Im glad there are members like you who corrects our mistakes.
Would you also say thicker oil does not increase the pressure? Because I am also under the impression that if it does, and there was this dude called Bernoulli that might have found a negative relationship between a fluid's speed and pressure
Seriously though, I am a mechanical engineer, and I am quite surprised how factually wrong a significant amount of comments on this forum. I used to believe older members with more posts might have been better educated, but I am seeing that there is an echo chamber effect going on with misinformation
Neil deGrasse Tyson's aphorism, "One of the great challenges in life is knowing enough about a subject to think you're right, but not enough to know you're wrong," comes to mind. It applies to oil pressure misconceptions as well.
Static pressure decreases with velocity to conserve total pressure as dynamic pressure rises. Oil pressure sensors, not always at stagnation points, typically measure combined static and dynamic pressure. Most oil pumps are positive displacement and sized to minimize pressure delay and maintain flow at low idle with hot, thin oil—the worst-case scenario due to:
- Thinner oils flowing faster through the engine's effective orifice.
- Increased internal leakage in the pump chamber.
- Lower RPM reducing swept volume rate and pump efficiency.
Consequently, most engines reach oil pump bypass/regulation between 1300–2000 RPM (e.g., Cummins engines by ~1400 RPM). Above this, oil flow and pressure stabilize, as excess flow is diverted by the relief valve to prevent overpressure. Only at very high RPM with thick, cold oil might the bypass become restrictive, allowing pressure to rise. Thicker oil doesn't increase pressure in the typical operating range; it lowers the RPM at which regulation occurs. Thinner oil raises it. Since pressure is regulated, thicker oil reduces parasitic flow through the engine's effective orifice, not increases pressure, except below regulation (e.g., <1400 RPM).
As a mechanical engineer specializing in engines, I’m surprised by how many engineers misunderstand engine specifics. General mechanical knowledge isn’t enough—engines require specialized expertise. I once heard of a colleague with an MSME asking, “What’s a camshaft?” at a company with “engine” in its name. Specialization matters. When exposed to areas outside my lane (like metallurgy) I tend to pay attention as best I can, because I'm surely a student and not a teacher in that context. But to non-engineering friends and family, they think I know a lot about metals. Maybe I do, but only compared to a complete ignoramus. Conversely, I'm the ignoramus compared to a true expert. It's all relative.
The point here is that being an engineer doesn't make one an expert on all things. And there are quite a few people who have expertise far surpassing what many engineers have, partly because it was obtained by a humble desire or fiery passion to learn, unimpeded by a dunning-kruger-like perception of one's own sphere of competence.
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