How do you know your oil is broken down?

[Kissfan79]

This may seem like a dumb question....but how do you generally know when your oil is broken down other than when it is black (not that mine gets that way mind you)? Can you tell by the texture when you rub it off of the dipstick and between your fingers? How dark do you let your oil get before changing it? Just curious .Jim

[engine1]

Just to be clear your oil is not breaking down but the additive package added to the base oil product that is. There are companies that do oil analysis for a fee or if you work somewhere that has a fleet of vehicles that get an analysis done regularly you can usually slip one in on the companies dime! There is really no quick industry accepted tool or test that can determine oils 'effectivness' other than the milage/color indicators. Its not a pH thing like rad fluid or like brake fluid its ability or lack of to absorb water, although it will change a bit to the trained 'finger'; it will move away from your prints quickly when old, just try new ond really old oil and you will get my meaning.

[goodvibe]

Oil will oxidize and thicken over time. It does wear out or we could just filter and replenish the additives. Multiweights tend to thin and then thicken again and continue thickening thereafter. More stable oils may just thicken out of grade. This is also true of synthetic but it takes longer. This will not usually happen within our normal oil change interval. Like engine1 said, the adds get depleted. Usually the acid nuetralizers get used up or the dispersants can no longer keep contaminents in supension. I wouldn't use color as an indicator as some oils get dark quickly because they clean and suspend well but touch can work. There are products that can extend an oils life like Lube Control which has anti-oxidents and dispersants etc. but there's a limit. Basically if your using a good dino, change within 5k mi. or 7500 with synth. to keep the motor relatively clean and happy. After 7500mi. it's a good idea to change the filter anyway so why not just finish the job.