Some thoughts on spark plugs

Advances in technology have lengthened the maintenance intervals for many pieces on our cars. One of those pieces – the one I am writing about today – is the spark plug. All gas engine cars have them.

When I started in the car business, it was common for plugs to need cleaning every year, and replacement by 15,000 miles. As technology improved and engines got cleaner, the plugs started lasting longer. First it was 30,000 miles, then 50,000, 60,000 miles.

Today, many of the new cars we service have 100,000-mile spark plugs installed at the factory. That 100,000-mile rating was derived by installing the plugs in test vehicles, and then driving them hard and fast to pile on the miles. At various intervals the plugs were removed and inspected for wear. After a number of engineering tweaks, Bosch, Beru, NGK, and other spark plug manufacturers came up with a plug that would last the 100,000 miles and still perform acceptably. Based on that, the carmakers established the current change interval for spark plugs.

So the question today is: How often should you change your plugs, if you have a car with the 100,000-mile change interval? Should you follow the manufacturer’s recommendation, or do something else? Why?

The first thing I point out to new clients when we discuss maintenance is that there is a time component to service as well. Spark plugs may hold up fine for 100,000 miles if driven on the highway every day, but short trips and occasional use will wear them out a lot faster. A person who drives 10-12,000 miles per year may not hit 100,000 miles for almost ten years. That’s way to long to leave a set of plugs in the car.

Carmakers recognize that. If you look in most owners manuals you will see a time specification for plugs. They’ll say something like five years or 100,000 miles. I strongly suggest you pay attention to this time limit when considering long-life wear items like spark plugs.

I have read of spark plugs breaking off in the cylinder head when removed after many years. I’ve never experienced that on a five year old car, but there may well be parts of the world where corrosion is worse (near the ocean, as an example) and it you live in such a place, you’d be wise to consider that fact and adjust your service intervals accordingly.

When changing plugs, the next decision a motorist faces is what plug to buy. If you are at the dealer, the decision is simple: you’ll get original equipment plugs. If you’re at a Bosch Car Care Center, you should get the correct Bosch plugs, and if you’re at an independent or chain store, you best find out what they propose to install to be sure you are comfortable.

Thirty years ago, selection of spark plugs was simple. A dozen part numbers would service a majority of the cars on the road. Today many cars have special plugs and it’s important to install the right one. Every parts store has cross-reference catalogs, all of which lead you to believe any “crossover” plug will work. In my experience, that’s often true for older cars but often wrong on newer vehicles. We’ve seen Land Rover, Mercedes, and BMW cars with ignition misfires that were ultimately traced to “supposedly correct” but off-brand spark plugs.

If you have a late model car, be sure you fit the right plugs.

The last point I’d like to address with spark plugs is what happens if you don’t change them in time. As plugs age, the voltage to fire them increases. A plug that needs 20,000 volts to fire when new may need 80,000 by the time it’s used up. If you go beyond that, the voltage may rise to 100,000 volts or higher. This increased voltage puts much greater stress on ignition coils and wires. Premature ignition failure is the usual result of running plugs too long.

Six spark plugs might cost $80 for your BMW or Mercedes. Six spark plugs and six coils (because you waited too long) could cost $700, maybe more. As you can see, changing plugs before the ignition fails makes very good economic sense!

Where did the $39 BMW oil change go?

I grew up thinking of oil changes as inexpensive, quick services. Yet the simplest of services on a late model Mercedes or BMW seems to cost $150 or $200. How come?

The first part of the explanation lies in the oil itself. In recent years the European carmakers have extracted more and more performance from less and less fuel using sophisticated technologies. Anyone who’s compared a 2008 BMW 5-series to a 533 from the mid 1980s can’t help but notice the difference.

The car designers have pushed the limits of engine technology to get today’s performance. That means engines run hotter, and there’s more stress on the internal parts. Engines now contain plastics and exotic metals, which need different kinds of protection. And finally the service intervals are far longer, so the oil in today’s BMW has to last several times as long as the oil we installed 25 years ago.

The result of that change is a much higher performing car that needs far higher performance lubricants than cars of yesterday. And the costs of getting it wrong are high . . . an engine that fails from sludge buildup or other lubrication failure can easily cost over $15,000 to replace.

Important as it is, engine oil or “motor oil” is totally misunderstood by most technicians and consumers. People glance in their owner’s books and see that their car takes 5-30 oil. They don’t even know what 5-30 refers to, so they assume any 5-30 oil will meet their needs. Nothing could be farther from the truth.

In fact, all non-synthetic and most synthetic SAE 5W-30 oil products available in North America fail to provide adequate protection for North American BMW and Mercedes cars that require a 5W-30 viscosity oil.

For example, both Castrol Syntec 5W-30 and Mobil 1 5W-30 both fail to meet BMW minimum requirements. Castrol and Mobil both make products that are suitable for BMW and Mercedes engines but they are not readily available in North America. Even respected brands like Amsoil and Redline fail to offer products that are approved by BMW. In the case of Amsoil and Redline, SOME of their products will serve well but are not technically approved and do have the potential to create problems under certain conditions.

Due to the widespread ignorance of oil service ratings in North America, BMW reduces the minimum requirements for cars sold on this continent. The Genuine BMW 5W-30 oil meets the reduced "LL-98" requirements. LL-98 is the long life oil standard that BMW established in 1998. That standard was superseded by a tougher one in 2001, BMW LL-01. Robison Service and other good BMW specialty shops use the higher grade "LL-01" approved oil for improved protection. These products will improve protection and improve the effectiveness of the BMW oil monitor system.

Mercedes has similar standards for its cars, and for that matter so do Porsche, Volvo, VW, Audi and most other high end carmakers. Ignoring the carmaker requirements is to court disaster. Having said that, I see that very thing happen all the time. People buy inexpensive oils in the mistaken belief that all oil is the same, and they feel good because they saved $50 on an oil service. But what happens when the engine fails and they face a $10,000 repair bill? That’s truly an expensive lesson.

Oil is not the only component of an “oil service.” There is also the filter. At Robison Service we use genuine filters and filters from Bosch and Mann, two of the principal suppliers to European carmakers. These filters cost a bit more, but once again they meet the carmakers requirements. A filter that clogs and causes an expensive failure isn’t much of a savings . . .

Finally, a proper service includes reading and resetting the maintenance system. All late model BMW and Mercedes cars have flexible service computers, where the car keeps track of what’s due and when. You may think the car just needs an oil change, but the maintenance system may be asking for a brake fluid change and new cabin filters too. Once again, there can be serious consequences if the recommended services are ignored.

Dealers and properly equipped independents will have the necessary electronic systems to talk to the car’s service computer. It’s very important to do this, and to scan for faults, because your car’s computer is all that stands between you and a breakdown in many cases. And if you ignore a stored fault (which may be invisible from the dashboard) you may not get any other warning before the car fails.

Finally, a proper service includes a careful visual inspection by a technician that’s familiar with the marquee. You can’t find that anywhere except at a dealer or specialist.

That’s why we don’t call these services oil changes anymore. We call them small services. BMW separates oil service from inspection service. Mercedes Benz A Service is their small service. We do that because they always include an oil change but they often include additional work as dictated by the car or our inspection.