I will be the first to admit that was a bit wasteful, although I did it whenever I was switching a different car over to GC 0w-30 for the first time and wanted the first UOA to not be mixed in with the previous oil (I wanted to see how well GC held its viscosity in those different applications)
I think it's clever
I don't recall, but I do know that @Patman wouldn't be running an engine with an empty sump and the drain plug out hoping to toss clinging out of the drain hole.
The threads in my Touareg's oil pan are higher than the bottom of the pan, so I get more out via extraction.
Your UOA likely contained 20% of the old oil in the galleries anyway. The "flush" was just for your wallet.
My flush would’ve gotten out a lot more of the old oil than that. What I used to do was drain the oil and then put the plug back on and add 2 liters of new oil. Then I would idle the engine for about 30 seconds and then drain that oil. So after doing that, there was likely less than 5% of whatever oil was previously there before that short flush.
For example on my VQ above - 1.25 quarts stays in. So you add 2 quarts and your ratio is now 62% new and 38% old. You pull your 2 quarts out which is now 38% old so you now have 1.25 - 0.38(2.0) = 0.49 quarts of old left. So I suppose - you removed 3/4 of a quart of the old stuff. I guess if it matters that much.
In some of the engines I put it in they only held 4 quarts of oil (such as my 2000 Civic and my sister’s 99 Civic). In those cases I think that maybe only a half quart of old oil might remain or maybe 13%. But in the case of my 98 Corvette, it might not have been quite as favorable.For example on my VQ above - 1.25 quarts stays in. So you add 2 quarts and your ratio is now 62% new and 38% old. You pull your 2 quarts out which is now 38% old so you now have 1.25 - 0.38(2.0) = 0.49 quarts of old left. So I suppose - you removed 3/4 of a quart of the old stuff. I guess if it matters that much.
Of course I best never hear you telling people a short OCI is a waste of money.
he's just like me frfr.
Who remembers the guy who changed his rental car’s oil?
I remember also. He got many kudos here.
Guilty as charged - I just can't bring myself to leave the filter on for two oil changes. Irrational, but so be it ...I guess it must freak out some folks to keep the filter on for a 2nd OCI and leave a 1/2 quart of “ dirty” oil in the filter and oil galleries. And no, no chance I’ll drain the filter and put it back on.
I looked at a few, mostly Nissan and old Ford's. I would say most are 15-20% range.In some of the engines I put it in they only held 4 quarts of oil (such as my 2000 Civic and my sister’s 99 Civic). In those cases I think that maybe only a half quart of old oil might remain or maybe 13%. But in the case of my 98 Corvette, it might not have been quite as favorable.
It would actually be quite interesting to know approximately what percentage of old oil might remain after a typical 5-10 minute drain on different engines. The oil nerd in me is curious about that
And thankfully I have stopped wasting money like this so I can still scold the diehard 3k people
) and let it suck until it stops. I figure the new oil is going to turn to used oil the first time I drive anyway, so why bother. Puts more obsession back into my OCD bank for something else 
.I felt my ML320 Bluetec got more oil out the dipstick than drain plug. The specified 9 quarts (or was it liters?) filled to just below FULL on the dipstick when drained by suction out the dipstick tube. I was happy.
