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This is NOT an ADEQUATE Oil for your Diesel Engine! | Ask The Expert with NIGEL CALDER
17 November 2025 · 3 min · 2K views
What this video covers
Nigel Calder explains how to identify whether an engine oil is suitable for a marine diesel, using the API donut label found on oil containers sold in the US.▶ 0:45 The critical indicator is the letter "C" in the outer rim of the circular label — "C" denotes diesel formulation, while "S" denotes petrol.▶ 0:55 Subsequent letters such as J, K, or L followed by a 4 indicate the specific blend within the diesel category.▶ 1:29 The centre of the donut specifies viscosity: single-weight oils appear as 30W, multi-grades as 15W-40 or similar, and the engine manual determines which weight is required.▶ 1:35 European oils use an equivalent ACEA labelling system with the same C/S distinction.▶ 2:08 If the exact multi-grade is unavailable, any oil carrying the C designation is preferable to none.▶ 1:53 For offshore cruising in regions where fuel has higher sulphur content — common in developing countries — oils specifically formulated for high-sulphur fuel are required.▶ 2:27 The BoatHowTo Marine Diesel Engine Maintenance course covers oil selection and changes in full detail.▶ 3:01 Using a petrol-rated oil in a diesel engine is the core failure the session warns against.▶ 0:25
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