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Do you really need to replace that?

December 4, 2019

You get a call from a mechanic: “Hey, you need a new [insert car part you’ve never heard of]. It’ll cost $781.24. Do you want to repair it?”

For most people, the response is probably “How the heck do I know?”

Does that thing actually need replacement? Is it important? And how do I make sure I’m not overpaying if I do want it replaced?

These questions are stressful. So, we’ve put together a list of three of the most common recommendations you might receive, and how to tell if you need to replace them.

When do I need to replace my air filter?

It is common to replace your cabin filters every 15k – 30k miles this filter is the air you breath in the car. Engine air filters are normally replaced 25k – 40k miles and this is the air filter that goes through the engine. Here are other signs that you may need to replace other vehicle parts.

“Your brakes are low”

If there isn’t enough “friction creating material”, your brakes go “metal to metal”, which is a less safe way of stopping the car and destroys other parts as well.

What the mechanic actually means: When you push the brake pedal, you have brake pads that get pressed against metal discs (“rotors”). The brake pad is lined with friction creating material that wears out over time. Maybe you’re almost out!

What you should ask: Try to get the precise measurement of the brake pads. As a general rule of thumb, if there is less than 3mm of brake pad friction-creating material left, it’s probably fair to replace your brake pads. Most pads start with 10mm-12mm of material. If the mechanic is recommending replacement with more than 3mm of material left, it might be wise to get a second opinion.

Your sanity check: Brake pad replacement depends on the car and the driver. As a general rule of thumb, brakes often come due every 50K miles or so, but there’s a lot of variation there. If you had them changed within the last 10K-20K miles, it might be worth double checking.

What else might be affected? Often, the mechanic will want to replace those metal rotors, too. That’s what the brakes rub up against to stop your car. Some mechanics always recommend replacing the rotors and some recommend every other brake pad change. Sometimes, your existing rotors can be “resurfaced” as well, but most mechanics do not recommend resurfacing rotors more than once.

How much will it run me? It depends on your car (European cars cost more). But, $300-$500 is probably the range that you should expect for front or rear pads and rotors on most cars, nationwide.

“Your engine or cabin air filter is dirty”

What the mechanic actually means: The goal of an air filter is to keep dust and other particles from messing everything up. Over time, if too much stuff has accumulated in the filter, it might restrict airflow and put more stress on the system. This is similar to a house’s air conditioning or heater filter.

What you should ask: Ask the mechanic to see the filter. Keep in mind that there could very well be some dust and dirt on the filter, but that doesn’t necessarily mean it needs to be changed immediately.

Your sanity check: Check your maintenance schedule. Most manufacturers have recommendations on how often you should replace the filters. In certain cases (like you living in a dusty area), you might need to replace the filters more frequently. But usually, it’s 15K-30K miles for cabin filters (filters the air you breath), and 25K-40K for engine air filters (filters the air going into the engine).

What else might be affected? Typically, a moderately dirty engine air filter won’t cause any problems. But if you let the filter get really dirty, it could reduce engine performance and fuel mileage. Similarly, a cabin air filter that’s extremely dirty can hinder the performance of your car’s heating and air conditioning systems.

How much will it run me? It obviously depends on your car, but many mechanics will replace the engine or cabin air filter for $15-$50. Sometimes, it can be more if it’s located in a hard-to-reach spot in the car.

“Your battery is going bad”

What the mechanic actually means: There are a few common reasons we’ve seen:

What you should ask: Batteries typically last 3–5 years, so if it’s more than five years old, replacing it soon is a good proactive step — but the battery might not actually be bad yet. The most scientific test is a “load test”. Ask the mechanic for a load test and what the readings were. If the battery measures less then 9.6 volts during the load test, it should be replaced.

Your sanity check: If it’s been less than 3 years, you either had a bad battery / accidentally drained it, or it might be worth investigating the cause. It’s not impossible, but most batteries should last you 3–5 years. The warranty on the original battery is a good indication of how long it lasts. Batteries always seem to die soon after their warranty ends (what a coincidence).

What else might be affected? In most cases, you shouldn’t need to replace anything else with the battery. However, it’s important to perform the battery load test, because many times, if the car can’t start, it’s not because of the battery at all.

How much will it run me? On most cars, you should expect to pay $125-$200 for the battery replacement, with some differences for battery location. For example, some Mercedes Bens require removing the passenger seat to replace the battery!