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I just had my first service and looked at the oil level. It is not filled up right to the max line shown on the gauge. Is that okay or should it have been filled right to the maximum amount?
I just had my first service and looked at the oil level. It is not filled up right to the max line shown on the gauge. Is that okay or should it have been filled right to the maximum amount?
The reason for the 75% fill recommendation is because the oil heats up and expands while driving, so by the time you're up to temp (or beyond, if on track) that 75% will have expanded to 100%. If you're already at 100% cold, there's nowhere for the oil to go... overfilled.
The reason for the 75% fill recommendation is because the oil heats up and expands while driving, so by the time you're up to temp (or beyond, if on track) that 75% will have expanded to 100%. If you're already at 100% cold, there's nowhere for the oil to go... overfilled.
Right, but the computer won’t even allow a measurement until you’re at full operating temp (not as hot as track use)
The reason for the 75% fill recommendation is because the oil heats up and expands while driving, so by the time you're up to temp (or beyond, if on track) that 75% will have expanded to 100%. If you're already at 100% cold, there's nowhere for the oil to go... overfilled.
No way would sensors read that much of a volume increase by the temperature rise of a liquid; unless the sensor is not linear.
No way would sensors read that much of a volume increase by the temperature rise of a liquid; law of thermodynamics.
I've see it happen on track. Start of a session, oil level reads lower than end of the session. I've also seen it (very clearly) on my analog-gauged 964 on the street. In the 718, it's only 1 liter from bottom to top of the shown range, so each brick is only 250ml. 250ml out of 8L total capacity would only require about 3% volume increase to make the gauge rise by 1 brick.
According to "the internet" (YMMV), the coefficient of expansion of motor oil is 0.00039 per degree F. So if your oil goes from 70 degrees to 220 (i.e. 150 degree change) you'll get a 150*.00039 change = ~.0585. 7.5 liters would become 7.5*1.0585 liters = ~7.9 liters (a 438ml change). With some more math, you'd find that in order to get a 250ml volume increase (one sensor-brick's worth), you'd need 7.5 liters of oil to rise ~85 degrees. For example, 135 to 220 degrees.
Now, if my gauge is reading 3 bricks, but is actually about 3.4 bricks (i.e. not enough to trigger the 4th brick), it would take an even smaller temp increase to trigger that 4th brick. Hence the recommendation to only go to the 3rd brick to avoid overfilling.
Man, I sure hope my math is right.
EDIT: FWIW, I'm also seeing a coefficient of expansion of 0.0007 on the internets, which would almost double my estimates, above - if they're correct in the first place!
I've noticed that the oil level in my car fluctuates by one notch regardless of when I check it, cold or hot engine. I am always able to get a reading in my car so it must be special or it is trying to mess with my brain. Haha. Recently, I noticed the oil level was one notch above minimum and I added ~400 mL of oil in 100 mL increments.
My oil level now fluctuates between full and 3/4ths full cold or hot.
The owner's manual is your friend. Cold oil readings are possible. I always check mine before driving off. And I routinely check my oil when driving and after my drive is done and the car is in the garage.
08-22-2024, 03:42 PM
Oil Change Question
