GM oil-life monitors use an algorithm

Dear Bob: A year ago I bought a 2004 Pontiac Grand Prix. The vehicle has a printout on the dash telling me when to change the oil. After 8,000 miles, the indicator tells me that I have 30-percent oil life remaining.

This makes me wary; 8,000 miles is a long time on oil, don’t you think? What criteria does this computer use? Shouldn’t cold-weather starts be a factor, along with other considerations?

Sincerely,

— G.H., Independence, Mo.

A: The computers in all General Motors oil-life monitors use an algorithm to determine the correct time to change the oil. Factored into this, as you suggest, are the number of cold starts, the amount of miles driven with a cold or semicold engine, the number of start-stops, the amount of highway driving, the amount of driving in high-heat environments and a number of other factors.

The computer is constantly changing and adjusting the amount of remaining oil life, depending on these factors. Highway driving in warm weather will prod the system to extend your oil-drain interval, while driving in very cold weather and/or stop-and-go traffic will shorten the change interval. The system approximates how much of each of the various protective additives is being used up by various driving conditions, and theoretically will notify you to change the oil before any one of the additives is depleted.

Many car owners are having a hard time adjusting to this system, especially older drivers who have spent decades developing the habit of changing oil every 3,000 miles or so. If in doubt, or if it simply makes you feel better to do so, go ahead and change the oil before the computer tells you to. Remember, you can never hurt the engine by changing the oil too often.

Dear Bob: Hello. I am from Newburg, N.Y., and am an avid reader of your column.

There is a product called Motor Silk being advertised on a local radio station. I am sending you this Web-site address for the product. Can you please give your thoughts on this product?

Thanks.

— W.N., via e-mail

A: I’ve never heard of Motor Silk, but I did check out the Web site.

Seems to me that it’s another product that fits into the solid-lubricant category. It contains boron and, according to the manufacturer, boron bonds to metal surfaces and thus reduces friction between moving engine parts. From what I gather, it is supposed to work something like the various Teflon, molybdenum and graphite additives, in which these respective solid lubricants are bonded in some way to the metal surfaces of the engine.

One thing I did notice: There is no mention of the product having passed any industry-standard tests to back up the manufacturer’s claims of better fuel economy and less engine wear. Until I see tests validating these claims, I would treat the product with caution and skepticism.

I’m certain that the Federal Trade Commission would feel the same way.

Dear Bob: Which system or sensor should I check for the problem of hesitation while driving before the engine is completely warm?

— D.H., Warner Robins, Ga.

A list of sensors that directly affect cold-engine performance, in descending order of their likelihood, would include the coolant-temperature sensor, the temperature sensor/switch, the IAC valve and ISC actuator, the ported vacuum switch, the EGR valve, the throttle-position sensor and the EGR-position sensor.

AMERICAN DRIVERS FIGHT BACK

Here’s a tip that will help you get better gas mileage while fighting terrorism and cutting our nation’s dependence on Mideastern oil:

I’ve noted in the past that the more weight you carry in a vehicle, the less your gas mileage will be. The size of the vehicle and of its engine also play a role in determining how much fuel economy is diminished by adding weight. The fuel economy of a larger car with a bigger engine will be less affected by additional weight than will a smaller car with a smaller engine.

For example: When an extra 100 pounds are added to an 1,800-pound car with a 1.4-liter engine, it will suffer a decrease of about 2.1 mpg. A 5,000-pound vehicle with a 7.0-liter engine will lose only 0.28 mpg when that same extra 100 pounds are added.

Of course, these figures don’t consider the fuel economy of the vehicle before the additional weight was added. While the small car may seem to suffer the most severe penalty from the added weight, its loss of fuel economy is probably fairly close, in percentage terms, to that suffered by the larger car with the larger engine.

Big or little, large engine or small engine, percent loss or actual loss …. Extra weight costs extra money, no matter what nomenclature you use.