vroom vroom!

December 12, 2007 8:46 PM

CarMaintenanceFilter: Do I really need new spark plugs and a fuel-injector cleaning when I just got them done?

April 2006, 67900 miles (10860 km), Mechanic A
I had my spark plugs replaced.

June 2007, 78000 miles (124900 km), Mechanic B
I had my fuel injectors cleaned (with the cleaning compound, using the injector cleaning machine)

Dec 2007, 78200 miles (125133 km), Mechanic C
Regular maintenance, but they tell me that my injectors need cleaning and sparks need to be replaced. When they tell me this, they don't know that I had the work done.

Mechanic A - seems to be reputable and very knowledgeable
Mechanic B - no real proof, but I am giving them the benefit of the doubt that they are honest and skilled as well
Mechanic C - this is the car dealership. Does this make them more honest or reputable? I don't know.

FWIW, I live in a relatively cold climate (winters of -10 Celsius, about 5 F), and have driven rarely in the past year (about 2700 miles, 4300 km). Most of the time, the car sits in the driveway.

So my question is: Did either Mechanic A or B do a shoddy job, is Mechanic C trying to rip me off, or is it "just the way it is", even though I was under the impression that the above-mentioned work would last a whole lot longer than 1.5 years (or 11000 miles) - I am told that sparks should last 25000 miles (40000 km) and injector cleaning should be good for 12000 miles (or 20000 km).

posted by bitteroldman to travel & transportation (12 comments total)

Oh also, I drive a 2000 Daewoo Lanos, 5 speed hatchback, 85 hp, 1.5 L engine
posted by bitteroldman at 8:47 PM on December 12, 2007

I'd guess they're just looking at your odometer, and looking at the appropriate page in the service manual, and then saying "new spark plugs, clean the injectors".
posted by pompomtom at 8:57 PM on December 12, 2007

Yeah, if they don't know it's been done, they're just following a schedule. Nothing seedy, if a bit disingenuous.
posted by TheNewWazoo at 8:57 PM on December 12, 2007

Are they telling you the injectors need to be cleaned because they're dirty? Or are they saying the injectors need to be cleaned because it's the 125k mark and they're just assuming you haven't had them cleaned? They're probably just going down the checklist.

Just tell them "I had my injectors cleaned 200 miles ago, leave them alone." And spark plugs should last about 25-30k miles, yes, so tell them the same about that.

Good on you for replacing them early on your own, btw. Lots of people don't think to. Also:

"Mechanic C - this is the car dealership. Does this make them more honest or reputable?"

Usually less, in my experience.
posted by CrayDrygu at 9:00 PM on December 12, 2007

You don't say whether there are driveability issues with the car (knocking, misfiring, check engine light on, the like). Assuming no one is detecting these issues it's probably (as pointed out above) scheduling. If any of the driveability issues is present they might well be diagnosing a real problem that wasn't solved when the plugs were changed and injectors cleaned.
posted by jet_silver at 9:28 PM on December 12, 2007

Spark plugs do NOT need to be replaced that often unless there is an underlying problem contributing to their effectiveness (fouling, oil, thick carbon buildup, etc). You may want to find out what type of plugs went in, because that'll give you a rough idea of how often you should replace them. I think copper tends to need replacing every 20-30k, while platinum tipped plugs can last 60-100k miles.

Also, fuel injector cleaning is sorta.. well it's a scam (imo). Gasoline is filtered when it pumps into your car at the gas station, and then your fuel filter cleans it as it goes into your engine. If you want, you can go grab a bottle of fuel treatment at Wal-Mart and put some into a full tank. Plenty of people do the bare minimum on their cars (oil changes, necessary parts replacement) and get over 100k miles.

