A newly built or rebuilt engine needs something different from its oil during the first hours of operation. Piston rings are still seating against the cylinder walls, fresh components are bedding together and the engine may be subjected to repeated heat cycles, dyno pulls or varying loads before normal service begins.
AMSOIL Break-In Oil is a dedicated engine running in oil formulated specifically for this stage, providing high levels of anti-wear protection while allowing the controlled friction needed for piston rings to seat properly.
Why Not Just Use Ordinary Mineral Oil?
Using ordinary mineral oil when running in an engine is a long-standing practice, but the important consideration is not simply whether the base oil is mineral or synthetic. The additive package, viscosity and intended purpose of the oil are what matter.
A dedicated running in oil is formulated around the needs of a freshly built engine, rather than the long service intervals, deposit control and fuel economy requirements expected from a normal passenger-car engine oil.
Why Piston Ring Seating Matters
During the initial running in period, piston rings need to establish an effective seal against the cylinder walls. This controlled bedding-in process helps the engine achieve good compression, minimise blow-by and control oil consumption once running in is complete.
Protection During Initial Operation
A freshly built engine can experience high loads during its first start, dyno session and early running period. A dedicated running in oil provides anti-wear protection for camshafts, lifters, bearings and other critical components while the engine begins operating under real load.
It is especially relevant to performance engines, racing engines and rebuilt engines where clearances, materials and operating conditions may differ significantly from a standard production engine.
What About Deposits?
The running in period is temporary. Once the engine has completed the builder's recommended procedure, the running in oil should be replaced with the lubricant suited to the finished engine and its intended use.
Follow the Engine Builder's Running In Procedure
There is no single running in procedure that suits every engine. Follow the recommendations of the engine builder or component manufacturer for initial startup, engine speed, load, dyno operation and oil-change interval.
For more information on protecting a new or rebuilt engine, see our Engine Assembly and Running In Guide, covering engine protection, assembly lubrication, running in and final oil selection.
