This is common with mechanics working on the clock. They drain the oil, and then put back in the factory specified amount of new oil without bothering to use the sight glass/dipstick to see if the drained amount equaled the factory specified fill amount. Apparently that wastes enough of their valuable time that they don't want to be bothered doing it. Don't have a problem with my ST because I change my own oil on that, but Its been a constant battle for me with my cars. If I don't have the tech write "check level on dipstick" in big letters on the work order, they always overfill it.
This is something I've wondered about, just how critical is the fill level, probably varies from vehicle to vehicle. One theory is it reduces crankcase air volume, which in theory could raise the pressure caused by cylinder blowby, and possibly stress gasket seals. I had a BMW that was continually overfilled by the dealer, the first vehicle I owned that I didn't change my own oil, and that was the only car I owned that had leaky valve cover gaskets, maybe just coincidence. The crankcase is vented, but perhaps its venting capacity is limited, don't know. If you really overfill a lot, then you get crankshaft foaming action, which isn't good either.
I don't understand. How is a sight glass any different than a dipstick? Seems to me the level in the oil pan/crank case is going to change with the oil's temp and how long you allow oil to drain down from the valve cover. The variance will be seen by both a sight glass and a dip stick - and the stick also gives you the same range from high to low that a sight glass with two lines on it has. I would think that both give you the same level of accuracy - or error.
That's how it always was with sportbikes without centerstands. I would crouch down on the right side of the bike, put the right clipon end into the palm of my hand, and then carefully lean the bike vertical so I felt just a little pressure on my palm, and then look at the sightglass.
Wouldn't all of these variables individually or collectively produce exactly the same variances of reading on a dip stick as they influence the volume of the oil and its position in the engine and not the measuring instrument?
Yes, if you're checking the oil at any "warmed up" temperature and at various waiting times.....how hot and how long are the main variables which vary amount of drain-back/sight glass level. Dipstick checks are usually done when cold, which means the machine has been sitting for a few hours, much more repeatable IMHO. E.g., how do you check your 4 wheeled cages..... cold. Given all that, if you are consistent with either method, you should get more repeatable results. So, when I do an oil change, I go for a ride to operating temperature, park the bike on the centerstand for the same period, I know where it should be in the sight glass fairly consistently.
First, since I come from the era when cars normally burned some oil, I check my car's oil routinely - hot and cold. If I do a high speed run for several hours, I will check the oil in my cars at gas stops (as well as before leaving on the trip). I have never seen any meaningful difference between cold and hot oil levels. Same for my ST. I check the oil after changing it (cold after the short run and wait), and also usually at the end of the day on trips. It takes but a second since I usually park the bike on the center stand. So far, I've not seen any diff between hot and cold checks - but the number of times I have done this on the bike is not a statistically significant sampling.
I haven't had to do a screwdriver in two decades... the good days.
I always check my oil level when the engine is cold (in both my bikes and my cars and usually after they have sat over night) and I never see any variance in the sight glass readings. If one always performs dipstick oil checks under the same unvarying conditions and routinely achieves consistent results and then performs sight glass oil checks under widely varying conditions and gets inconsistent results I don't feel that it is reasonable to blame the sight glass for the error- it needs the same fair opportunity to perform well.
