Rusty engines and sacrificial anodes
Q I’m the joint owner of a Cobra 850 and would be grateful for advice regarding the sacrificial anode on our Volvo Penta MD7B diesel engine.
We recently had a problem with the engine overheating and after checking the basics a marine engineer found some corroded debris clogging up a channel inside the thermostat housing.
After this was cleaned out the engine is now running properly again.
The problem we now have is that even with the owner’s manual the engineer could not locate or identify the sacrificial anode in order to replace it.
Does this engine model even have an anode and if so do you know where it is? Failing that, what should we do to overcome the inevitable corrosion issue?
STU DAVIES REPLIES:
As far as I can recall the VP MD7B doesn’t have a sacrificial anode in the engine. I have done an extensive search and read the manuals as well and no mention is made of one.
Don’t forget these engines are pretty old now and some corrosion will inevitably be apparent in the water passages and debris will have accumulated over the years of use.
It’s quite usual to use a product such as Rydlyme descaler to dissolve these salts in the engine and I would use this as a preventative measure on a regular basis. Perhaps every other year would be good.
Another thing I do on my own boat is use the raw water pump to pump an antifreeze mix through the system as part of the winter lay up procedure.
In my case, in Portugal, this isn’t for the antifreeze properties but for the anti-corrosion agent that it contains and this would be helpful in your case.