Monitor gives a sense of when to change oil
Q: Does a reading of 50 on my car’s oil service monitor imply the oil’s lubricity has been reduced by half? This number gets fairly low by the time the car is ready for its next oil change. At what point am I risking damage to the engine?
A: The oil service monitor displays the remaining percentage of service life for the oil.
The figure is generated by a system that monitors, among other things, the number of engine starts, rpm, coolant and oil temperature, throttle position and manifold pressure. It computes how hard the oil has been worked and predicts when it’s time to change it. Engine damage is unlikely to occur unless the oil is not changed until long after the oil service system suggests doing so.
The system will predict a significantly longer oil life if you accumulate most of your miles under consistent highway driving conditions as opposed to doing a lot of starting and stopping. And remember, the oil service monitor does not know what type of oil is in the engine.
Regular lubricants are refined from organic crude oil containing randomsized molecules. After refinement, a regular 5W-30 oil would have an average molecular size of a 5W oil. Synthetic lubricants are refined, distilled, purified and chemically rebuilt for total uniformity and molecular size to provide improved lubrication characteristics. All of the molecules in synthetic 5W-30 lubricant are identical. Semi-synthetic oils are just that — typically a blend of 20 percent synthetic and 80 percent organic lubricants.
Q: I have a problem with both key fobs for my 2010 Jeep Grand Cherokee. I live on the west coast of Canada, where we have wet winters, and I keep my Jeep parked outside.
In order to open its doors, I have to click the fobs over and over. I tried replacing the batteries and I also took the vehicle to a local dealership, where they said there was some corrosion in the fobs, which they then cleaned. The problem hasn’t gone away.
Is there a system in the Jeep that should be looked at by technicians?
A: Since the problem occurs when using either key fob, it would seem the fobs aren’t the source of the problem. I searched my automotive database and found a service bulletin (08-010-10) dated May 2010 that suggests reprogramming the wireless ignition module, or WIN, may correct this problem.
This will be covered if the vehicle is still under warranty. If not, you might want to still go ahead and ask the dealership for a goodwill adjustment since they were unsuccessful in previously attempting to solve the problem. No harm in asking.
Q: My 1993 Mercedes 300E (about 140,000 miles) starts normally, but often, when I step on the accelerator, the engine’s rpm barely budges. The problem seems worse in cooler weather. Sometimes, the issue occurs in the middle of an otherwise normal drive — the engine just suddenly reverts to idle speed.
When it occurs on startup, I have to wait several minutes to a half-hour for the issue to correct itself. Any ideas?
A: Given the intermittent nature of the problem, it’s probably an electrical issue. A bit of research turned up several Mercedes service bulletins referring to similar drivability issues. A bad solder joint in the overvoltage protection relay module has been identified as a potential culprit. An updated relay module (000 540 52 45) is available as a replacement.
Other potential causes include a loss of signal from the speed sensor, a damaged protective screen in the mass airflow sensor or a faulty exhaust gas recirculation switchover valve.
Paul Brand, author of “How to Repair Your Car,” is an automotive troubleshooter, driving instructor and former race-car driver. Readers may write to him at: Star Tribune, 425 Portland Ave. S., Minneapolis, Minn., 55488 or via email at paulbrand@startribune.com. Please explain the problem in detail and include a daytime phone number. Because of the volume of mail, we cannot provide personal replies.