Oil analysis procedural question

Not open for further replies.
Oct 7, 2002
Mountain Home AFB, ID
I know how to do an oil analysis from reading the many posts here and from doing them on C-17's. We called em JOAP or SOAP (Joint or Service Oil Analysis Program). Anyway, my question is why do you have to let the oil flow before taking a sample? I'm sure the reply is something along the lines of "to let the settled contaminants out so that we don't get an unusually high reading". Ok, so if this is the case then aren't we still fooling ourselves? This "settled contamination" is still in our oil when the engine runs. It's just suspended from the agitation and flow from the pump. It's still there regardless. By letting it out before we take a sample, yes we are eliminating false high readings in the analysis, but aren't we inadvertantly giving ourselves false lower readings on the materials that fall from suspension? My idea, if the above is true, would be to somehow take a sample while the engine was running. If you had an accessible external oil line, such as for a bypass filter, then couldn't you install a small valve and, once the engine was up to operating temp, open the valve for a sample? Wouldn't this be the most accurate way to get one because everything that is normally in your oil is still there and not just fallen from suspension and then discarded before a sample? I'm no expert but this would seem to make the most sense to me. Any opinions or comments? Thanks! Mikie BTW, I only ask this because I'm coming up on my first analysis on my '00 Excursion with the Oil Guard bypass filter and Amsoil fill.
I think that is still a an accurate way of taking samples, because if you get one large chunk of metal in the oil sample bottle that will throw things off. Generally speaking large particles don't necessarily flow through the engine as they can sit at the bottom of the oil pan. I know the sump on my car doesn't draw oil from the lowest area of the pan. A mid-stream sample is the most accurate represenation of the oil flowing through your engine. Run the engine hot then take the sample in the mid-stream and I think you will be getting an accurate sample of the oil that circulates through your engine the majority of the time.
Mikie Even with a test petcock on your remote filter, I'd let some run out before drawing the sample. You need to be sure that you actually have fresh oil in all the passages of that test connection, and that it is fully flushed of any dirt that might have accumulated in it. Wipe everything off before you test, wipe it with rubbing alcohol, maybe even get into the tight spots with an old toothbrush. Run a few ounces of oil through the test connection into a clean container (OK to put this back into the engine if you had everything clean), then fill your sample jar. Of course, you want your engine fully warmed up before drawing the sample. Ken
I think you see more fuel in the oil at the very beginning of the drain too. In the LS1 long term oil test that has been posted on here, the guy saw 3% fuel in his 1000 mile sample, and he told me he took the sample from the very beginning of the drain (he simply loosened the plug so the oil was dripping slowly and collected it all that way) On his second sample of the same oil, at 2000 miles, he let the oil drain a bit first, then took the sample, and that sample showed only 0.5% fuel. In my own long term extended oil interval test, I figure I'm helping the oil last longer if I drain out about 1/4 of a quart each time I am doing a sample for analysis, this way I'm helping to get more fuel out of the oil. I think I'm going to take my first sample this week or early next week actually, even though I'm only at about 700 miles into the run. I figure it's good to get a baseline on the TBN and viscosity with the oil fairly fresh, and then I can track it's progress from there, taking samples every 3k along the way.
