dirty oil

[84LX89GT]

I've seen brand new cars get dirty oil almost immediately after you start them because you can't get ALL the oil out during an oil change. One way make sure you have very clean oil is to change your oil, start the car and let it run for a few minutes and drain and refill the oil again. This gets quite a bit of the old oil out. I also think the time you change your oil is dependant on the condition of your engine. If the engine burns oil there will be more sludge buildup than one that is fresh. Oil also tends to seperate and turn into sludge faster with older engines that comsume more oil, also carbon builds up faster in older engines. 3,000 is a safe bet for most vehicles, but you can get away with longer oil changes if the oil isn't being burnt or if the filter is still actually filtering (not bypassing) by that time. I don't risk it, i usually go 3,000 miles just because of the fact that your oil may be good for 5,000 miles, but you never get all of the old oil out, plus if extra dirt gets into your engine somehow (crack in airbox, vacuum leak, skip in gasket sealing, etc. etc.) or small pieces of gasket/carbon falls down into the pan it can clog up the filter fairly quickly with relatively "small" amount of debris. This is just my opinion though, based on what i've seen working on cars.