Q: I have a 2001 PT Cruiser with 100,000 miles on it. Would you recommend a spark plug change? Also, I keep hearing that it's not good to warm up your car nowadays. Hey, when it's 20-below I really don't care if it wastes a cup of gas! They say that the oil is much better these days, but is it really OK to jump in your car when it's very cold and take right off?

A: As I mentioned in my last column, there's no harm in allowing your vehicle to warm up a few minutes in extremely cold weather. Besides generating some temperature in the vehicle's fluids and warming the interior a bit, it gives you time to make sure the windshield, side and rear windows are clear of snow and ice before you drive.

Is it harmful to drive the vehicle as soon as it is started in cold weather? No. As you said, today's motor oils are far superior to oils of just a decade earlier. In addition, manufacturing materials and tolerances are far better and more precise. Add the engine management system's capabilities to fine-tune fuel/air mixture and ignition timing as well as limit engine output during the warmup period, and that means the most efficient and least stressful warmup method in all but extreme cold is to start the engine, let the idle stabilize and drop to normal, engage the automatic transmission, let it idle in gear for a moment or two, then drive the vehicle gently as it gets up to temperature.

My ALLDATA database says Chrysler recommends fresh spark plugs in this engine every 30,000 miles. After this many miles, take care in removing the old plugs to avoid stripping the threads in the cylinder head. Install new plugs with anti-seize on the threads.

Q: Typically I change my own oil. Our newest vehicle has 23,000 miles on it and calls for 0W-20 synthetic oil. It's actually less expensive to let the dealer do it than to buy the oil and filter and do it myself. However, on the last two oil changes I've noticed that they seem to overfill it by 1/2 to 3/4 of a quart. What potential harm can come from overfilling?

A: Slightly overfilling the crankcase with oil, as you've described, usually isn't an issue. If the oil level is high enough to cause a problem, the excess oil is usually blown out of the engine through the PCV system, engine seals and gaskets as it seeks its normal oil level.

If the engine is grossly overfilled and the crankshaft whips the oil into a froth as it spins, the aerated oil can cause a loss of oil pressure and lubrication to engine bearings, potentially causing damage.

How can you tell if the engine is grossly overfilled? Fully warm up the engine while monitoring the oil pressure gauge or warning light. Shut the engine off and quickly pull the dipstick to check the oil for evidence of frothing.

Q: I have a 2001 Toyota RAV4 with 68,248 miles. It has started to give out a puff of exhaust smoke when started in the morning. Oil and coolant levels show full and haven't changed. There is no smoke while driving. What could the problem be or is there even a problem?

A: I don't think there is a problem. A slight puff of bluish smoke on starting a 70K mile engine is not uncommon, nor is it harmful. The typical cause is oil that has collected on the valve stems slowly seeping past the valve seals and guides as the car sits overnight. When the engine is first started, this oil is drawn into the combustion chamber with the incoming air/fuel mixture and burned. Having owned and driven high-mileage vehicles for decades, I see this as upper-cylinder lubrication at startup rather than a problem.