I found this article a while back about over/underreading on the SR20 depending on which way the dipstick is inserted:
f you insert the dipstick in the “other” orientation, it will read low by as much as a quart to a quart and a half, leading to the possibility of over-filling the oil.
when I did it again a week later the reading was higher.
Maybe some water condensation….
You will get a higher reading a week later because the oil in the upper galleries etc takes ages to leak back down. But it should be only a few mm more.
“Always wipe the dipstick”
It does creep up. By itself, or perhaps by movement due to rocking of wings in wind, or pushing it around on the groud?
I did a quick test and can confirm that the dipstick oil level in my IO540-C4D5D goes up by 3mm between landing + 1 day and landing + 3 days. That is quite a lot if you are trying to estimate oil consumption from the dipstick.
I have just repeated the experiment and indeed this is what happens.
Note that, on an IO540, the dipstick is nonlinear, but if the dipstick is showing between 6 and 9 quarts, 1 quart is worth 12mm. So basically the last 1/3 quart takes an extra 2-3 days to run back down into the sump!
One trivial data point: on my IO540-C4, spin-on oil filter, the oil sitting in the filter is worth 4mm on the dipstick i.e. about 1/3 quart. I actually measured this properly.
However, you can’t know how full the oil filter is. The oil can return quickly into the sump or it can stay longer, depending on a lot of factors, including the position of your nose gear strut.
See above posts. I measured the level after the aircraft was standing for a few days.
It also corresponds well with how much oil is known to come out of the filter after it has been removed, for cutting it open.
I posted this because there are many stories online about “1qt” going into the filter, which is patently not the case. It leads to filling to say 10qts when you actually want 9.
The only way the filter could hold 1qt would be if it screwed on with the fitting at the top. Then the entire volume of it would be holding oil.
