Cylinder oils from BN 40 to BN 140.
For low-speed two-stroke crosshead engines. Six base numbers so the feed can be matched to the fuel actually in the tank rather than to whatever is on board.
CYN 50 BN 100 is WinGD validated
Listed in Validated Engine Oils for WinGD Engines, Version 18 (January 2026) — valid for WinGD X, X-DF, X-DF-A, X-DF-M, RT-flex and RT-flex-DF engines, plus Wärtsilä RTA / RT-flex / X and Sulzer two-stroke engines. CYN 50 BN 70 additionally holds an Everllence No Objection Letter.
See the documentsChoosing a base number
BN is matched to fuel sulphur content. Running too high a BN on low-sulphur fuel is as damaging as running too low a BN on HFO.
ULSFO / distillate (≤ 0.10 % S)
BN 40 Cat II ULSFO
Low-sulphur operation; excess BN causes deposit build-up.
VLSFO (≤ 0.50 % S)
BN 40 Cat I · BN 55
Balanced neutralisation for compliant fuel.
HFO (up to 3.50 % S)
BN 70 · BN 100
Higher reserve to neutralise sulphuric acid formation.
High-sulphur HFO with scrubber
BN 100 · BN 140
Maximum neutralisation for sustained high-sulphur running.
Guidance only. Always follow the engine builder's prevailing cylinder lubrication instructions and feed rate guidelines for your engine type.
Typical properties
| Product | TBNmgKOH/g | KV 100°CcSt | KV 40°CcSt | VI | Flash°C | Pour°C | Densityg/ml |
|---|---|---|---|---|---|---|---|
| CYN 50 BN 40 Cat I | 36.5 | 19.00 | 211.8 | 101 | 258 | -24 | 0.916 |
| CYN 50 BN 40 Cat II ULSFO | 40.0 | 19.10 | 220.6 | 98 | 266 | -18 | 0.920 |
| CYN 50 BN 55 | 55.0 | 19.10 | 218.2 | 99 | 260 | -18 | 0.925 |
| CYN 50 BN 70 | 70.0 | 19.05 | 219.7 | 98 | 264 | -21 | 0.920 |
| CYN 50 BN 100 | 100.0 | 19.50 | 222.6 | 100 | 272 | -21 | 0.945 |
| CYN 50 BN 140 | 140.0 | 19.60 | 218.0 | 103 | 274 | -18 | 0.955 |
All grades SAE 50. Performance claims: MAN ES and WinGD. Typical values from Sinova Group technical data sheets (Form 002-EN, 5 January 2025); properties are based on current production and may vary within specification.
Questions we get asked
What is cylinder oil used for?
In a two-stroke crosshead engine the cylinder oil is injected through quills onto the liner, timed to the piston's passage, and used once. In the seconds it exists on the liner it neutralises the sulphuric acid formed from fuel sulphur, holds a film under high load and keeps deposits off the ring pack and piston crown. It never returns to the sump; the crankcase runs on a separate system oil.
Why a crosshead engine uses two oilsWhich base number (BN) should a cylinder oil have?
The fuel decides. Base number is the oil's alkaline reserve, measured in mg KOH per gram: more sulphur in the fuel means more acid on the liner and a larger reserve to neutralise it. The CYN 50 range runs from BN 40 for low-sulphur fuels to BN 100 and BN 140 for high-sulphur residual fuel. What actually reaches the liner is base number multiplied by feed rate, so the two are set together against the engine builder's guidance.
How fuel sulphur sets the base numberWhat happens if the BN is too high for the fuel?
Unused alkaline reserve does not disappear. The calcium detergents that carry it leave ash in the ring grooves and on the piston crown, which can seal the rings and polish or score the liner. On distillate and ultra-low-sulphur fuels the answer is a formulation built for that service, such as CYN 50 BN 40 Cat II ULSFO, not a high-BN oil at a reduced feed rate.
Base number is a budget, not a rankingWhich cylinder oil for VLSFO 0.50% sulphur fuel?
A BN 40 grade is the usual starting point for 0.50% sulphur fuel: CYN 50 BN 40 Cat I, or CYN 50 BN 40 Cat II ULSFO where the engine runs on ultra-low-sulphur or distillate fuel. Both are SAE 50; typical values are in the table above. The final choice follows the engine builder's list and the scrape-down results.
What scrape-down analysis tells youWhich cylinder oil for high-sulphur fuel with a scrubber?
A high base number grade: CYN 50 BN 100 or CYN 50 BN 140. CYN 50 BN 100 is listed in WinGD's Validated Engine Oils, Version 18 (January 2026), covering WinGD X, X-DF, X-DF-A, X-DF-M, RT-flex and RT-flex-DF engines as well as Wärtsilä RTA / RT-flex / X and Sulzer two-stroke engines.
See the validation recordWhat do "5040", "5070" and "50100" mean in marine cylinder oil names?
It is trade shorthand for SAE 50 cylinder oils with a base number of 40, 70 or 100 — our CYN 50 BN 40, CYN 50 BN 70 and CYN 50 BN 100. CYN 50 BN 70 holds Everllence No Objection Letter No. 25975-2026 (Category 1, Group 1, for Everllence B&W two-stroke engines), issued 22 June 2026 and valid to 23 June 2029.
Approval evidence with reference numbers