Someone's going to have to explain to me how the timing of the oil sample during a drain relates to fuel dilution. Any fuel dissolved in the oil will be very well distributed. If he had 3% fuel, either he had some sort of external contamination, or that's what was in his entire oil system. If the fuel dilution decreased later, either it evaporated away or the lab did a better job of testing, or some other good reason. Ken
A couple other thoughts I had...first off, I've seen people recommend mostly 10-20 second drain times before collecting a sample. Well, if I tried to do that I might as well do a whole oil change! Seriously. I've timed my drains. From the point where I pull the plug out to the point where the oil is just a trickle is 25-30 seconds on a 6 quart sump! I figure that has to be at least 4 1/2 quarts considering the filter holds 3/4 of a quart. The other thing I thought of was this...even if you take the sample ASAP after turning the engine off, thereby keeping as much crapola in suspension as possible, wouldn't you still be falsifying your analysis because it's not a true representation of what's running in your engine? Also, about the fuel...if I recall, oil is soluble in fuel. The two do not separate, they mix. Therefore, shouldn't the % dilution in a miniscule sample be the same as the whole? I wouldn't think that gasoline would sink to the bottom of oil. In fact, even though I have no valid data to back me up, I'm willing to bet that gas has a lower density than oil, therefore the gas would float atop the oil if the two were not compatible.....which they are! Just some more thoughts! Mikie
No way would I leave the engine running and loosen the drain plug--I drop things. If you have a test petcock on your remote filter assembly, OK, run the engine. If you're loosening your drain plug to let a small amount of oil drain into a sample jar, shut the engine off. The oil in your sump immediately after stopping the engine will be a very good sample. It is important to sample the same way every time. Ken [ December 26, 2002, 01:33 AM: Message edited by: Ken2 ]
Originally posted by Weatherlite: A couple other thoughts I had...first off, I've seen people recommend mostly 10-20 second drain times before collecting a sample. Well, if I tried to do that I might as well do a whole oil change!
In most cases on here though, most people are taking a sample at the very same time that they change out the oil totally. Only a small percentage of people drain out a bit and take samples while still continuing to run the same batch of oil.
I would think if you sample mid-change that extracting through the dipstick tube would be a better option. Not sure if the covers I have for my Miti-Vac would fit the sample jar, but that would seem to be the best solution.
Ken is right it's important to be consistent in the method of sampling. Then trends can be established to look for abnormal wear. Many people change the way they sample on every sample, probably in hopes to get "lower" numbers. I have a fumoto valve so it makes it easier to sample without draining the whole pan. 1) I took the car for a drive bringing it up to operating temperature. 2) About 10 minutes after turning off the engine I used a sterilized 1 qt glass jar and drained 3/4 of a quart into the jar before closing the valve. 3) I then poured from the glass jar into a 4 oz sample bottle. 4) I poured the remaining portion fo the oil back into the vehicle. Based upon the above procedure I'm getting a mixture of the first 15 seconds of oil drain. I will try to stay consistent with this sample method and hopefully will be able to have more statistically accurate samples.
Ok, so for most they do it when they change the oil anyway. Cool. Makes a bit more sense now...I am new to this analysis game so please bear with me. And, for someone who has a remote bypass or even just a remote FF, as long as you have a petcock valve of some sort in the hose line then an engine running test would be optimal as long as I was certain to let the flow go for a couple of seconds to ensure that any contaminants that were in the petcock tube are flushed out. Am I understanding all of this right? I just want to be sure that I am doing this as best as possible. Thanks! Mikie
Forgot one thing...about the crud in suspension in the oil. What is everyone's views about my theory? Do some of the particulates in the oil settle to the bottom? If so, how long do you think it takes for it to do this? I'm asking this because IF it does happen then my idea that the initial "cleansing" drain before taking a sample is indeed getting rid of that stuff...this is the case only if there has been enough time for it to settle. How long does it take you to get the sample after you've turned the car off? If only 2 minutes then I suppose no biggie. BUT, what if you use a lift? You turn it off and then have to actuate the vehicle lift...getting it high enough to at least squat under may take 30 seconds or so but most bring it to full standing height, so figure a minute. Then, you have to go get your drain pan and all of the rags...so maybe 5 minutes on average? What if you're slow? Maybe I'm just playing devil's advocate here but I feel I'm making some valid points that no one seems to be addressing. Mikie
Originally posted by Weatherlite: Forgot one thing...about the crud in suspension in the oil. What is everyone's views about my theory? Do some of the particulates in the oil settle to the bottom? If so, how long do you think it takes for it to do this?
If you've got particles LARGE enough to come out of suspension and settle in the bottom of the pan, your engine has got serious problems--and you don't need an oil analysis to tell you that. [Wink]
Not open for further replies.