This comment got me thinking. What does happen to the dip stick reading solely as a reult of a major temperature change. As a rough model, I assumed a square steel oil pan, with a horizontal surface area of roughly 6 inches by 8 inches. At 20 degree C (68 F), the depth of oil in the pan would be approximately 7.45 inches. At -40 degrees C (-40 F) the depth of oil in the pan would be 7.18 inches. At +40 degree C (104 F) the depth of oil in the pan would be approximately
7.54 inches. I did figure in the change in the horizontal area of the pan becasue of the temperature change, but it is trival compared to the change in the volume of the oil becasue of the termperature change. Of course the relation ship between the dip stick and pan would also change with temperature, but only slightly. This can be a complicated calucaltion since it could depend on the angle of the dip stick, any material differences etc. In the most trivial case (everything steel and the dip stick perpendicular to the bottom of the pan), the posiiton of the bottom of the dip stick relative to the bottom of the pan would be essentially unchanged (assuming it is nominally almost touching the bottom of the pan).So it seems to me that you cannot ignore the effect of temperature on the measurement of oil level if you are trying to use this method to estimate oil consumption. If you live in a very cold place and check the oil when the engine and oil are dead cold, and then check it again after you have gotten the oil to operating temeprature, but allowed the oil to drain back to the pan, then the level could be over a half an inch higher even though you have not added nor lost any actual oil. I thought this was interesting. Even in a mild climate, the difference between cold oil and hot oil could be significant (over 0.25 inches). No wonder the "normal" range on a dipstick is so wide. I never thought about this when checking the oil in my farm tractors (I have on that holds 20 quarts of oil - and the oil gets very hot). Now I understand why sometimes the oil level seems to go down over night even though the tractor has not moved since I checked it at the end of the previous days work. I always thought it should go up becasue of the slow drain back of oil to the sump. Live and learn.
Ed