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Insight on a Cummins N14

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Old 03-08-2017, 06:29 AM   #46  
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Location: Cummins Technical Center, IN
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Originally Posted by Hvytrkmech View Post
This would have an affect on an HEUI system. Explain how it affects the HPCR.
Help me understand exactly the question, and I'll give it a try.

When fuel is highly pressurized, small orifices are used to control the flow. (The total travel of an ISX injector "pilot valve" is ~ 50 microns from full open to full closed). Fuel at high pressure moving through small orifices gets VERY hot from fluid shearing.

I'm pretty sure my earlier post above was rather confusing on this point ^^.

Oil systems have much larger orifices and much less pressure. Such a shearing effect is negligible compared to other factors.

One of those factors is piston cooling nozzle flow. Higher pressure is generally more flow through the nozzle. This would (theoretically) pull more heat from the pistons and into the oil.

But this would be a tiny change in oil temp, barely measurable only under specific conditions.

The upshot is this: higher oil pressure by itself does NOT drive "excessive" oil temperature. It may indicate some other problem, though-- perhaps a restriction in the oil system that is preventing sufficient cooling flow-- that may contribute to higher oil temps. But in that case, the higher temp and higher pressure are two effects of a separate cause. The higher pressure doesn't create excessive temps.

What higher oil pressure does is 1) decrease shear life of oil and 2) reduce fuel economy because the oil pump and water pump are two of the largest parasitic loads on the engine. (obviously, fuel pump is much greater).
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