Engine mount corrosion

[Fourbees]

Our Volvo Penta 2020 has been diagnosed with a corroded engine mount, aft, starboard side. It's only three years old (as is the whole boat). The technician servicing the engine asked whether it had been in contact with salt water, but it has not. Could it be galvanic corrosion, and what can I do?

 

[timtap]

It could be !!!! especially if the mounting is zinc plated. Check all earth bonding cables from .... mounts to engine...,engine to gearbox.....gearbox to outdrive or sterndrive/steering gear....., sterngear to anodes...

 

[timtap]

Further to my first message.... if the mountings are on steel bearers make sure the bearers are earth bonded too !!!!

 

[VicS]

[ QUOTE ]
Could it be galvanic corrosion, and what can I do?


[/ QUOTE ] Galvanic corrosion is what you get when two dissimilar metals are immersed in an electrolyte , eg salt water, so technically no it is not galvanic corrosion.

However what can you do about it

If it is so badly corroded that it is now structurally deficient then you have no alternative but to replace it and its mate if they really do only go in pairs.

If it is only surface rust then clean off all the rust, apply a chemical rust remover, clean again and reapply the rust remover. repeat until you have got rid of all the rust then paint. For convenience, not because it is particularly good, use Hammerite primer followed by several coats of Hammerite. (if you have money to chuck away use the Volvo paint to match the engine).

Is there any wiring eg earthing wires or anode bonding wires connected to it?

 

[timtap]

Try with a electricians meter set to ohms and check the signal between the various components in earlier messages. engine rooms often sweat but the engine mounts on volvo engines which i believe are indeed zinc plated will attract the deterioation that normal anodes would be subjected to if bonded correctly. Therefore it seems relitively likely that the bonding circuit may have broken down somewhere so this is the area to check first.

 

[steve28]

maybe a leak from the exhaust or from the antisiphon device, i had this for a while and it made the mount rust in a matter of weeks.

 

[Fourbees]

I haven't noticed any wires attaching to it - being the aft one, it's quite hard to get a good close look at it. I'll have to look for wires next time I'm down there though. In view of timtap's comments there should probably be wires everywhere - do you agree?

 

[Tranona]

No, there are unlikely to be wires anywhere. You do not say what boat it is in nor whether it is saildrive or conventional.

Many modern boats do not have external anodes because they don't have a galvanic problem. Mounts would not be included anyway because they are isolated in part by rubber. Galvanic corrosion as VicS says affects parts that are exposed to the seawater like skin fittings, propellers and shafts.

The rusting on your engine mount is almost certainly caused by water dripping onto it from the intake filter, antisyphon valve or connecting pipes. The intake filter is almost certainly on the starboard side above the engine on a bulkhead because the water pump is on that side. The anti syphon valve is in the water exit pipe from the engine to the injection point in the exhaust manifold. As it has to be above the water line it will be above the engine.

It is probably only surface rust on the mount which can be cleaned off and repainted. Find the source of the water first, stop that - for example many people fit an overflow bottle from their anti syphon valve to catch the drips. Check all of the clips for tightness.

Hope this helps

 

[Fourbees]

She's a Feeling 32, conventional propshaft rather than saildrive.

 

[Tranona]

That makes it easier to replace if you have to. At first I thought £500 was high, but when I went through what was involved in my mind I got to 4-5 hours labour, assuming half the boat did not need dismantling to get at everything that needs disconnecting to lift the engine.!

I still think water dripping on it is the problem as others have noted, so a couple of hours of you crawling around doing basic checks could save you a big bill.

Good luck

 

[Fourbees]

Thanks!