Engine oils | Frontier

What an engine oil does beyond lubricating

The oil film between ring and liner is only one of the jobs, and not the hardest. The oil carries part of the piston's heat down to the sump, holds in suspension the soot that would otherwise settle in the oil ways, neutralises the acids combustion produces, and seals the rings. On a modern engine it has a newer role still: it actuates variable valve timing and, on some designs, tensions the chain — which is where sensitivity to viscosity at operating temperature comes from, not just at cold start. When an oil "fails", the film rarely fails; usually the alkaline reserve or the dispersancy is used up, and the consequence shows as deposits rather than seizure.

Specifications and viscosity grades in common use

The SAE grade (0W-20, 5W-30, 10W-40, 15W-40) describes viscosity only; what protects the engine is the performance specification. On passenger cars the ACEA sequences matter (A3/B4 for engines without a particulate filter, C2/C3/C5 low-SAPS for those with one) together with the manufacturer approval — VW 504 00/507 00, MB 229.51/229.52, BMW Longlife-04, Porsche C30. On heavy-duty diesel the reference is ACEA E6, E7 or E9 and API CK-4 or FA-4, with approvals such as MB 228.51, MAN M 3477/M 3677, Volvo VDS-4.5, Scania LDF-4, Renault RLD-3. Stage V and Tier 4 Final off-road engines require low-SAPS formulations, so that sulphated ash does not clog the particulate filter. Stationary gas engines are a separate family, with their own ash requirements on biogas and landfill gas.

How to choose an engine oil correctly

The order in which you decide matters more than which brand you end up with:

Start from the service book, not from the viscosity grade: the OEM approval is what keeps the warranty, and the SAE grade follows from it, not the other way round.
Check whether the engine has a particulate filter. If it does, the oil has to be low-SAPS — a high-ash oil shortens the filter's life irreversibly.
Choose the drain interval at the same time as the oil: an extended interval is only valid with the approval that permits it and, across a fleet, with periodic analysis.
Do not mix additive families when topping up. If the same product is not to hand, use one carrying exactly the same approval.
On mixed fleets, cut the number of references in the store. Three well-chosen oils cause fewer mistakes than eight perfect ones.