Can I Use New Tires and a Spare?

John Paul, aka “the Car Doctor,’’ answers readers’ car-related questions.

By John Paul

December 30, 2014

3 minutes to read

Q. I have a 2006 Nissan Pathfinder that has 74,000 miles on it. When I ordered I made sure it had a full size spare tire. I have never used the spare tire and now I need tires. Can I buy three new tires and use the spare?

A. Several car manufactures recommend that tires are replaced if they have been in service for six or more years. The Rubber Manufactures Associations doesn’t look at shelf life but more of how tires are stored. Since the spare was exposed to a variety of weather conditions, if it were my car I would purchase four new tires and keep the spare right where it is.

Q. With cars today, there seems little to do other than change the oil. I have a 2010 Ford F150 pickup and a 2011 Dodge Charger, each with about 35,000 miles. My question is should I have the injectors cleaned, or just buy an additive in a can? My other question is when to flush the transmission and radiator; the dealers all have different recommendations. To me it seems as if these maintenance jobs at the dealers are nothing but a way to produce higher profits and don’t really do anything for the vehicle.

A. All cars have specific maintenance schedules that need to be followed. The vehicles owner’s manual or technical websites like Alldata that I use have this information. Most dealerships and repair shops do a great job of recommending maintenance that will keep your vehicle running trouble free for many years. Although some repair shops will take the scheduled maintenance and add their own suggestions. In some cases these suggestion can be based on known problems that are regional in nature in other cases it may just be about the money. Regarding injector cleaning, injectors can sometimes clog over time and cleaning may help although some manufacturers specifically recommend against it. Transmission and cooling system service can vary as well. Your truck as an example uses doesn’t require coolant or transmission service until well over 100,000 miles.

Q. I recently inherited my grandmother’s 1990 Buick Century and it ran great until I returned for a run on the highway. As I slowed down to make a right turn the car’s engine just stopped. I pulled over and it started right up again, then stalled. I had it towed to a garage, and after four days they could not figure out what was wrong. Fast forward two weeks later – while driving on the highway and making a right turn onto a bridge, my car did the same thing. After I waited a few minutes the car was fine again. At almost 25 years old I don’t want to spend a lot on this car. Any thoughts on this problem?

A. A common issue with some of these General Motors cars was the transmission torque convertor goes into its “lock-up’’ mode but doesn’t release as the car slows down. Have your repair shop look at the transmission; a few simple tests should identify the problem. If the transmission is a three speed (no overdrive), the shop may just unplug the electrical connection to the torque convertor to fix the stalling symptom.

Q. What causes an engine to keep running when it is shut off? The engine is a General Motors 350 cubic inch with a four barrel carburetor in my boat. It does’t always diesel when shut off but sometimes it will. Is there something I can look at over the winter to fix the problem?

A. Engine run-on or dieseling can happen for several reasons. The idle speed could be too high, the engine timing is out of adjustment, the engine could be too hot or the fuel mixture too lean or even excessive carbon buildup in the engine combustion chamber. I would start with checking the basics, such as idle speed and timing and or the winter consider rebuilding the carburetor.