| but it is not appropriate for engines with forged pistons. Stock cast pistons have greater dimensional stability over its range of operating temperatures and they will run around 0.001" piston-bore clearance. This helps to control the piston in its travel and makes them far more tolerant of running cold without slop. With forged pistons you have to run significantly greater piston-bore clearances since the forged alloy has a tighter grain structure - it will expand and contract a lot more as temperature fluctuates. This extra slop is hard on the skirts and cylinder walls if you put the engine under load before the pistons have warmed to operating temp and expanded enough to tighten its running tolerances. This is the primary issue with running a motor cold and really only applies to engine with forged pistons. Oil pressure has nothing to do with it - in fact, when the engine is cold, the oil is much thicker and has greater ability to support the radial loads seen between bearing surfaces thus preventing contact. There is more bearing damage that occurs during a hot start than during a cold start for this very reason. High oil pressure due to cold oil is not an issue - that's what the pressure relief valve is for in the oil pump. I've heard people say that if you run a cold motor hard then you will damage it because the cold oil is thicker which reduces flow volume. While this is true, the oil is still cold, thick, and providing more than ample hydrodynamic support at the bearing gap. The issue with warmup is primarily centered around parts reaching their proper dimensions, and namely the pistons themselves. Myself, with the electric fan setup and the ECU configured to trigger the fan relay at 165F, I start her up and let her idle until I hear the fan turn on. Once the fan turns on, I know she's properly warmed up and off I go.
Enthusiasts soon understand each other. --W. Irving.
Are you an enthusiast? If you are out to describe the truth, leave elegance to the
tailor.
Albert Einstein
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