At what temperature is preheating necessary?
That depends on how you define “necessary”. If you refer to your Lycoming or Continental engine operator’s manual you will find that they recommend preheating if your engine is at less than 20 or 30F. But that’s pretty cold in our view. We’ve always said that the closer your engine is to operating temperature when you start it, the happier it will be. That’s because the bearing clearances, piston & ring fit, and oil temp are where they are designed to be. “It is generally accepted that a cold startup is considered to be anything below 60 F. However, an engine at rest is always cold relative to its normal operating temperatures; therefore, the oil is also thick relative to its designed operating viscosity.” Harold Tucker, Director of Technical Information and Training, ConocoPhillips Commercial Lubricants.
