Doug McAllister/Under the Hood: Fuel mileage mistake identified
Q. I read your article about the guy who had his mileage go up suddenly from 22 to 33 miles per gallon. This happened to me, too. I my case, I accidentally changed the odometer to show kilometers instead of miles. I wonder if this happened to him?
A. The car in the earlier question actually was found to have a sensor problem, so in his case it was not a switch over to kilometers, although I can see how that could happen. You also would be less apt to get a speeding ticket with it set on that mode. I had a client come in the other day because she couldn’t get the passenger side window to go up. It turns out she accidentally pushed the child lockout button, which disables all of the windows other than the driver’s.
The moral of the story is when something happens that doesn’t make sense, do a quick check of all the controls and settings before you bring the car into the shop; it just might save you some time, aggravation and money.
Q. I enjoy your column and learn something new every week. A couple of weeks ago, you mentioned not to have a vehicle emission tested after any work was done that required disconnecting the battery. After service, how many miles do you need to drive, for the computer to accumulate enough data, to be able to be tested?
A. Great question! Most cars will reset their monitors after a couple of days of some mixed highway and around-town driving. It’s not just miles, but a combination of miles and drive cycles that include heating-up and cooling-down time. Every once in a while we run into a stubborn car that won’t run enough monitors, and it can take several weeks.
Depending on the year of the car you can have, it will pass emissions testing if one or two monitors have not run. I believe the 2000 model year and later is the cutoff where it switches to where you can have only one monitor not run. The best way to be sure is to run it by your shop before you go to the state’s emission testing lane and ask the shop to run a quick test to see if the monitors have run. This will only take a few minutes and I believe most shops would check this as a courtesy. If the shop did the work, they should want to know that everything is all set and ask you to come back before you go in for the test. At our shop, we get the test done, too, so that when you pick up your car it is all passed and ready to go.
Q. I got an oil change last month and after driving only 24 miles the oil life monitor went from 100 percent to 99 percent. Is it normal to use 1 percent of oil life after only driving 24 miles? Do you think there is a problem with the oil life monitor?
A. I have never checked the monitor that fast after having the oil changed so I don’t know if that’s normal or not. It does seem like it moved a little fast. At that pace you would be due to change your oil again in 2,400 miles. I would reset it and check it again.
Personally, I wouldn’t go by the oil life monitor in making my oil change decision. Find a mileage interval that makes sense based on the kind of driving you do and stick to that interval. You can make a good decision based on the owners manual and the shop that services your car.
Generally a good interval is going to be somewhere in between 3,000 miles and the interval recommended by the manufacturer. If you are using a pure synthetic oil, the intervals are going to be longer and there are other variables as well. Once you establish a good interval for you and your car, the oil change monitor doesn’t matter. If I have gone 4,000 or 5,000 miles on my oil, I could care less what the monitor says; it’s getting changed even if it says 50 percent.
Ÿ Douglas Automotive is at 312 S. Hager Ave., Barrington, (847) 381-0454, and 7218B Virginia Road, Crystal Lake, (815) 356-0440. For information, visit douglasautomotive.com. Send questions to underthehood@dailyherald.com.