Another good way is when you check your oil and see how dark it is. The darker it is the more it has gotten contaminates in it and has started breaking down.
Intuitively perhaps; in reality not so.
Example: The conventional 30 weight motor oil in the engines of my air cooled VW's would turn very dark within 500 miles. Laboratory testing by Blackstone Laboratories revealed that even at 3,000 miles (the recommended change interval) and almost black in color the oil had lost none of its lubricating ability, additives were still at acceptable levels, and harmful contaminants were still low. The "black" was harmless soot/carbon held in suspension in the motor oil and lab reports showed the color had no direct correlation to the actual condition of the oil. However, even though Blackstone Labs recommended extending the change interval to 5,000 miles based upon test results at 3,000 miles, since VW used a screen rather than an oil filter in their air cooled engines and the crankcase only held 2.65 qts. I was never comfortable going much past the factory recommended 3,000 miles.
I am a proponent on periodic oil testing for the following reasons: (1) Actual data from the particular engine and motor oil used will reveal the true condition of the oil and provide a rational basis for extending oil change intervals which will save money over the long term; (2) Test results will show concentrations of metals and other materials in the used motor oil which reveal an abnormal condition of the main bearings, seals and other internal parts before a catastrophic failure of those parts; and (3) peace of mind from knowing rather than guessing.
Admittedly a jeep isn't a high mileage vehicle like an 18-wheeler that requires 10-15 quarts for an oil change at a cost of $200+ at a TA, Petro or Flying J truck stop, may have 10,000-15,000 mile factory recommended oil change intervals, and may cover 600,000 miles between engine rebuilds. For those vehicles, periodic tests that reveal oil change intervals can be extended 33% could save thousands of dollars more than the cost of the lab tests in oil cost alone.
I test the oil in each of my vehicles once each year and have calculated that for my daily driver vehicles I save money over the long term by using the test results to establish extended oil change intervals, and for my jeep and other low annual mileage vehicles I at least break even on the testing cost/extended oil change cost/benefit analysis.
BTW - during the same period that I have relied on Blackstone Labs test results to establish extended oil change intervals I have routinely put 250,000-300,000 miles on vehicles without the necessity for major engine work. An '87 Ford diesel pickup I once owned has had its oil regularly tested and just turned over 500,000 miles without an engine overhaul. Perhaps I (and the current owner of that pickup) could have achieved the same results without the lab tests, but I (we) would have been flying blind so to me it was well worth the cost. YMMV.
For those who don't believe testing is worth the cost, here are my
starting points for oil change intervals based upon decades of oil analysis test results for various engines, motor oils and filters:
Conventional motor oil - 5,000 miles (except in air cooled VW engines without oil filters - the change interval for those stays at 3,000 miles)
Synthetic blend motor oil - 5,000-7,500 miles .
Full synthetic motor oil - 7,500-10,000 miles
These intervals can be adjusted up or down depending upon test results, severity of use, length of time the vehicle idles or sits idle, whether vehicle is stored inside or outside, general condition of engine, miles/hours on engine, etc.
I almost never reach the mileage for an oil change in my jeeps (current and past) because I change the oil in my vehicles twice each year regardless of mileage. Full synthetic oil is a waste of money for me and I could probably stick with conventional oil for my jeep. I use Valvoline Maxlife synthetic blend - more for the additive package for higher mileage engines than its extended change interval. Ironically, it often costs less than conventional motor oil. (Pep Boys prices for 5 qt. jug as of 4/15/18 - Valvoline 10w-30 full synthetic $37.99; Valvoline 10w-30 conventional oil $27.99; Valvoline Maxlife 10w-30 synthetic blend $24.98.) Blackstone tells me that I can extend the change interval to 7,500 miles, but based on the miles actually driven in my jeep the twice per year oil changes come at closer to the 5,000 mile baseline.
Happy oil changing.
