Q: I have a 2009 Honda Civic and regularly change the oil when the Maintenance Minder calculates the remaining oil life as less than 5 percent. I use synthetic oil and was recently told by the oil change shop that it lasts twice as long as conventional oil. Is this true? Considering the Maintenance Minder likely does not take into account that the car is running synthetic oil, am I changing my oil twice as often as needed?

A: Honda service literature specifies using a 5W-20 motor oil and changing it at 10,000-mile intervals under "normal" driving or 5,000-mile intervals under "severe service" conditions. Assuming the Maintenance Minder would indicate less than 5 percent oil "life" remaining as mileage approached 10,000 since the last oil change, you are definitely not changing oil too frequently.

In fact, you're braver than I am! I've never been able to wait 10,000 miles or until the oil service reminder indicates it's time for an oil change — I'm just not comfortable waiting that long. Engine sludge buildup occurs as oil is oxidized over time and mileage. Problems from engine sludge still occur, even with today's engine technology and lubricants.

And you are correct — the Maintenance Monitor doesn't know whether the engine is filled with conventional or synthetic lubricant. Nor does Honda differentiate between the two types of lubricants in terms of oil change intervals.

My personal feeling is that you're actually changing oil roughly half as frequently as you should. I use 5,000 miles as my guide for oil and filter changes — more frequent oil change intervals are cheap insurance for your vehicle. And remember, it absolutely is your vehicle and you, not Honda nor the oil change shop, are responsible for any repairs it may need.

Q: I own a 2012 Jeep Grand Cherokee with a 5.7 hemi engine. During ECON mode with Econ light on I hear a clicking noise until I accelerate and the noise goes away and ECON light goes off. This noise seems to be getting louder and other people notice it. No codes come up and it seems to run OK. Is it normal for engines with MDS to make clicking noises and get louder as they get older, or is this a problem developing?

A: As I described in last week's column, engines that utilize some form of cylinder deactivation to improve fuel economy under cruise or low-load conditions do so by disabling valve operation on specific cylinders. GM calls it AFM — Active Fuel Management. Chrysler calls its system MDS for Multiple Displacement System. On your 5.7-liter V-8, the system selectively disables cylinders 1, 4, 6 and 7.

Oil pressure controlled by the MDS solenoids is utilized to deactivate the hydraulic lifters for those cylinders. When the solenoid opens in the ECON mode, oil pressure is applied to a "lost link" pin that collapses the lifter to prevent it from opening its valve. While the lifter is deactivated, a light spring inside the lifter keeps the lifter base in contact with the camshaft lobe while the upper section of the lifter is stationary. There should be no significant noise from operation when the lifters are deactivated.

My best guess is that one of these lifters is at fault. Perhaps there's a problem with the internal spring failing to keep the base in contact with the camshaft, allowing excess clearance in the valvetrain creating the clicking sound. Or perhaps the issue is with one of the MDS solenoids.

Also, be aware that all cylinder deactivation systems are very sensitive to oil viscosity, oil pressure and oil cleanliness. Chrysler recommends 5W-20 motor oil changed at 8,000-mile intervals. See my comments above.

Start with a scan of the powertrain control module to see if there are any oil pressure or P3400-series MDS fault codes. Chrysler's scan tool can test the individual solenoids of the MDS system.

Paul Brand is the author of "How to Repair Your Car" and "How to Repair Your Truck and SUV," published by Motorbooks.