I have a question about oil analysis.
If you change your oil at 50 hrs once and the next time at 25hrs, do you have to correct the results ? How do you make trends with variable oil change intervals ?
You typically state the number of hrs and age of the sample that you send off; the analysis place applies the needed math.
The ppm numbers (on oil analysis I have had over the years) won’t be corrected for the sample duration – they are just straight ppm of that metal in the oil – but the analysis needs to take account of it. And same with oil added during the interval, which has the effect of refreshing the oil. For example this is my last report
The top line is the sample duration in hours. The short interval in 2019 was due to a cylinder repair and a re-hone.
Lead tends to track the sample age pretty well – it comes from burning 100LL. The rest varies.
What readings do you get if you send them a sample of unused oil straight from the bottle?
Zero for everything?
What about one where you put the oil into the engine and drain it out again a few days later without having run it?
I don’t know of anyone wasting 20 quid plus postage to try that 
Yes it should be zero, I think.
If the oil has been in the engine, it won’t be zero; it will collect some stuff from the bottom of the sump. It is for this sort of reason that I warm up the engine before draining the oil and time 1 minute after opening the drain, before taking the sample.
This time I took the oil to 53hrs airborne time
I am now using just W80, with Camguard, 1 bottle spread over about 14 bottles of oil. Dropped 15W50 completely.
