Long Life Spark Plugs don't always last forever

Not too long ago spark plugs were replaced every 30,000 miles.  Then 60k became standard and now it's 100k.  30 years ago spark plugs fouled from deposition.  New engines run cleaner, which means wear has become the limiting factor.

The spark plug manufacturers went to exotic metals to reduce wear, and for the most part those materials work.  However, wear of the carbon steel electrodes is still an issue, and a tired engine can actually foul the exotic metal spark plugs more easily than before, because the exotic metal contact area is smaller.

These images clearly illustrate wear in a modern high performance spark plug, from a car that just arrived for service.  The top photo shows how the electrode wore at an angle, and the top-on view of the plug shows how the deposition pattern (left side only) reflects this pattern.

As the plug wears in a sloped pattern the flame front becomes more and more one-sided which leads to knock and misfires.  The worse it gets the more this particular cylinder's timing will be backed off to compensate, with lower efficiency, more heating, and less power as a result. Uneven plug fouling will raise the necessary firing voltage, which will over stress coil packs.

This particular plug came from a 2009 Range Rover with 80,000 miles.  It's clearly due for replacement even with 20% life remaining by the schedule.  The moral of this story - manufacturer service schedules are a guide, not an absolute.  Some cars will benefit from earlier plug changes.

Remember - as a carmaker their goal is to sell new cars, and part of that plan rides on wearing out the old car while another part rests on low advertised cost of ownership (defer it all till the last possible moment!)

As an owner, your goals may be rather different, especially if you plan to keep your car a long time or pass it on to a friend or family member.

John Elder Robison is the general manager of J E Robison Service Company, independent restoration and Bosch Authorized Car Service specialists in Springfield, Massachusetts.  John is a longtime technical consultant to the Land Rover, Porsche, and Rolls Royce Owner's Clubs, and he’s owned and restored many of these fine vehicles.  Find him online at www.robisonservice.com or in the real world at 413-785-1665

To Maintain or Not to Maintain, that is the question . . .

Lexus service. © copyright JE Robison

“All I’ve done is change the oil, and do whatever service my local garage told me about."  That’s what the owner of a ten-year-old 150,000 mile Lexus told me yesterday.   So what should I do now?

We looked at the receipts and she was right.  A bunch of oil changes, a few sets of tires, a few sets of brakes, and a battery had taken her all that distance.  It hadn’t been very expensive, especially compared to what the dealer wanted when they quoted the recommended services.

Now the car had an engine misfire.  That had caused catalytic converter failure, and a check engine light.  The owner knew the car wouldn’t pass inspection that way, and the corner garage didn’t do work like that.  So . . . the car ended up at our shop.

What does a responsible shop owner do, when someone like that comes in?  It’s like when the CPA has a new client walk in the door and say “I haven’t filed any tax returns since 2003, and now I’ve got this letter.  What do you suggest?”  What indeed.

I have seen some very high mileage Lexus cars in my day.  We had one fellow put 420,000 miles on a 1999 LS400 without a single major failure.  But he did his maintenance.  This car was a bit different.  It was fifty thousand miles past the timing belt change interval, and a hundred thousand past the transmission service date . . . . this car was living on borrowed time.

As I explained to the owner, it costs less than $1,600 to change a timing belt, water pump, and all the stuff in front of the engine.  If the belt breaks the bill is going to be at least $5,000, maybe considerably more.   It’s an all or nothing thing.   Every day you drive without belt breakage, you win.  The day it breaks, you lose big.  No belt lasts forever. 

She decided to change the belt.

We moved on to the other items on the service schedule.  Spark plugs were next.  Why?  Because the car had an intermittent skip.  Ignition failure is the most common cause of misfire faults.  What happens is that the plugs get old.  As they age, it takes more and more voltage to fire them.  That extra voltage puts stress on the wires, connectors and coils, and eventually something fails.  For that reason, whenever you have an ignition miss, step one is spark plug replacement. 

You may still need other parts but you certainly need new plugs if the old ones have been in the car 150,000 miles.

She decided to change the plugs

Now we get to the “other” fluids – brake fluid, transmission fluid, rear axle lube, coolant and power steering fluid.  Some people say, “I went this long without changing them, best leave it alone so I don’t stir things up and cause a problem.”  While many people use that line as a rationalization for doing nothing, it ensures the eventual failure of the system.   Lubricants, like belts and plugs, have a finite lifespan.

Brake fluid absorbs water, and it will rust your brake system from the inside.  Coolant becomes acidic, and dissolves your radiator and engine from within.  Transmission, steering, and axle lubes all pick up tiny metal particles.  Left in the old oil, they will grind away at the bearings till something fails.  At the same time, oil gradually loses its film strength, which is what keeps the gears from galling against each other under load.  

She decided to change the fluids.

In the end, after going through the list line by line, we agreed to do all the deferred service on the car.  It cost a hefty sum, to be sure, but it’s still less than she would have spent had she done it all on time, because some of the things we are doing would have been done several times already.

Which begs the question . . . .

Was the original maintenance schedule too conservative?  If so, she saved quite a bit of money with little or no consequence.  Or will she pay a higher price down the road, as the un-maintained parts and systems fail before their time?

I wish I knew.  I’m sure some carmakers are conservative and others are not.  I’m also sure some drivers are hard on their cars, while others are gentle.

In the past five years I have lost count of the engines I have changed in Mercedes, BMW and other cars because the owners failed to change their oil. I used to ask how they could be so dumb, but after the tenth or twentieth car came in the door I knew the answer.  Cars don’t talk back.  So when money is tight, the car gets neglected.  Most live, but some die.

When I point that fact out, the owners get mad at me.  Fine, I tell them.  I’m not the one making loan payments on two tons of scrap iron because I failed to protect my investment.  That’s the thing about being autistic.   When people act dumb, and machinery suffers, I may take the side of the car and not the human.  Vets feel the same about people who abuse cats and dogs.

The lesson to take away from all this:  You can probably push the maintenance schedules a bit if you drive gently.  But when you do, you take a big risk.  Deferring a $1,000 service won’t be so smart, if it costs you a $7,500 engine.   Carmakers make maintenance schedules for a reason.

Most of the time, when we suggest altering a factory schedule, it is to do something more often, not less.  The carmaker, after all, wants a schedule that keeps the car alive long enough to give them happy owners and a good reputation, but not so long that the car never wears out.  We, as repair people, expect to care for things and have them last almost forever.

So I guess you pick your philosophy, and with it, your repair shop.