If you instead count the populations of TTs and NA engines, I will make the alarming assumption that there are more TTs than NAs, so both the median and mode would be 4.1. Looking at overall vehicle populations does preclude the aforementioned "4.0" from being the true mean, however.
Karl, put in about 4 litres, then take it for a drive around the block. When you have switched off the engine, let it stand for a few minutes and then check the oil dipstick. If it needs a small amount, top it up and have a good day.
Don't even need to go for a drive, engine running for a few seconds will be enough to establish full engine oil pressure, i.e. your oil filter is full.
As mentioned 3.9 n/a 4.1 T/T, that's whats in the service manual. (I don't own a T/T but the extra .2L for the T/T is for the oil cooler and lines I'm pretty sure, so you don't need to put in 4.1L should just be about the 3.9 also) some oil trays also have line markers on them, so if its already filled to the right amount, you can see how much comes out, and put the same amount back in, but then also as mentioned, run engine for a minute, and check on level ground, and adjust accordingly
When is the last time you successfully checked the engine oil level while the engine was running? While the engine is operating, there is a large amount of oil "in suspension" throughout the crankcase, valve lifters etc. I would dearly love to know what type of measuring device you use to check under those conditions.
