Welcome to Goof of the Month! Every month, we ask for stories from our mechanic pals that highlight the need to understand one’s vehicle, how it works and how to maintain it.
This month’s story comes to us again from Paul Kennaley, a mechanic in Sudbury, Ontario, who stresses the importance of giving your engine’s spark plugs some occasional loving, as well as keeping up on other maintenance to prevent spark-plug failure. In this story, the driver learned the importance of periodic maintenance, and was lucky to have avoided engine damage.
The Complaint
This month, Kennaley reports that a client visited the shop with his relatively low-mileage (140,000 km) 2000 Dodge Intrepid, complaining of poor performance, poor fuel mileage, and general discontent with the way the vehicle was running of late.
“When a customer tells us that their vehicle just doesn’t feel like itself lately, we typically go into tune-up mode,” Kennaley says. “If there’s nothing obviously broken, malfunctioning, or failed on the vehicle, usually a fresh air filter, a clean set of fuel injectors, some attention to the ignition system and some new spark plugs will make a big difference. We also like to scan the computer and check on the fuel filter. In many cases, components wear out slowly, and the driver doesn’t notice they’re suffering from reduced performance until things get really bad.”
Today’s new cars can go far beyond 100,000 kilometres before requiring a major tune-up or serious attention. That’s not the case with the 2000 Dodge Intrepid — especially when it comes to spark plugs.
Says Kennaley: “Many a Dodge from this era use a copper core spark plug from the factory, and they don’t last forever. I recommend changing them every 100,000 km at the absolute maximum. Plus, this is an older car, and it’s burning a little bit of oil, which is bad for spark plugs, too.”
The Mechanic
“For years, this customer had been changing his oil and air filter, and that was about it,” Kennaley said. “He’d never had his fuel system cleaned professionally, or had any attention to his ignition system, or a tune-up or check-up of his engine. All of the plugs and wires were original—long overdue for a change. I explained to him that a new set of plugs and wires would be an excellent idea. These, and a freshly cleaned set of fuel injectors, would help his engine run like new again.”
The Diagnosis
Kennaley began installing the new plugs and wires, and discovered two surprises.
First? One of the inner valve-cover gaskets had failed, allowing engine oil to fill the spark-plug tube, which deteriorated the rubber on the spark plug wire boot, compromising the electrical connection vital to proper firing.
“When the tube is filled with oil, the plug wire may not connect properly with the plug, and the electrical current may not flow properly, and the operation of the engine could be compromised,” Kennaley said.
The solution here was to change the valve cover gaskets, which would keep the spark-plug tubes clean and dry. “This is a great example of why even simple maintenance is so important: I might find another issue that needs attention in the process.”
The second surprise was the big one.
Upon removing one of the spark plugs, Kennaley noticed that its electrode, basically a small metal tip at the edge of the plug that the spark ‘jumps’ to, was missing.
“We can tell a lot about how an engine is running by looking at the spark plugs,” Kennaley said. “When an electrode is missing altogether, it’s pretty alarming. This is a serious problem.”
Since the base of the electrode tip remained intact, this particular plug was still firing, though the resulting spark would be far from optimal, not to mention positioned in a non-ideal part of the combustion chamber. Precision spark? Forget it.
Further, the limited contact surface caused by the broken electrode, as well as the dirt and gunk all over the spark plug, meant that this plug may not have been firing on every power stroke, as required. This could cause missing and hesitation, hence the complaint of poor performance.
“There’s no way this engine was running properly,” Kennaley said. “These spark plugs were pretty beat up, filthy, and in bad shape. The spark required by an engine for efficient operation and power is very precise. When the plugs are in this sort of shape, the spark is weak, and doesn’t effectively ignite the fuel the way it was designed to. It’s especially bad when an electrode is missing. That spark plug was ruined.”
The reason the spark plug failed was interesting, too. Kennaley speculates that since the plugs were so far overdue for a change, they had an excessive buildup of gunk caked onto them. This results in ‘hot spots’ on the tips of the plugs, as the gunk buildup absorbs and traps heat against the metal surfaces of the plug.
“When plugs get this dirty and caked, the hot spots that result can weaken the metal in the electrode, causing it to eventually fall off. It’s not uncommon. This is a great reason to change your plugs on time. Maybe not because they’re not working, but because they’ll gunk up, fail, and even fall apart.”
Further, the errant piece of metal electrode could damage internal engine components, including the cylinder walls or valves—though in this case, it seems the customer was lucky, and that the electrode was likely blown harmlessly out of the exhaust.
The Outcome
In this particular case, the outcome was favourable. With new plugs and new ignition system parts, as well as a fresh set of valve cover gaskets, the customer reported that his Intrepid was “running like a top”, and achieving better fuel economy and performance.
Lesson Learned
Staying on top of your regular maintenance is good for a wide range of reasons—including reducing the likelihood of outright failure of components, even small ones, like a spark plug. Though this customer got off easily with some poor performance and excessive fuel use, the detached electrode could have caused serious engine damage, which would have resulted in a much heftier bill than a new set of plugs, wires and gaskets.
