How do you know when it is time to change your engine oil? Maybe there is a sticker on your door that is visible when you open the door and crane your neck down to waist level. But, you still need to subtract the mileage figure on the sticker from the reading on your odometer. It can work, but it is not a great system.

Step 1: Use the Change Oil Light?

Modern automobiles have a Change Oil light on the instrument display. See the green box. It lights when it is allegedly time to change your oil. But, it is only a computer's guess that it is time to change your oil. Your engine's computer notices the amount of city driving you do in comparison to highway driving and guesses that your oil has reached a certain level of contamination from engine wear, water vapor in the crankcase, acids, and engine blow-by gasses. A truly accurate assessment of your oil's condition would require testing in a laboratory.

The Low Tire Pressure light next to the Change Oil light also does not really know if one tire is low. It makes a secondary measurement that is usually explained by low tire pressure. It compares the number of revolutions each tire makes. If a tire is low, it has a smaller effective diameter and must turn more times per minute to keep up with the fully inflated tire on the opposite side of the car. My Low Tire Pressure light has remained "on" since a mechanic worked on the braking system a couple of years ago.

Step 2: Your Odometer Display

The odometer on modern automobile speedometers is digital. In addition to the total number of miles you have traveled, it can also record the number of miles you have traveled on this trip. I do not use it for that. But, I do use it to keep an indicator of how many miles it has been since my last oil change.

The trip meter shows it has been 2270 miles since my last oil change. The manufacturer of my automobile suggests I change the oil every 7500 miles. When mechanics write about oil changes and engine life, they usually say it is better to change the engine oil around 3000 miles. That means I will try to change my oil in just a little over 700 more miles.

Step 3: Trip Reset/Display Button

Normally, my odometer shows the total number of miles my automobile has traveled. If I press the Trip Reset/Display button once quickly, the odometer display changes to the number of miles this trip, or since my last oil change. Every so often when I am driving I press the button to remind myself of how many more miles I will drive before it is time to change the engine oil and filter.

When I change the oil, one of the last things I do is to press and hold the Trip Reset/Display button. This sets it back to zero. I also try to follow the procedure for making the Change Oil light shut off, if it is on.

Step 4: A Paper Record

I also keep a small notebook in the glove compartment. In it I write the date I changed my oil, the miles on the odometer, and anything else I did or changed. The trip meter alone would help me to change my oil at the desired intervals. The paper record will be helpful when I want to sell the car and a buyer wants to know what regular maintenance I have done.

I still need to remember to look at the miles on my trip meter to make certain I change my oil, but using it to keep a record of miles driven since the last oil change makes it far easier for me to remember.