... when the engine is started again? I came across this PDF a day or two ago (quite possibly linked to by somebody here on BITOG, but I forgot), and on page 6, it describes how particle counts indicate much higher numbers of contaminants in the oil, after a restart. You can see the document here: https://www.hyprofiltration.com/clientuploads/directory/Products/PDFs/FE-PUB/DFE.pdf Now my question is--is this related to oil filters for passenger cars? Or is this something that happens only with filters for other engines? FWIW, I couldn't find any dating information in the text of the file itself, but when I opened the file up in my PDF reader, the file properties said it was created in 2009.