quote:Are you saying that a VOA is need every time you add new oil?
It only needs to be done once on a given oil brand and viscosity grade. This establishes your baseline. If someone has already posted a VOA than it saves you the expense from having to do one too.
Then you can compare the wear metals and viscosity levels of the UOA against the VOA to see what's changed.
From the lab's point of view there are a couple of other reasons to send in a sample of new oil. If the lab runs FTIR analysis they need a reference oil. For this test the instrument scans and stores the reference oil then when you send us a sample it is scanned and compared to the new oil. The instrument then measures the chemical changes that have taken place and that's how we know the condition. If the lab has a reference sample on file then it isn't needed, but if we don't have it the results will be wrong so they are not reported.
We also like to see new oils so we can check for contamination. For Cat machines we have certain cleanliness levels that must be met. Bulk oils are frequently severely contaminated but pails, gallons, and even quarts can be contaminated too. By identifying and correcting problems we can reduce operating costs and get longer life.
As others have mentioned it a good idea to know where you oil is at to start with. Some oils have sodium, copper, silicon, and other stuff that can throw us off when we look at the results. If we know what's there it helps prevent wild-goose chases. Many oils also test positive for glycol so that is something we defiantly what to know about.
And last but not least some people are just curious about their oils and like to experiment by using oils with different additive levels. For this it is a good idea to have the VOA, and then take a sample with just a few miles or minutes on the new oil after it is changed. This provides the best baseline since carryover from the previous sample will be known. It's always good to know exactly where you are starting so you can tell exactly how much change took place and be be left wondering how much the old oil is affecting the new oil.