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Hey all, I just swapped a used 4jb1 (non-turbo) into an excavator. I want to check if my oil pressure readings are acceptable. I have an analog oil pressure gauge plumbed into the engine. First start of the day with a cold engine and it is about 70psi. Over 15-20 min of use it gradually drops and holds steady at about 20psi. Is this acceptable, or should I look into this? I am running Rotella t4 15w-40 with a carquest/baldwin oil filter. I am in the states so not many mechanics around with experience with these engines.

Thanks,
John
 

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So all the vehicles I have including my Isuzu have this same thing happen, oil is "thick" when cold and then as it runs and gets hot it "thins" out. I will say 20 is a little low. Is this pressure at idle or when you rev it up to engage
 

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20 PSI of oil pressure at idle when warm is acceptable, but a little low. 20 PSI at a higher than idle RPM is probably too low, meaning the oil pump is worn, and or the bearing clearances are excessive, and or dirty oil passages or restrictive oil filter. When you raise the RPM above idle you should see the pressure increase. Generally you want at least 10+ PSI per 1,000 RPM, so at 2500 RPM you should be seeing a minimum of somewhere in the 30+ range. If the oil pressure stays at around 20 above idle you probably will be rebuilding or replacing that engine in the very near future.
 
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