Marine diesel engine oil... what type is best?

Question for you all… what sort of engine oil do you use on your ship?

BP Castrol just came out with some new 80 BN oil that’s geared toward slow steaming ships using high sulfur fuel.

Is anyone out there working on slow steaming ships using lower BN oils?

The reason I’m asking is because when ships are slow steaming, as they tend to do these days to increase efficiency and save fuel, the engines operate at a lower temperature. Temperatures inside the engine may then drop below the “dew point” of the sulfuric acid formed as a result of combustion, which would then degrade the condition of the liner surface resulting in pitting and wear due to cold corrosion.

The higher BN (base number) oils are able to essentially absorb more of this acidity than lower BN oils. Additionally, more acid is produced when combusting high sulfur fuels.

Ash is also a factor.

If you’re operating at high engine poiwer using low sulfur fuel in an emissions control area, such as the Baltic Sea, you may be leaving ash deposits inside your engine. Essentially, if there is a mismatch between lubricant base number and fuel sulphur, the unused additive may form hard piston crown deposits which could result in potential damage to liners through bore polishing and scuffing.

Anyway, this new 80 BN oil from Castrol seems like useful stuff for ships that operate under slow steaming conditions and I was wondering if anyone has tried it, or is having issues with some of the lower BN oils under slow steaming conditions…

Would be interested in hearing your opinions…

Base numbers are all about balance. High base numbers attack bearings. Ideally you start with the minimum base number that allows your oil to reach the end of its operating life before requiring a change or before being consumed. Many larger engines don’t actually require oil changes during their lifecycle but oil analysis is critical because you need to monitor the TBN. If the engine isn’t burning oil fast enough (light load) you may need to run a higher TBN oil in order to prevent the oil from becoming acidic within its lifecycle. But, you want to run the minimum TBN to get you to the end of our oil’s lifecycle. You don’t want to have to change the oil because it has fallen out of spec. That is VERY expensive.

Using a high BN i.e. and 80 when slow steaming is critical. If not, Corrosive wear of liner surfaces and piston rings is likely to occur, severe cases may require liner and ring reconditioning or replacement. This is because the Lubricant is in contact with hot liner surfaces and exposed to acidic gases for significantly longer. This can degrade the oils ability to neutralise acids and increases potential for oxidative degradation and deposit formation

As engine loads fall significantly less cylinder lube oil is consumed and available to lubricate liner and pistons. Under extreme conditions this reduced level of lubricant may result in oil film breakdown, the onset on boundary lubrication conditions and mechanical as well as corrosive wear.
•Severe corrosive wear could result in liner/ring replacment.Total cost of liner replacement including parts and labour is in the region of $40,000 to $65,000 [U]per unit. [/U]
•Replacement or reconditioning of liners creates risk of disruption on vessel operation and schedules. It usually takes a day to replace or re-hone a single cylinder. This work is generally carried out by OEM approved sub-contractors.
•The hassle factor in arranging liner repairs or replacement is therefore extremely high and creates opportunities for sailing schedules to be compromised
•Large container vessels only tend to be alongside for 6-8 hours and they can incur significant port fees if they block a container discharge berth for longer than this

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