Years ago when I drove a semi, the company scheduled the engine oil changes neither by mileage nor operating hours, but by quantity of fuel used. As I remember (and my memory may be faulty) the engine held five gallons, 20 quarts, of oil. The change interval was something on the order of 3000 gallons of fuel burned, or about 600 gallons of fuel per gallon of conventional non-synthetic 15W-40 oil. Since the units cancel out, the ratio of fuel used to oil used was about 600:1. Calculated that way, work out the oil change intervals for your vehicle and see what the ratio might be. My Tundra has averaged just over 15 mpg; its oil change interval is 5000 miles (specified by Toyota) or an oil change every 330 gallons of fuel. Without going out and looking, I think it uses five quarts of oil, 1.25 gallons. That would make its ratio 264:1. Let's see some others.
Sorry missed this comment. If possible, try and stick to one format for comparisons sake. As mentioned on the first page of this topic, Volvo use 60,000 mile (100,000 km) intervals for thier large trucks, given they do mega miles, im not sure how that equates to fuel used, hours etc. But using your formula (hope I did this right) using UK gallons, my intervals are 18,000, car does 62 MPG average so 290 gallons per 0.65 gallons of oil. Sound right?
Some fuel to oil ratios of some motorcycles, for interest's sake.
1. 2007 Honda Elite 80 scooter. It called for an oil change every 1000 miles. It got 80 mpg, so it would burn 12.5 gallons in an oil change interval. It held about 2/3 quart of oil, so had a fuel to oil ratio of 18.7:1. Two-stroke engines typically run about 50:1, so it actually used more oil than a two-stroke.
2. 2007 Suzuki LS650. Oil change interval 3000 miles; about 55 mpg average, for 54.5 gallons of fuel. It held 2 quarts, .5 gallons, for a ratio of fuel to oil of 109:1.
3. 2009 Yamaha 250 Star. Oil change interval 3000 miles; about 79 mpg; 38 gallons of fuel. Oil quantity 1.5 quarts or .375 gallon. Ratio fuel to oil 101:1.
I wanted to edit my previous, as I made an error. The Elite 80 actually had a fuel to oil ratio of about 75:1. I forgot to convert the oil quantity to gallons instead of quarts. Unfortunately, I waited too long to be able to make the edit.
Comments below are worth reading too. Always makes me laugh the comments that say "I've changed my oil every 3000 miles with 200,000 on the clock and never had a problem" well obviously changing the oil too often isn't bad for the car, its just completely and utterly unnecessary
I was on a motorcycle forum for the LS650 until mine got totalled. Factory recommendation was oil changes about every 3000 miles, no doubt 5000 km rounded. One member claimed to change his oil every 500 miles, which caused me to think he was deranged.
I do not dispute that we (and not just Americans) sometimes change the oil too often, on the "cheap insurance" theory. In the sense that clean oil is a "good thing" oil cannot be changed too often. In the sense that it is not necessary for engine longevity, that it is expensive and perhaps wasteful, too-frequent oil changes are not such a good idea. In fact California fairly recently started a campaign designed to convince motorists to change their oil less often.
The 3000 mile oil change came about decades ago, and was probably an upgrade from a 1000 mile interval. It was probably about right in the days of poorer oils, less precise engines, and leaded gasoline (or high-sulfur diesel). When unleaded gasoline became mandatory in the USA, oil change intervals usually went to about 7500 miles - and spark plug life increased dramatically. But the 3000 mile habit remains, and as pointed out quick-lube places and anywhere else that changes oil perpetuates it because it means more work and income for them. There was even a TV commercial for either an oil or an oil filter - I forget which - with the tag line "You can pay me now, or you can pay me later (for the engine overhaul)."
Personally, I usually change the oil in my vehicles according to the manufacturer's recommended mileage. I tend to ignore the time interval, since multigrade oils pretty much eliminate the need for seasonal changes.
Oh, don't remind me of the seasonal oil changes. When I started driving in the 80's most folks were still on the 10W30 "winter" and 10W40 "summer" schedule. I did it for a while on my Buick, but being a poor college student, I settled on 10W30 year round.
I'm not disputing people sticking to what their manufacturer recommends, after all most of us have to do that with a new car to keep the warranty intact anyway. I stick to my service schedule the same as you guys do, but the difference between 3000 miles/every couple of months, and 20000 miles/once every two years is a huge difference. I think when I get my first oil change done at 18,000 I might get the oil analaysed and see how it's held up.