7. Lubricating Oil System
7.1 Lubricating oil requirements
7.1.1 Engine lubricating oil
The lubricating oil must be of viscosity class SAE 40 and have a viscosity index (VI) of minimum
95. The lubricating oil alkalinity (BN) is tied to the fuel grade, as shown in the table below. BN
is an abbreviation of Base Number. The value indicates milligrams KOH per gram of oil.
Table 7-1 Fuel standards and lubricating oil requirements, gas and MDF operation
Fuel S content, [% m/m]Lubricating oil BNFuel standardCategory
0.410...20
GRADE 1-D, 2-D, 4-D
DMX, DMA, DMB
DX, DA, DB
ISO-F-DMX - DMB
ASTM D 975-01,
BS MA 100: 1996
CIMAC 2003
ISO 8217:2017(E)
A
0.4 - 2.015...20
GRADE 1-D, 2-D, 4-D
DMX, DMA, DMB
DX, DA, DB
ISO-F-DMX - DMB
ASTM D 975-01
BS MA 100: 1996
CIMAC 2003
ISO 8217:2017(E)
B
If gas oil or MDF is continuously used as fuel, lubricating oil with a BN of 10-20 is recommended
to be used. In periodic operation with natural gas and MDF, lubricating oil with a BN of 10-15
is recommended.
The required lubricating oil alkalinity in HFO operation is tied to the fuel specified for the engine,
which is shown in the following table.
Table 7-2 Fuel standards and lubricating oil requirements, HFO operation
Fuel S content, [% m/m]Lubricating oil BNFuel standardCategory
4.530...55
GRADE NO. 4D
GRADE NO. 5-6
DMC, RMA10-RMK55
DC, A30-K700
RMA10-RMK700
ASTM D 975-01
ASTM D 396-04,
BS MA 100: 1996
CIMAC 2003,
ISO 8217:2017(E)
C
In installation where engines are running periodically with different fuel qualities, i.e. natural
gas, MDF and HFO, lubricating oil quality must be chosen based on HFO requirements. BN
50-55 lubricants are to be selected in the first place for operation on HFO. BN 40 lubricants
can also be used with HFO provided that the sulphur content of the fuel is relatively low, and
the BN remains above the condemning limit for acceptable oil change intervals. BN 30
lubricating oils should be used together with HFO only in special cases; for example in SCR
(Selective Catalyctic Reduction) installations, if better total economy can be achieved despite
shorter oil change intervals. Lower BN may have a positive influence on the lifetime of the
SCR catalyst.
It is not harmful to the engine to use a higher BN than recommended for the fuel grade.
Different oil brands may not be blended, unless it is approved by the oil suppliers. Blending
of different oils must also be validated by Wärtsilä, if the engine still under warranty.
An updated list of validated lubricating oils is supplied for every installation.
DBAE248994 7-1
7. Lubricating Oil SystemWärtsilä 31DF Product Guide
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