Original Equipment Parts (OE)
OE parts are parts you would purchase over the counter at a dealership. They will be branded with the car manufacturers logo on but this does not mean the car manufacturer made it. like any popular brand it will come at a premieum.
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Original Equipment Manufacturer Parts (OEM)
These parts are made by the company who supply the car manufacturers with
Aftermarket Parts
Aftermarket parts are manufactured by a company different to the manufacturer of your bus or truck. It comes from a company that bystolic in copying replacement parts for different types of vehicles, not just a single truck or bus make and model. The quality, material, and reliability is questionable making them the cheapest option.
The motor oil and especially the additives also undergo thermal and mechanical degradation, whichreduce the viscosity and reserve alkalinity of the oil. At reduced viscosity, the oil is not as capable of lubricating the engine, thus increasing wear and the chance of overheating. Reserve alkalinity is the ability of the oil to resist the formation of acids. Should the reserve alkalinity decline to zero, those acids form and corrode the engine.