Engine Oil for Marine Diesel

[CapnHand]

I searched but did not find much. What type of engine oil is best?

I have used HD oil without detergent in the past. After discussing this with someone else, I'm thinking of using a detergent oil next time. My thinking is that non detergent oil is designed to let particulates settle in the oil pan. When the oil pan is drained, the sludge is removed. Since I pump the oil out, this is not good as sludge could accumulate in the oil pan. A detergent oil should be used to keep the particulates suspended so they can be removed by the filter.

I'm also thinking that the best time for an oil change is before laying the boat up for winter. This leaves the engine sitting in fresh oil, as opposed to old oil which could contain buildup of acids (combustion by products).

These are just opinions from an AFOC, I don't know for sure, I'm just trying to reason it out. What does everyone else think? Does anyone here work in the lube industry or have knowledge on this?

[Gene T]

Delo400 (I think that spelling is correct, using memory here) is what I have always used. Detergent oil is a good thing. Change oil at the end of season, if you have an end of season. Always run the engine after changing the oil to leave clean oil on all surfaces. Also run and warm up the engine good prior to draining the oil. Always change the filter at the same time.

[jrd22]

CapnHand- As was recommended above the Delo (diesel engine lubricating oil) is excellent and widely available at marinas, truck stops, parts stores. Shell Rotella-T is also excellent, I run it in all our trucks(Cat, Cummins, Intl., Perkins, Isuzu, etc.) and our boat. It is not as widely available at fuel docks as the Delo, so I carry a couple of gallons on the boat. 15-40 wt is what I run in everything and most major manufacturers approve it for normal air temps. These are heavy duty diesel oils made for continuous use; if I remember correctly they have a CE designation, not positive on that though. Excellent idea to change oil before layup.

[CapnHand]

Thanks guys. Is there any consideration needed for short term infrequent duty (as opposed to continuous use). My engine runs 20 minutes in / back to get me out of the marina two to four times per week. It only gets a long run a couple times per year.

[cruisingdream]

New oil designation for diesel engins (in the automotive world) is CI-4/sl

[pegasus1457]

As a newbie diesel owner, the first thing I did was to buy a couple of books from Amazon on diesel marine engines. The advice in these books is to stick with whatever oil was used in the engine by the PO. I can't remember the logic, but I think it has to do with the solvents in the different oils being incompatible.

[jrd22]

CapnHand- I think the best oil would still be the Delo400 15-40 or the Rotella-T 15-40. The pressures on the bearings is the same whether you use it for 15 min. or 24 hours. You need an oil that is designed for a diesel engine and the multi-viscosity will give you easier starts with full protection for the different seasons. It costs a little more than auto oil, but we are talking boats here, cost is no object-right? John

[Banshi]

I think this would be a situation where a full or partial synthetic might be in order. Something like Rotella 5W40 or perhaps even Amsoil 5W40 for diesel engines. A lighter weight will reach the parts needed and correct operating temperatures more quickly for an engine that will likely sit for long periods of time allowing the oil to drain out of critical areas. Amsoil also makes a full synthetic 15W40 for marine deisel use but the heaver oil will take a little longer to reach correct operating temperature and will be a little slower to get to those critical areas.

You might also like to know that higher price does not always mean better oil. The TDR (tdr1.com) recently tested several brands of oil from the cheapest store brands to the most expensive synthetics and had an oil engineer who favored the more expensive brands judge each one without knowing which he was looking. We are just talking about the chemical makeup of the oil unused to judge if the cost is justified and many variables apply that could not be tested but all in all most were considered satisfactory and price seem to have little to do with whether or not any particular oil met or surpassed the specifications.

One surprising above average oil was the Walmart store brand. Chances are that as long as you buy a diesel rated oil you will be fine. I run use the Rotella 5W40 in my Cummins powered dodge going 10000 miles between changes and I test the oil every second or third change to make sure there is no unusual wear occurring. I would think testing the oil in a marine engine every so often would be a good idea considering the environment it is being used in.

[USCGRET1990]

You are all pretty much right. Diesels are very dirty engines in reference to oil. A super high detergent is needed to keep the carbon and other crap in suspension. Then when you drain it, it goes out of the engine. If nothing else, stick with the truck engine stuff. If you don't run your engine all that much, then just change it a little more often. Not bringing an engine up to temp, allows moisture to stay in the oil. This will mix with other contaminents and make acid that will eat your engine inards. This is all quite a science and I am just posting a short response.

[jrd22]

Banshi- I would be very cautious about changing to a synthetic oil in an engine that has been running regular oil for a number of years. I have personal experience with a gas engine that blew ALL the synthetic out the seals in less than 40 miles of driving and we almost lost the engine. This was in a Dodge truck, 2001 model. I would check with the engine manufacturer before making this change. John