Some basic Diesel Engine / seawater questions

[ZZ13]

I know my gas engines pretty well but not really a darn thing about diesels other than what I've picked up reading here and there. Here are some questions:

What exactly would salt/sea water run through on a diesel engine setup? Is there cooling with manifolds, risers and elbows like in a gas engine? What parts are close/freshwater cooled and which parts get the seawater running through them? Is there a way to flush the seawater paths after each outing? What are the limited life parts that would need replacing on a more frequent basis due to seawater exposure (such as the manifolds, risers and elbows on a gas engine)? Are turbo aftercoolers cooled from seawater or closed freshwater system?

I am specifically interested in these answers for Cummins 6CTA. Thanks!

 

[fwebster]

The only parts handling sea water on a diesel are the sea water pump, the heat exchanger, maybe the transmission cooler, maybe the fuel cooler, maybe the after cooler and the mixing elbows where the cooling water is injected into the exhaust stream.

The sea water pump is bronze and isn't affected by corrosion, but is affected by wear so it may be a replaceable item.........I've got 1300 hours on mine and all I ever do is replace the impeller and cam.

The "maybe" parts the fuel, transmission oil are usually sea water cooled, but are brass/bronze and typically don't have corrosion issues.

The aftercooler may be "jacket" cooled meaning that antifreeze from the engine's cooling system passes thru it for cooling, or it could be sea water cooled. Sea water cooled ones do require maintenance and flushing, but typically don't have corrosion issues.

The exhaust elbows on my engines are bronze so corrosion isn't much of a worry. I don't know about Cummins, but I can tell you that I have never heard of anyone ever replacing a Cummins exhaust elbow for any reason.

Generally, the castings on diesel are massive and even if sea water passes thru them, they don't corrode away. Flushing is not necessary. Engine zincs, which are sacrificial anyway, are the only limited life parts due to sea water exposure. For this reason, you can kiss the usual Mercruiser corrosion worries goodbye when you move up to a diesel powered boat.

 

[ZZ13]

Thanks for taking the time to teach me some basics, Frank. I appreciate it.

 

[trit21]

I also depends greatly on the manufacturer of the boat as it relates to the exhaust elbow or exhaust showers as they are called and depending on the marine age of the boat (how long it has sat in the water not just how many hours are on the engines). For example, my exhaust is stainless and is designed in such a way that water will not sit in the exhaust shower elbow riser which will not permit water from back flowing into the turbo exhaust blades causing corrosion. THere are many things to look at in that regard and a great site to look into that, ask questions, post photos for others to review for you is boatdiesel.com OR sbmar.com. I have seen and heard on boatdiesel website that many manufacturers just did not make the exhaust with the best design and this has caused issues that have cost the 'new' owners of used boats quite a lot of money in replacement turbos or entire engines. But, as Frank has said, typically corrosion like what you are used to on Mercury engines is just not a major concern due to what touches raw water and the materials used.