An interesting little read for DIYers...
"Do it yourself" jobs you might be better off letting someone else do.
by Eric Peters (2004-02-09)
It's great to save money by changing your own oil and performing other minor service that doesn't require much in the way of special skills, tools, or knowledge. Oil changes are still easy enough to grapple with, even on a $90,000 Mercedes. But as cars have grown in complexity, things that used to be considered "basic repairs" that could be handled by the backyard mechanic are increasingly best left to the pros - even if there's a strong temptation to save some money by attempting them yourself.
An excellent example of this is brake service, which has become much more precision-intensive than it used to be. Unless you have a high-quality torque wrench and know how to use it, damaging expensive parts like brake rotors (and aluminum alloy wheels) by overtightening the lug nuts is remarkably easy to do and very commonly done. People thinking they'd save a couple bucks by installing new brake pads themselves wind up at their dealer complaining about vibrations coming through the steering wheel and other maladies that are frequently caused by having over-torqued the lug nuts and thus warping the $150-a-piece rotors. Ka-ching!
Have you got a dial indicator or micrometer to measure the thickness of those rotors to see if they ought to be replaced? Disc brake rotors used on late model cars often have less material (to save weight) and thus can't be "turned" as often as people are used to. How about a special lathe to "turn" the rotors while they're on the car - as specified by the shop manual and recommended service procedures for many new vehicles? If you don't do it that way or have them "turned" by a local machine shop, off the car, the results may not be good. If the car is equipped with anti-lock brakes, additional considerations will come into play. Do you know how to properly handle all that? If not, leave it alone, unless you like squeaky brakes that might not work right when you need them to.
The fuel system on a modern car is another area where it's often best to leave well enough alone. In the "good old days" carburetors were easy enough to adjust if you followed the instruction in the shop manual and had some basic mechanical aptitude. The idle speed was controlled by a simple screw: in for a faster idle, out to slow it down. Setting the choke was no big deal. And cleaning was even easier, since all it took (short of a complete teardown) was a spray can of carb cleaner. Modern fuel injection systems are not like that at all. They are delicate, complex systems - and easily messed up if you don't know exactly what you're doing. Do you comprehend the functions of the Mass Airflow Sensor? Throttle Position Switch? Idle Air Speed Controller? Cold Start Enrichment Circuit? Can you diagnose each of these components - and isolate a potential problem? If not, resist the urge to start taking things apart as firmly as you would the advances of Anna Nicole Smith. The odds are much greater that you'll make whatever's wrong worse instead of fixing that erratic idle or hesitation problem. Cleaning a modern FI system also requires special power flushing equipment to do it right. And remember, most of these cars have an injector for each cylinder - so eight for a V-8 - as opposed to just the one carburetor used in Ye Goode Olde Days.
Even basic stuff like swapping out spark plugs can be a real challenge on a late model vehicle due to the incredibly cramped confines of the engine compartment. Before you begin pulling off plug wires (if the car even has plug wires; most new cars don't) make sure you'll be able to get them back on again. As for the plugs, don't make the awful mistake of getting one cross-threaded because you couldn't see what you were doing, or the angle was so tight. Few things are as teeth-gritting miserable as having to get a cylinder head Heli-coiled (often requiring its removal from the engine), a job that can cost hundreds of dollars because a $2.99 spark plug was inserted improperly and stripped the threads. If the head is aluminum - common on late-model vehicles - it is especially easy to strip the threads. Also be aware that it's all-too-easy to get grit and grime on the tip of a spark plug that you're fumbling with, trying to find the hole. Now you've pushed debris into that cylinder, which could (and probably will) result in major damage.
The last area of danger it's best to steer clear of is electronics. Twenty years ago wiring harnesses were pretty simple - and even if you toasted one, it didn't necessarily mean the car had become 3000 pounds of ******* lawn art. Today, even improperly jump-starting a late model, computer-controlled vehicle can have absolutely disastrous consequences due to voltage spikes that ruin delicate electronics. So can poking around under the dash, pecking at parts whose function and purpose you can't begin to fathom. If a problem develops, get thee to a dealer - or to a shop with personnel trained and equipped to diagnose and repair what ails thee. Short-circuit the brain box on a new car and finding out the cost to replace it might leave you like Fred Sanford, clutching your chest, awaiting the Big One.
But don't despair. The flip side to all the above is that new cars are for the most part marvels of reliability that, compared to the cars of the past, don't require anywhere near as much hand-holding to keep on keeping on. Remember that before computers and fuel injection came along, it was typically necessary to get at least a minor tune-up (plus, timing and adjust the carb) once a year. Now it's once every three or four, and spark plugs generally go for 30,000 to 50,000 miles. Some don't need to be changed more often than every 100,000 miles. In the past it was once a year or 12,000 miles. No more fussy carburetors that need to be fiddled with every six months, either.
So while you may not be able to do as much yourself as in days gone by, there's less to do and it requires doing less often. That's not a bad trade-off in my book.