ANSWER: It's your call. We have a '96 Tahoe in which I've continued to use the red/orange Dexcool. Many dealerships and shops replace Dexcool, which uses an organic carbon-based anti-corrosion package, with conventional green coolant that uses phosphate, silicate or borate anti-corrosion additives.

I don't think it really matters which coolant you choose. Just change it every 50,000 miles to ensure that the anti-corrosion and water-pump lubricant additives aren't "used up."

Q: My father was an automatic transmission man for many years. He used to tell me to always back the car in as often as you can, saying it was easier on the transmission, especially in cold weather. Can you explain?

A: I don't see any technical reason why it would make any difference. I don't think the transmission would care whether you engaged "Drive" or "Reverse" to move the vehicle when cold. The transmission's hydraulic system still has to apply a clutch pack by directing fluid under pressure against a piston. If someone knows a valid reason to engage "Drive" first, I'm all ears!

Q: I own a 2002 Nissan Maxima that's been a trouble-free car. Recently a light on the dash went on: "Service engine soon." Mechanics want about $70 just to check it out. I'm a World War II vet on Social Security. Is this a major problem? Can I live with the light on?

A: Continuing to drive the vehicle with the check-engine light on isn't a good idea. The light indicates that something in the engine management system isn't operating properly. You need to have a shop or auto parts store plug in a scan tool to read any fault codes stored in the system's memory. Many auto parts stores will do this for free. Many faults are very minor and easily fixed; others are not.

Q: I own a 2002 Dodge Dakota. About 95 percent of the time when I open either door, my horn goes off. Sometimes my lights will flash. I ordered the truck new and did not get a security system. Neighbors are starting to get tired of it.

A: Chrysler issued a recall that may apply to your Dakota. Call your dealer and check whether safety recall C35 applies to your specific vehicle. According to my Alldata database, the recall identifies potential chafing of a wiring harness under the dash caused by movement of the clutch pedal that can create symptoms very similar to what you describe.

Q: I have a 2007 GMC Denali. The last couple of times I have had it in to the dealer, they have asked if I want the injectors cleaned. I have refused but wonder if I will have warranty issues down the road. Plus the truck runs great and I do run the off-the-shelf cleaner through it periodically.

A: There is no warranty requirement to clean the fuel injectors. I look at this professional service as preventive maintenance, or if there are driveability issues associated with potentially fouled injectors. Stick with what you're doing unless there's a problem.

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