temperature are not the same thing at all.
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Old 30-07-2020, 08:23   #10
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Re: Engine descaling - good or bad?

I change coolant every other year and remove the heat exchanger tube pack when I do, it’s six bolts and easy to do, means you replace two O-rings, so why not do it?
You could just pop off one end and clean the tubes and reinstall the cap a lot easier than jury rigging up some kind of pump and bucket, hoses etc, and then where do you store these items for another year or two when you do it again?
I’ve not seen any significant scaling either.
I strongly suspect that pumping these solutions around work mostly because there isn’t much there to clean to begin with, and that they do cause some harm to the aluminum bits in the engine.

I’ve briefly thought about putting in a T to my raw water line and flushing the engine with it running with fresh water with the seacock closed, that would leave only fresh water in the engine when I’m just sitting, but haven’t done it because I’ve not see any corrosion or scaling yet.
My engine is a 1987 model, so that makes it 33 years old, if it hasn’t rotted out or scaled up yet, it’s not likely to.
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