Spark Plug Replacements Should Be at 40k to 60k Miles

December 18, 2010/Steve Tackett


Dear Doctor: I own a 2008 Dodge Charger with the Hemi engine with 18,000 miles on the odometer. I change the oil every five months with synthetic oil and quality filters. The owner’s manual requires that the spark plugs (16) be changed every 30,000 miles or three years. This will cost $500. I know that many cars now have plugs that are good for 100,000 miles. Are these also available for the Hemi? George
Dear George: I do not recommend or believe in the 100,000-mile spark plug replacement. I have seen too many spark plugs rot, blow out, and as well, I’ve seen stripped and torn out heli coils in aluminum cylinder heads. I recommend you replace the spark plugs with the original brand and type every three years in Snow Belt areas or 40,000 miles. Sun Belt areas were rust is not a problem can go five years or 60,000 miles. Always use an anti-seize compound on the tread and die-electric grease on the wires before putting the wire back on the spark plug.
Dear Doctor: I own a 2008 Jeep Grand Cherokee with 14,000 miles on it. Every once in a while my radio stops working while I’m driving. It comes back on randomly. And on one occasion the power windows did not work. The dealer changed the radio, but the problem is still there. Any advice? Arnold
Dear Arnold: Your Jeep, like many other newer vehicles, has multiple control modules to operate accessories. The first step is to check for trouble fault codes in the body control module. This requires a professional scan tool, not a small inexpensive universal scan tool. An updated revised computer software reprogram may be needed. The loss of the power window operation can also indicate a loss of 12-volt power from the ignition switch. The technician will need to check all possibilities. It would be great to have the problem examined when the radio is not working. Unfortunately, there are no easy fixes.
Dear Doctor: I have two problems with my 1993 Honda Civic. First, with the cold weather the trunk gets really wet. How can I prevent this? Secondly, the car is burning too much gas lately. I was getting 30 miles per gallon, but now I’m getting only 24 mpg. Why? Frank
Dear Frank: Water or wetness in the trunk needs to be checked for its port of entry.

jeep grand cherokee

Dampness can sometimes be found under the spare tire in the bottom of the fender wells. A water test can also be performed to locate the source of entry by running water over the rear roof section slowly to see where it may entering the trunk. A loss in gas mileage during cold months is due in part to a change in the gas mixture, the engine running colder, plus lights and heat causing the alternator to work harder. On all fuel-injected engines attention should be paid to the air filter, spark plugs and the oxygen sensor. I also recommend a backpressure test for partly blocked exhaust systems and catalytic converters. The engine temperature is an important part of engine operation. It has to be at 185-plus degrees for optimum performance and economy.
Dear Doctor: I recently had a couple of no-start conditions on my 2002 GMC Envoy. In both cases I moved the gearshift handle from Park to Drive and then back to Park and then the SUV started. On Thanksgiving Day it happened again. Nothing I did would allow it to start. We called a tow to bring it to my mechanic and it started for the tow truck driver. I drove the car to my mechanic and left it with him for a few hours. The condition could not be duplicated and there were no codes in the computer. Can you help? I am afraid to drive anywhere. Cindy
Dear Cindy: Intermittent conditions, such as yours, are sometimes difficult to diagnose. The problem can be anything from the ignition switch, neutral safety switch, starter relay, or starter motor. At my shop we would hook up a test light bulb to the starter motor (S) terminal and position the light so the driver can see the light when starting the vehicle. This will show if there is voltage at the starter when the key is turned. This is where you have to start.
Dear Doctor: You have previously mentioned that it is a good idea when starting a car to turn the key to the “on” position and wait a few seconds before turning the key to “start.” I have mentioned this to several friends who scoff at the suggestion. Your premise sounds logical and I would like to have something in writing for my friends to review. Mike
Dear Mike: There are a couple of reasons for turning the key to the “on” position before actually turning the key to the “start” position. First, when the key is turned to the on position, there is a wake-up call to the battery and computer. And as you may know, battery efficiency decreases as the ambient temperature drops down below 32 degrees. More importantly, the fuel pump primes the fuel system. — Junior Damato, Motor Matters

Junior Damato is an ASE-certified Master Technician.

E-mail questions to

Copyright, Motor Matters, 2010