Trunk piston oils for auxiliaries and gensets.
Thirteen grades across SAE 30 and SAE 40, BN 12 to BN 55. In a trunk piston engine one oil does everything — cylinder, piston, bearings and crankcase — so the base number has to carry the whole duty.
Where TPEO belongs on a vessel
On a vessel with a two-stroke crosshead main engine, the trunk piston oil is for the auxiliary engines and generators — not the main engine, which takes a cylinder oil plus a system oil. On smaller vessels with a medium-speed four-stroke main engine, TPEO covers that engine too.
Performance claims: MAN ES and Wärtsilä.
SAE 30 range
Lower viscosity duty and colder operating conditions.
| Product | TBNmgKOH/g | KV 100°CcSt | KV 40°CcSt | VI | Flash°C | Pour°C | Densityg/ml |
|---|---|---|---|---|---|---|---|
| TPEO 30 BN 12 | 12.0 | 11.50 | 106.4 | 95 | 248 | -24 | on request |
| TPEO 30 BN 15 | 15.0 | 11.60 | 106.7 | 96 | 248 | -24 | 0.897 |
| TPEO 30 BN 20 | 20.0 | 11.60 | 106.7 | 96 | 248 | -21 | 0.901 |
| TPEO 30 BN 30 | 30.0 | 11.30 | 101.2 | 98 | 246 | -21 | 0.905 |
| TPEO 30 BN 40 | 40.0 | 11.50 | 101.9 | 100 | 244 | -21 | 0.908 |
| TPEO 30 BN 55 | 55.0 | 11.80 | 105.9 | 100 | 244 | -18 | 0.916 |
SAE 40 range
The most common choice for marine auxiliary engines running on distillate or residual fuel.
| Product | TBNmgKOH/g | KV 100°CcSt | KV 40°CcSt | VI | Flash°C | Pour°C | Densityg/ml |
|---|---|---|---|---|---|---|---|
| TPEO 40 BN 12 | 12.0 | 14.20 | 146.7 | 94 | 250 | -18 | 0.898 |
| TPEO 40 BN 15 | 15.0 | 14.40 | 148.5 | 95 | 250 | -18 | 0.900 |
| TPEO 40 BN 20 | 20.0 | 14.30 | 148.1 | 94 | 250 | -21 | 0.904 |
| TPEO 40 BN 30 | 30.0 | 14.50 | 148.5 | 96 | 250 | -18 | 0.909 |
| TPEO 40 BN 40 | 40.0 | 14.70 | 148.9 | 98 | 250 | -18 | 0.913 |
| TPEO 40 BN 50 | 50.0 | 14.90 | 147.7 | 101 | 254 | -18 | 0.917 |
| TPEO 40 BN 55 | 55.0 | 15.00 | 146.7 | 103 | 258 | -18 | 0.920 |
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 a trunk piston engine?
The layout of four-stroke auxiliary engines and medium-speed main engines: the connecting rod attaches directly to the piston through a gudgeon pin, the piston skirt runs against the liner and the crankcase sits open beneath it. One oil lubricates the liner and the bearings, drains to the sump and circulates again — which is why these engines need a single trunk piston engine oil rather than the separate cylinder and system oils of a crosshead engine.
Trunk piston versus crossheadWhat is TPEO?
Trunk piston engine oil — the single circulating oil of a four-stroke medium-speed engine. Our SINOVA Marine TPEO range is available in SAE 30 and SAE 40 with base numbers from BN 12 to BN 55; typical values from the data sheets are in the tables above.
What do names like "4012", "4030" or "3040" mean?
Trade shorthand: the first two digits are the SAE grade, the rest the base number. "4030" is an SAE 40 oil with BN 30 — our TPEO 40 BN 30; "3040" is SAE 30 with BN 40 — TPEO 30 BN 40.
Which BN should a trunk piston engine oil have for distillate versus residual fuel?
Base number follows fuel sulphur here as in any marine engine, but in a trunk piston engine the same oil also collects combustion products in the sump, so detergency and the change interval are part of the balance. The lower grades in the range (BN 12–20) suit low-sulphur distillate operation; the higher grades (BN 30–55) suit residual fuel. The engine builder's lubricant list is the deciding reference for a given engine.
How fuel sulphur sets the base numberIs marine engine oil different from automotive engine oil?
Yes. Marine trunk piston oils are monograde SAE 30 or SAE 40 oils formulated around residual and low-sulphur marine fuels, with a base number chosen against the fuel's sulphur rather than the multigrade, long-drain chemistry of road engines. They are specified from the engine builder's list, not from a car-oil label.