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Old 05-11-2021, 07:26   #1
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Yanmar 2GM sudden severe corrosion

Take a look at the photos of what looks like deformed metal, not just rust. Only under the Head gasket joint.
Is it rust or galvanic corrosion? cause? could be that I neglected to change the zinc sacrificial anodes last fall (kicking myself for cutting corners again)

There is a galvanic isolater on a newly installed Lifepo battery bank and power upgrade to Victron inverter/charger, new alternator and 660 watts of solar.
The boat is only on shore power occasionally as it is on a mooring.

no change in power, no water in oil or leaking from head gasket
If it looks this bad outside I'm afraid of whats going on inside!
May need to consider alternate propulsion. But its running fine right now.
Has anyone seen anything like this?

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Old 05-11-2021, 07:47   #2
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Re: Yanmar 2GM sudden severe corrosion

I don't see a link to photographs.
Never let anything mechanical know that you are in a hurry.
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Old 05-11-2021, 10:05   #3
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Re: Yanmar 2GM sudden severe corrosion

album of 4 images and thanks for responding

individual photo links:
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Old 05-11-2021, 10:38   #4
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Re: Yanmar 2GM sudden severe corrosion

A little hard to tell what is what in the pics. But the rust near the silver paint is not totally uncommon. The paint has flaked off. It has nothing to do with how good the engine is inside.
However, it seems to me that there is too much dampness or a leak in the engine compartment. Engines that are kept dry and run often and kept clean dont look like that. I have seen neglected engines that look nearly entirely that rust color all over and still run well. Fortunately cast iron is less prone to deep corrosion than steel.
Clean it, paint it. keep it dry.
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Old 05-11-2021, 13:06   #5
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Re: Yanmar 2GM sudden severe corrosion

I would say your head gasket is leaking though I know you said its not.
Look at you anodes but I doubt very much they are the cause of that problem. I think I see some salt crystals in one pic. Thats a raw water cooled engine IIRC.
That paint flaking off around the head gasket joint happened the same on our YSM8, it was the head gasket. There was no noticeable power loss but I did see water spraying out eventually but a while after the paint started flaking off. I think the leak got worse.
My advice is replace the gasket & use gasket cement on the head gasket, Loctite 518 is what I'm familiar with & it works very well.
You can even re-use the old head gasket if you use 518 on it but safer to get a new one. Others will say you cant but they will be people who have never actually tried using 518 on a used head gasket I'd wager. I have & can vouch for its effectiveness.
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Old 06-11-2021, 13:52   #6
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Re: Yanmar 2GM sudden severe corrosion

NEVER connect to shore power without using an isolation device. In my case it was a 2KVA isolating transformer. Before double-insulated tools became the norm--builders used them and because there are no moving parts, there are a few about in good condition. They weigh about as much as a lead-acid starting battery.

There are other types of device available too, much lighter. But if you do not use such a device, your vessel becomes part of the power earthing system--and not only YOUR faults but everyone else's exits via your contact with the salt water wherever it occurs. In your case your engine is probably part of the earthed equipment in your vessel.
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Old 06-11-2021, 16:33   #7
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Re: Yanmar 2GM sudden severe corrosion

Water jacket leak past head gasket.
Quite commn on raw water cooled engines.less so on those with an interccooler.

The Yanmar GM series head has inadequate lands outside the waterways on the head.
Providing the coolant is not getting into the cylinder it's not a serious matter, but will need the head milled and the head gasket replaced.
I've had it happen twice on the same engine, allowing "professionals" to correct the problem is not to be recommende. They just changer the head gasket at an exorbitant rate..
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Old 06-11-2021, 17:15   #8
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Re: Yanmar 2GM sudden severe corrosion

It really seems like a head gasket job. If the engine has had a head job in the past then the problem may have been that the normal follow up head bolt/nut tightening may have been neglected. This secondary tightening is usually carried out after some nominated period of engine operation. Check your service manual. (25 hrs ?) However, once water secretes under the gasket, then it's usually too late and the gasket should be replaced and the two surfaces checked. Removing a head gasket requires care and the use of a vacuum cleaner to prevent any bits of the scraped off gasket material from falling into the engine cooling galleries or the con rod holes.
Some engine manufacturers don't encourage the use of gasket sealants but Hylomar is a typical product. You will need a good torsion gauge wrench. Measure the torsion values when removing the head (see manual for correct sequence). These values should be near identical. Discrepancies may reveal the nature of the problem. Follow the correct sequence when replacing the head.
Removing and assessing an engine head is usually a job for professionals as they can do assessments of the valve seats and the head surfaces and can carry out the repairs in specialised workshops. Plus you should get a warranty. Not cheap, particularly for Yanmar parts, but well worth it.

Regarding the anodes: yes, they do need very regular replacement. They are there to protect the cast iron engine block interior surface. They do nothing for the outside surface though as an electrolyte such as salt water is required on the surface to be protected.
Another issue is the thermostat. (Expensive!) but they should be checked regularly as well. Particularly if there is any rubbish in the water.
A common practice for these direct salt water cooled engines is to ensure fresh water flushing after use. Run until the exhaust water is fresh, not salty. This entails a bit of plumbing but it can really make a big difference to longevity. Most engines spend 99% of their life just "resting" but with salt water in the block, the corrosion does not stop. You may even consider a method of draining water from the block after the engine has cooled down. There may be an issue with the thermostat. Food for thought.
I have an ancient 1GM used as a genset and for running various compressors/pumps and have recently had the head done. Although not really familiar with the 2GM I would be doing a thorough check on the exhaust manifold as well. There are better alternative products.
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Old 07-11-2021, 17:59   #9
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Re: Yanmar 2GM sudden severe corrosion

I recently aquired a Freedom 28 with a Yanmar 2 GM, which has a heat exchanger, with antifreeze / FW in the engine. Was this an option?
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Old 08-11-2021, 20:49   #10
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Re: Yanmar 2GM sudden severe corrosion

If the model #has an F, then it has fresh water / coolant radiator (still uses raw water to cool exhaust through elbow). Such as 2GM20F.
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