Who to believe, the car or the dealer?

Wheels: Bruce asks by email:

“I own a Chevrolet truck and the oil life monitor seems to work well because about every 9-10 miles or months, it displays a message for me to have the oil changed. However, my wife’s Lexus ‘service needed’ light or oil change soon seems to come on prematurely after just 4,000 miles. The Lexus dealer says that I do not need service or an oil change so soon. Which one should I listen to? The car or the dealer? Why does the Lexus turn on the service needed light sooner than needed? I feel the car is ‘crying wolf’ too much. Someday there will be a wolf and I will ignore the warnings.”

Halderman: I think the reason for the difference in the warning has to do with how each system works. The Chevrolet truck uses a computer program to estimate when to change the oil. This program monitors the engine temperature and records the number of engine starts and other parameters and deduct “points” form 100 as the engine operates. For example, the computer program could deduct 2 points after a cold weather start but only one point for driving 500 miles mostly at highway speeds. Then when the percentage of oil life reaches 15% , the change oil soon message is displayed. The Lexus however uses just the miles driven and displays the service needed soon message after 5,000 miles — regardless of the engine operating conditions. Maybe the warning message was reset accidentally or to cause the warning message to appear at 4,000 miles instead of 5,000 miles.

About the Author