How To Trust Your Mechanic

We've all heard the horror stories; you go to the shop to get your brakes done for $100, and before you know it you've gotten your oil and air filter changed, your transmission flushed, your brake caliper rebuilt, and a bill for way more than what you'd intended.

So how do you know whether or not you need all that stuff?

Picture source: http://www.howto-be.com/how-to-become-a-mechanic/

Owner's Manual
A car owner's best resource is the manufacturer's owners manual. This will help you out when confronted with a service writer or mechanic or manager who is trying to upsell you. Don't get angry at it; it's their job. They may have a policy that says they offer synthetic oil to all customers, regardless of need. You as a car owner need to educate yourself so that when you get that enthusiastic mechanic, you can confidently say, "Thanks, but I'm fine."

There are two concerns with using an owner's manual. The first is driving conditions. Unless you regularly drive your car on the highway or freeway AND minimally use your brake pedal, you are driving under "severe" conditions. This is all city driving, which is what the vast majority of us do. Sometimes an owner's manual will list separate charts for severe versus normal (which really should read optimal, not normal). If you drive under severe conditions, general guidelines for minor maintenance are 3K miles or 3 months for an oil change (you can go longer under certain conditions, like specially formulated oils). Air filters can be replaced once a year; exceptions here would include muddy/dusty driving conditions, etc.

Brakes - I'm going to make a special note here about brakes, because there is a very serious issue with CYA here. A mechanic CANNOT tell you how long your brakes will last, because if they fail before the time he says, he could be (and anedoctally, I've heard has been) held liable. I'll probably throw another post up here with how to look at parts, so when the mechanic says, "Here's why you need new brakes", you won't feel screwed.

The second issue with the owner's manual is that they don't always give you the necessary information. While the owner's manual might tell you that 87 octane fuel is fine and use 10W30 oil, it may not tell you how many quarts of oil your engine will need or what the torque requirement on your tires is.

Good Mechanic vs. Not So Good Mechanic

But what if you're not there for maintenance? How can you tell if she's doing a good job?

Regardless as to the personality of the mechanic, there are steps good mechanics take when they are looking at your car. Most mechanics follow some kind of step-by-step process when diagnosing what's wrong. Usually, these steps include some form of the following, but this list is neither meant to be exhaustive nor applicable to all situations; the mechanic may alter it as necessary:

1) Listening to what's wrong with the car. This is number one. You should not feel comfortable taking your car to a mechanic who listens to three words and then automatically already knows what's wrong, especially if they use terms you don't understand, like EGR valve, ignition timing, or long-term fuel trim. A good mechanic or service writer will be able to explain these things to you in easy terms. If they don't, they're dazzling you with BS (and they aren't likely to know what an EGR valve or long-term fuel trim is themselves).

2) Visual inspection. If listening is number one, this is number two. There are countless stories of this. Customer takes the car in to four different shops, only to find out that the problem was a disconnected spark plug wire. If the mechanic tells you that she knows what is wrong before she even takes a look, your BS detector should go off.

3) Scan data. Assuming the problem hasn't yet been solved, and relates to either engine or transmission issues, the mechanic will probably look at scan data. This is also the likely time for a test drive. A mechanic wants to know what the computer is doing while the issue is occurring. BUT: The computer does not tell the mechanic what exactly is wrong. The computer will list a parameter like this: LTFT +20. The mechanic will have to interpret this data, then figure out what is causing the problem. The computer does not say "Hey, you have a vacuum leak on cylinder 3."

4) Make the repair. You might laugh, but if this wasn't an issue, mechanics wouldn't be the least trusted people along with lawyers and used-car salesmen.

5) Verify the repair. Does no good to fix something if it isn't actually fixed. There is often an issue with what in the industry are called "parts-changers" (I'll say PC here). PCs will look at a problem, come up with something (it's your thermostat!), and replace the part without doing diagnostic testing. 3 months later, you're back at the shop because the thermostat failed again. The PC wasn't "wrong" in replacing the thermostat, especially if it actually wasn't functioning, but he failed to diagnose the underlying issue. Unfortunately, many customers' first experiences with mechanics are like this, and so they tend to distrust all mechanics.

A good mechanic will be open to you if you ask to see the busted part, though understand you may not be able to see the defect (for example, with an old catalytic converter). My favorite mechanics have always been ones who invite me to look under the car with them, but keep in mind at some locations this may be forbidden for insurance purposes (no one wants a customer to get hurt in their garage).

A special note to female customers: Yes, we get yanked around. It's really easy when you have a guy throwing big words at you to get a little confused and just start trusting them and agree. Don't. Ask questions. If you don't understand something, ask them to explain it to you. The more you understand about your car the better an owner you will be and the more money you'll save in the long run.

How Can I Help

Now, as important as it is to be a good mechanic, it will make the process far quicker and easier for all involved if you can be a good customer too.

1) Keep your maintenance records. One possible example: a failed smog can result from an engine rebuild. If the mechanic knows the engine has been rebuilt, it makes it much quicker to diagnose what's wrong than if the mechanic goes in cold without any backstory.

2) Know the context of the issue. What was going on when you had the problem? Were you driving fast, slow? Up hill, downhill? Had you been driving for 10 minutes or 2 hours? While these questions might seem stupid and picky, they reflect the different conditions the computer in your car has to adapt to while you drive. Even something as simple as where you hold the gas pedal when you're on the highway affects what the computer is telling the car to do. Some mechanics will give you a checklist to fill out; another good idea is to write a small story describing what you were doing when the problem occurred.

3) Ask questions. An uninvolved car owner is a car owner who is more likely to come back and frustrate the mechanic. If the good mechanic has told you to do something, ask questions if you don't understand her instructions. The good mechanic knows that if you follow it, you'll cause less headaches for you and her down the road. Which leads me to. . . .

4) Listen to your good mechanic. When you've found that good mechanic, hold on to them for dear life. But also make them want to hold on to you by listening to the advice they give you. This will result in less wear and tear on your car, you, and your good mechanic.