What Is a Good Way to Calculate Engine Hours From Miles Driven?

Wide open spaces or bumper-to-bumper; operating conditions play the biggest part in determining engine hours.

Engines, like people, can live many lives in a single incarnation. The same engine that starts out under the hood of a commuter car or pickup truck may someday find itself as the motivator of choice for a generator, boat or even farm equipment. In these applications, having some idea of the engine's total hours of operation can be a good indicator of its value, condition and reliability.

Instructions

1. Look at your city's driving conditions to determine average driving speed. Cars in really congested cities like New York, Boston and Philadephia average around 20 mph; less congested cities like Nashville, Los Angeles and Las Vegas average about 30 mph and really fast cities like Oklahoma City, Kansas City and Tulsa can run upward of 40 mph.

2. Make a fair estimate as to how much city, interstate and rural area driving you do, and assign a percentage to them. For instance, you might estimate you spend about 70 percent of your time in the city, 25 percent out of town and 5 percent on the interstate. Or, you might spend 80 percent of your time in rural areas, 10 percent on the interstate and 10 percent in the city.

3. Multiply your percentages by your car's total mileage. Let's say your car reads 200,000 miles, and you spend 50 percent of your time in the city, 40 percent in rural areas and 10 percent on the interstate. That gives you 100,000 city, 80,000 rural and 20,000 interstate miles.

4. Assign values for each of the three categories. A car will usually average between 65 and 70 mph on the interstate, about 45 to 50 on rural roads and anywhere between 20 and 40 mph in the city, depending upon the city. For this example, we'll assume the car's done its city driving in New York (20 mph), that the driver is conservative on the back-roads (45 mph) and equally so on the highways (65 mph).

5. Divide your mileage for each category by the speed in mph in that category to derive the hours. For this example, we'll divide 100,000 by 20 for the city (equals 5,000), 80,000 by 45 for rural areas (equals 1,777) and 20,000 by 65 for the interstate (equals 308). Add these numbers up to get the total number of estimated hours on the engine. For this example, that comes out to about 7,085 hours.

Tips & Warnings

• This formula doesn't take idle time into account, because it's not a function of mileage; but the average person idles their car about 5 to 10 minutes a day. So, if you want to account for idling, multiply your car's age in years by 365, multiply that by 5 to 10 (depending upon your idling habits) and then divide that by 60 to get the total number of hours spent idling.

References

• Infinite Monkey Corps: How Fast is Your City?
• Consumer Energy Center: Should I Shut Off the Motor When I'm Idling in my Car?
• Bureau of Transportation Statistics: Speeds on Rural Interstate Highways Relative to Posting the 40 mph Minimum Speed Limit