UOA sample location.Dipstick or drain plug?

Joined
Jan 12, 2008
Messages
287
Location
Bay City Michigan
Do any of you think that your UOA's can read differently by sampling oil from your oil dipstick tube using a suction pump, or just by draining from the oil pan and catching some "midstream" with an analysis cup?? I just received my UOA kit from blackstone, and read about how they recommend when draining the oil from the pan to capture the "middle of the drain"...I just wonder when sampling from the dipstick tube with a pump(which blackstone also mentions) if the results could differ greatly from the pan drain option?? I am not an engineer, but I will put my two sense in here.....if this "midstream" is important enough for blackstone to mention this, than how in the world could you get an accurate reading using the dipstick method unless the dipstick tube was perfectly positioned so that it drawed the sample from the "middle" of the sump, and not the bottom where all of the gunk collects, OR the top of the oil sump? It almost makes sense to me that when doing a UOA from the pan that you would want an almost "cold" drain and get the "gunk" right off the bat instead of this "midstream" which could differ form UOA to UOA because you cannot perfectly drain this oil the same time EVERY time! I almost want to do a UOA with the SAME vehicle, and oil, but using both methods described, and then compare results. Does this make sense??? -Ponch
 
Joined
Apr 10, 2004
Messages
778
Location
Herndon, VA
I prefer to draw the sample via a suction pump through the dipstick tube. When I do this, I carefully measure the length of the tubing so that when I insert it into the dipstick tube, it goes no deeper than the dipstick itself. I'm confident this avoids pulling the sample from the bottom of the oil pan - probably closer to the "middle" of the collection of oil in the pan. I think this method also makes it easier to be consistent across multiple samples over the lifetime of the vehicle, by making sure the tube goes in to the same depth each time.
 
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