I've always felt that it was useful to "exercise" an engine once in a while. I'll usually go for a 1-hour drive so that I can warm up the engine to full operating temperature, then I'll try to do some hard acceleration to blast out any carbon buildup inside the cylinders. You don't have to go speeding around or anything; just have some fun when the light turns green.
posted by skwillz at 10:38 PM on December 12, 2007

They're just saying it based on mileage. Dealer mechanics are universally less honest, less skilled and more expensive in my experience.
posted by polyglot at 3:45 AM on December 13, 2007

Thanks for the advice thus far. Keep it coming! To answer some of your questions:

I haven't had any driveability issues - the check engine light was on, but that was due to an exhaust valve, which I got replaced.

I took the car in twice recently - the first time for a regular check-up, tire change. At this point, he (the manager) told me about the injector cleaning. And from his tone of voice, it did sound like he was checking my history and saw that it never got done (well, not done at their garage at least).

The second time I took the car in - to change the catalytic converter (still on warranty) - he called and mentioned the injectors again, but also said that one of the mechanics saw that the sparks needed to be replaced. But that's what he told me. Perhaps, he was still reading from the check list or checking my history, and just made up the "the mechanic told me" story, to sound more reputable.
posted by bitteroldman at 7:28 AM on December 13, 2007

Injector cleaning - not a scam at all as a concept. A car that is 70,000 miles old could benefit from it. But it would only need to be done once (assuming it was actually done before). 12,000 miles is not very long for injector cleaning. I would suggest once in the lifetime of the car is enough or every 50,000 miles if you are being super meticulous.

Main dealers go by a manufacturer schedule. The work they do is largely dictated by the schedule that relates to the car - not their own judgment. If the servicing done previously was not done according to a dealer schedule (And they may assume this is the case if the stamps are not 'official') then they will suggest/recommend everything on the manufacturers (mileage denoted) schedule.

So they are not necessarily being underhand, here. Just a little inflexible. Unless they know you've had the work done, in which case they may be trying to wing it/being over zealous. They could, of course, also be being arses. Either way, the work doesn't need doing again.

Also, they (Daewoo) will specify a certain make of plug. If the plug replacement used an equivalent (rather than direct, identical replacement) then to the dealership it 'isn't the right part' and could suggest replacement on that premise alone.

So, tell them the work has been done, and when. If they still try and tell you it needs doing, tell them to poke it. They are clearly trying to con you into doing unnecessary work for the profit potential.
posted by Brockles at 8:02 AM on December 13, 2007

FWIW, Daewoo is now part of General Motors (a division called GMDAT). They make the Chevrolet Aveo (and Optra in Canada), and Suzuki Forenza, Reno & Verona. The closest current product to the Llanos is the Reno I think.

Anyway, they are probably just following the schedule at the dealership. However, that is *not* the schedule you should follow. You should follow the maintenance schedule in your Owner's Manual. Unless there is an objective indication of something else that needs to be done, don't do it; you're throwing money away. When I took my car in for a recent service, the dealer's recommended service was over $300. I went through the list they recommended and compared it with the list in the manual and got everything the manufacturer required done for about $200. Dealerships often pad service packages with services the manufacturer does not require or even suggest on the assumption that their customers trust them, and make a lot of money because the customers never check upon them.

If the dealer says you should get a service done because it is "recommended" but they can't point to an Owner's Manual requirement or a problem that can be objectively demonstrated to you, try answering them by recommending they hop on one foot for the rest of the day; you are just as justified in suggesting they do that as they are to suggest you get unnecessary maintenance.
posted by Doohickie at 11:26 AM on December 13, 2007

10000 miles? Probably worth doing the sparks... not sure about the injectors.
posted by tomw at 2:37 AM on December 14, 2007

Modern spark plugs last MUCH longer than that. 30,000 is the minimum mileage I would expect, and 100,000 miles out of a set of spark plugs is not unheard of. I had a Ford Aspire (another cheaply built Korean car) and I got over 90,000 miles on the original plugs before I got any hint of misfire.
posted by Doohickie at 8:09 AM on December 21, 2007