1974 Cat D5 Original CAT Service manual says check engine oil w/engine off, level ground. Dipstick says check oil level with engine at low idle. It makes a significant difference in oil level. Which is correct?
Does the dipstick have markings on only one side (marked Low Idle)..? If so you should check the oil level with the engine running and the oil warm. Many have markings on both sides. One side is "engine stopped - cold oil", the other is "Low idle - warm oil", and the max marks will be at a different level on each side of the stick. The engine stopped markings are generally to confirm only that it is safe to start. This may be opening a can of worms but are you sure the dipstick is the correct one for the machine.?