Engine/Transmission (1998.5 - 2002) Low oil pressure

[dennisdw]

Recently I have noticed my oil pressure has seemed to have dropped. Truck has 280k miles. Have an electric gauge with the sender off the oil filter. Most of my driving is at 45 mph in 5th gear and pressure drops to 35 - 40 lbs. At what pressure should I become concerned? As the RPM'S increase over 1500 it increases to a more normal slightly under 50 lb. To stay under the speed limit I would need to run in 4th gear. Any invite will be greatly appreciated.

 

[gtwitch]

This sounds normal to me, engine RPM produces oil pressure up to the relief pressure determined by the spring in the relief valve, and it the engine is only turning 1500 or less in 5th gear that is the oil pressure you get. In my 99 with NV4500 in 5th this is just what happens. As the folks at Cummins will tell you this engine is designed to run at 2500 to 2800 all day long in the industrial or marine applications so don't lug it, RUN it!! Another problem arises in the 5 speed with lugging and this will cause harmonics at around 1700 to 1800 that are known to cause the 5th gear nut to loosen. Lots of reading to be done here at TDR and on the Cummins Forums.

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