The “every 3,000 miles or every three months” rule is outdated because of advances in both engines and oil. Many car manufacturers have oil change intervals of 7,500 or even 10,000 miles and six or 12 months. Oil change intervals between 5,000 and 7,500 miles are becoming more common, although some manufacturers recommend that driving style and habits also be taken into account. If you drive a new car or your car is under warranty, I wouldn't risk it, as some sensors could malfunction due to a code error.
However, if you drive an old car that doesn't leak and the color of the oil is still yellowish, time doesn't matter, but I would recommend changing it after 2 years, even if the oil is yellow and you've driven less than 5 km. On many newer models, the weight of your car's engine oil is printed on the cover where the oil is added, and it definitely appears in the maintenance section on the back of the owner's manual. Oil is degraded by heat and pressure, and can accumulate harmful particles that need to be removed. The analysis can tell you, among other things, what the current viscosity is (it will usually be slightly lower than that of virgin oil) and can tell you the total base number, which refers to the acidity of the oil and its ability to neutralize by-products.
Each rod has some way of indicating the right oil level, whether it's two holes, the letters L and H (low and high), the words MIN and MAX, or simply a scratched area. Motor Vehicle Maintenance & Repair Stack Exchange is a question and answer site for mechanics and DIYers who own cars, trucks and motorcycles.
