Internal engine rust

[doca]

For the first time I am carrying out some routine engine maintenance, e.g., checking thermostat, impellor, etc, as recommended by the owners manual. Its a Volvo Penta MD11c , raw water cooled, and a coating/staining of rust is evident on the inside. Is this to be expected, and if so, how much of it is acceptable ?

 

[Talbot]

check that you have the correct thermostat for raw water cooling (it is a much lower temperature than used for fresh water) consider use of a de-scaler.

 

[Topcat47]

On an engine of this vintage I'd be surprised if there were no internal rust. It's an iron casting and salt water is very corrosive. You say this is your first attempt at routine maintenance, so I guess it's an older boat. How long have you had her?

I flush my engine with ~ 5gals of FW on lay-up and fill it with antifreeze (which contains inhibitors).

The problem with rust is that it is many times the volume of the base metal and if you're unlucky this will constrict the waterways. I can't remember if the MD's had intenal anodes but my Yanmar does and this needs regularly renewed.

 

[doca]

Its an 1979 boat. It has been mine for the past two years and I know it has been well looked after in the past, including a maintenance check just before I bought it. It has been faultless to date and I intend to give it plenty of TLC.

 

[Brian_Moffat]

If you only have a light coating or staining (if you wipe it with your finger it's brown and dusty -

Congratulations - your engine is identical to every other engine.

It's normal - a brand new engine will have the same coating inside of three months.

If, on the other hand, you can prise bits of rust out - that is different - engine inspection time.

regards

Brian

 

[VicS]

That sounds normal.
What you must be aware of is the tendecy for the inlet waterways in the exhaust manifold to become blocked. There are two smallish passages that run from the inlet connection half way along the underside of the manifold to the heads. One of these is longer than the other and is the most likely to become blocked. They are not too difficult to unblock with a bit of stout wire but you need the manifold off of course and you will need a new gasket to refit it.

Choking of the water ways in the cylinder blocks is another problem and also blocking of the smallish water ways between the heads and the blocks. Unblocking these is of course a major job. but the occasional flush through with a central heating boiler descaler should help to keep them clear. That's an acid based descaler not just a heating system cleaner. Some use a hydrochloric acid based brick cleaner but I would be very cautious about using that too frequently. Neither will unblock something that is choked solid though.

Make sure you can get a good flow of water from both of the cylinder block drains.

When the engine is running check with a contact thermometer if you have one or at least by feel that both blocks and both heads are the same temperature. If one half of the engine is hotter than the other it indicates a lack of coolant flow through that half. You cannot rely on the temperature guage as it is possible to have one half overheating while the other is overcooled. A regular fluctuating reading of the temperatue gauge is an indication that the system is getting seriously choked up.

You've probably guessed that we have had a fair bit of trouble with the cooling system of an MD11C.

 

[Brian_Moffat]

Hydrochloric does work a treat though - it may need a couple of run throughs (and you can do it both directions on a really stubborn one)

Just one thought occurred to me .... Nobody's lost a bit of impeller recently ... have they?

It's great fun trying to fish those little devils out of the heat exchanger - and they don't half play havoc with your coolant flow.

regards brian