Yanmar 3GMD: Rydlyme or other marine descaler in older engine

[lecrappe]

Hello Cruisers,

I've recently acquired a 30 year old Yanmar 3GMD which runs at 67C (152.6F) at the crankcase when revved to 1800rpm after a few minutes. This is a little hot for my liking as I'd like to try and get it to 2000rpm if possible - beating into 25knt wind in a very narrow and shallow channel will be impossible otherwise.

When I replaced all the zincs recently (there are 3) I noticed a massive amount of white scale which I'm assuming is zinc oxide inside the engine block, so I'm wanting to descale. I bought Rydlyme as after some research it seems the most gentle.

My concern is some of this white zinc oxide is visible on the outside of the engine. Does this mean there is a small leak in the raw water system which if descaled will turn the engine into a leaky bucket?

If there are leaks, is it possible to seal, say if part there's a crack or corrosion in the engine block itself?


Thanks a lot for your help,
Brandon

[Compass790]

IMO you are putting off the inevitable if you dont descale. Do that then find the leak & yes it is possible to fix cracks but not always. Sounds too hot alright for a raw water-cooled engine. You will be getting lots more scale at those temps. Shouldnt be over 60C
Did you paint the engine?

[a64pilot]

You may not have leaks, that may be normal corrosion, maybe someone spilt salt water once etc.

I’d descale it and then look for leaks.
Spray on foot powder will find even the tiniest weeps and is easy to clean off.

[lecrappe]

Hi Compass790,

Thanks a lot for your reply. I'm planning on painting the engine after I've finished a "service". Thanks for your insight on scale at higher temps!

[lecrappe]

Oh wow, spray foot powder. I'll give it a go!

[Compass790]

Originally Posted by lecrappe

Hi Compass790,

Thanks a lot for your reply. I'm planning on painting the engine after I've finished a "service". Thanks for your insight on scale at higher temps!

Reason I asked about the painting is it looks like a rush job over coating hoses etc & was wondering if it's a cover up. But doesn't look too bad, maybe its just spillage as A64 suggests.
Our raw water cooled Yanmar ( YSM8 ) thermostat is set at 54C & our oil temp after 2hrs running fully loaded is only 59C & oil is normally hotter than the water after warmup. Can't tell you what water temp is as never put thermocouple on there but maybe someone with a 3GMD will chime in as to what their normal running temp is.
It's a good thing you spotted the problem as it will only get worse uncorrected.
Please let us know the result after you descale. I assume it's pumping plenty of water?
Good luck with it

[Compass790]

Some info on here :http://www.cruisersforum.com/forums/...le-188153.html

[BruceS]

I can't believe a diesel can run properly at that low a temperature?
Might be different for raw water cooled I guess?
My little 4108 that I used to have ran at more like 87-92 (or 188-197F?)

[a64pilot]

If a raw water cooled engine is allowed to run at normal temps I believe the calcium carbonate will precipitate out of the water and heavily scale the engine and will quickly clog cooling passages.
I’m unsure of the max temp but believe it’s about 160f.

It would likely be better if the engine ran hotter, but your limited to the lower temps

[Compass790]

Originally Posted by BruceS

I can't believe a diesel can run properly at that low a temperature?
Might be different for raw water cooled I guess?
My little 4108 that I used to have ran at more like 87-92 (or 188-197F?)

Yea Bruce all raw water cooled engines used in salt water have to run their cooling water temp below 60C or the salts precipitate out & build up in the cooling passages. If you put a fresh water thermostat in them they'll soon clog up.
They don't run "properly" as it's accepted wisdom that fresh water cooled engines last longer with the higher operating temp but having said that they can last a long time.
Ours still burns clean to the naked eye if you don't overfuel it
Don't have to take my word for it though. Check on google.

[mawtty]

I painted my 3GMD last summer .
It was still in the boat and i laboured with wire brush and rust converter.
I wish I had taken it out and sand blasted.
The white powder you see is corrosion that has not been removed and caused the recent repaint to fall away.
Horatio Hornblower the Horrible.

[Lepke]

When I was a kid in the 1950s, most gas engines were raw water cooled. When rebuilding one, you could find some water passages almost completely blocked. They also rusted out. It was common to replace the head because of wastage. I never owner a raw water cooled diesel, but if I did, I'd convert it.

I use Rydlyme in my 70 year old Detroits without issues.

[Compass790]

[QUOTE=Lepke;2933200]When I was a kid in the 1950s, most gas engines were raw water cooled. When rebuilding one, you could find some water passages almost completely blocked. They also rusted out. It was common to replace the head because of wastage. I never owner a raw water cooled diesel, but if I did, I'd convert it.

I use Rydlyme in my 70 year old Detroits without issues.

FYI Lepke. The raw water cooling doesnt seem too bad corrosion wise at all in our 39 year old yanmar . Maybe the gas engines you experienced weren't engineered as well. I thought about converting ours to fresh water cooled just for better operating temp but then thought why bother after I'd stripped & rebuilt it. The wet liner had a bit of corrosion but the block & head hardly any. We do fresh water flush it & I will do a descale when necessary with sulphamic acid but you have to do that with a heat exchanger. I do regularly check the anode.
I stole a quote from another thread re a raw water cooled engine life to illustrate my point. I'm assuming he described the engine correctly as a 3GM

Originally Posted by Bycrick

To make you feel more optimistic about your project. About ten years ago, the Yacht Club bought a used 3GM engine for one of our work boats. We had no idea of how many hours and there were vague rumors of being underwater sometime. Two years later (with a historic average of 2000 hours/year), the boat sank. Stayed underwater for several weeks. Finally raised, taken to a "mechanic" who let it sit in the shop for six months. We finally got it back. Thinking that really rebuilding it was a waste of time and money, we did the absolute irreducible minimum of work. Now, some 10k hours later, it’s still running just fine.

[Secondshift]

I flushed my 81' 2GM some months back using a dilution of muriatic (HCL) acid circulated with a small bilge pump I had on hand. The Rydlyme has additives as well as the HCL to assist in the process. They are not listed on the SDS but at three times the cost of a gallon of muriatic they must be pretty fancy.

Remember to pull your new zincs, thermostat and on the 2GM I had to obstruct a bypass hose. Plenty of people sharing on Youtube and suppose you already have a manual.

After my flush I circulated a neutralizing solution made with baking soda. Then clear freshwater. Think Rydlyme states simply flush with water.

The GM's are great motors with sleeved cylinders and the raw water cooled is a simple system. I wouldn't want to find room for a heat exchanger with my spares set.

Regards

[Secondshift]

Had another look at your photos. Photo 1 is on of your zinc anode mount. If the white powder is from a small saltwater leak the zinc housing can be resealed or replaced.
Unlikely to be a crack there.

The paint around the zinc mount bolt appears unbroken. Was this before you changed the zincs?


Regards