FREQUENTLY ASKED QUESTIONS

By GM Canada Goodwrench - Here are some quick references to help you make your driving experience more enjoyable.

How do I know when I really need new tires?

You can't always tell by looking at the tread depth. Sometimes a tire that appears to have significant tread remaining needs to be replaced. So check the treadwear indicators - bald spots that appear at various intervals on the tread. If you see them in three or more places, you need a new tire.

Also, you need a new tire if:

• You can see cord or fabric showing through the tire's rubber
• The tread or sidewall is cracked, cut, or snagged deep enough to show cord or fabric
• The tire has a bump, bulge or split
• The tire has a puncture, cut or other damage that can's be repaired because of the size or location of the damage

Why can't I just use water in my radiator?

Your vehicle's coolant system is set for the proper coolant mix. With plain water, or the wrong mix, your engine could get too hot, but you wouldn't get the "overheated" warning. Your engine could be badly damaged and might even catch fire. Also, too much water in the mix can freeze and crack the engine, radiator, heater core and other parts. Damage resulting from using plain water or the wrong mixture would not be covered by your warranty. See your Owner's Manual for more specific information.

A 50/50 mixture of water and the proper coolant will:

• Give freezing protection down to -37C (-34F)
• Give boiling protection up to 129C (256F)
• Protect against rust and corrosion
• Help maintain the proper engine temperature
• Let the warning lights and gauges work as they should

Why do I have to keep changing the oil if I'm not burning any?

Oil helps protect your vehicle's engine from premature wear by suspending moisture, abrasive dirt, and contaminants until they're broken down by detergents and traped by the oil filter. But over time, even the best oil loses its ability to do the job. That's why regular oil changes are so important. Even if you don't drive many miles, stop-and-go driving and repeated short trips can increase your vehicle's need for an oil change.

What's the best grade of oil?

Oils recommended for your GM vehicle (gasoline engine only) can be identified by looking for the "starburst" symbol, indicating that the oil has been certified by the American Petroleum Institute (API). Do not use any oil that does not carry this symbol. Check your Owner's Manual for the porper viscosity grade. Diesel engines have a different API symbol.

What is octane?

The octane number or octane rating is a measure of the anti-knock properties of gasoline - a higher number indicates a smaller likelihood of knocking. Using a higher-octane fuel than your Owner's Manual calls for is a waste of money. It doesn't produce more power, performance or fuel savings. Follow the Owner's Manual recommendations regarding fuel octane for your vehicle. The only time that higher octane fuels might be necessary is if your vehicle suffers audible engine knock at highway speeds.

I don't smoke, so what's the film buildup on the inside of my windshield?

The film build-up occurs primarily as a result of harmless agents called plasticizers, which are released from the plastic interior parts and condense on glass surfaces. You can celan them off with GM Glass Cleaner, part number 992727.

When I'm just waiting in my car with the engine running, how long of a wait justifies turning the engine off?

Restarting your vehicle's engine uses about as much gas as 30 seconds worth of idling. Therefore, shutting off your vehicle's engine when you'll be at a standstill for more than half a minute will improve your gas mileage and put fewer emissions in the air.

How come they never lubricate the lug nuts on my wheels? Wouldn't that make them easier to take off when I change a tire?

Lug nuts or studs should never be lubricated. While it may make them easier to remove, they could come off while you're driving. If you can't remove them with the equipment in your vehicle, call the GM Roadside Assistance line provided in your Owner's Manual.