Originally Posted by mosstrooper
I change mine every 10 years, whether it needs it or not.
Somewhere between mosstrooper and busterwivell is a happy medium. Right now I only have daily drivers (my toys r under construction), but I have changed all my cars/trucks at 5,000 miles for about 15 years now. I used to change at 3,000, (and even 2,000 on things driven hard). But years ago I just decided I was spending too much on oil and filters and came up with a 5,000 mile interval. One logic (for my aging, forgetful brain) was it is easy to remember. I change at even 5s, 25,000, 30,000, 35,000 etc. I never have to write it down anymore, I just glance at the odometer and If it is close (within 500-1000 miles) of an even 5,000 mile increment, I change oil and filter (always both) as soon as is convenient. If I go a few miles over, I don't sweat it. In all these years of doing this, I have never had an internal engine failure I could attribute to lubrication problems (broken valve springs in BB chevy's don't count, that's just the nature of the beast).
As far as a low mileage car goes, there is a greater concern with condensation. I say greater, because condensation can, and does happen in the crankcase of a vehicle that was driven all day one day and sat for all the next day. Once the engine cools off, and air temp and humidity are right (cold metal and high humidity=condensation) there is the potential for the metal to become damp. The difference between occasional driving and daily driving is the daily driver engine is heated up often enough to boil the water out of the oil and off internal engine surfaces before it accumulates enough to affect the lubricity of the oil. In the occasional driver the water can (not always, but can) accumulate enough over time to run down into the oil. Water is heavier than oil, so if it condenses enough to run down the inside of the pan, when it gets to the surface of the oil, it takes a dive to the bottom. Guess where you oil pump pickup is? The result is the water can get "mixed" with the oil, which affects the lubricity of the oil. So how often do I change occasionally driven toys? No more than once a year because I have always driven such cars often enough to feel like condensation was not a problem. Even if I don't drive em, I start 'em up and warm the engine before I shut 'em down. If I start one to just move it out of the way, I always let it run long enough to get warmed up, that boils off any moisture in the crankcase as well as dries out the exhaust system. Once a season, that's too often for me, but it's your money, and more importantly, your peace of mind.
My 2c, and appologies for being so long winded. Now that I have bragged about no engine problems, tomorrow my 75,000 mile pickup (oops, time to change oil!) will probably sling a rod!!