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Hi people - The AD3 152(later 3 cylinder diesel) MF shop manual lists oil pressure 30-60 psi at normal operating speed and temperature, pump relief setting 50-65 psi. The gauges on ours seem to be 80 lb full scale. The earlier A3 152, and the 4 cylinder A4 and AD4 203 are basically the same engines, so the same specs and behaviour seem to apply. The decrease in pressure as the engine heats up occurs from increased bearing clearance, and probably oil pump wear. The decrease starts earlier than in some than others - whether due to my overhaul procedures, or lack of care adding oil (allowing some dirt in, certainly a possibility with loader frames) - I'm not sure. We've had no problems with 40% gauge or better when working. I don't get concerned if I see 10% or more gauge at hot idle. Possibly I should, but, again, it hasn't caused problems so far. We don't generally let them idle for prolonged periods. With the low cost of bearings and oil pump, we generally replace both at overhaul.
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