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A DIY Car Repair, or a Job for an Expert? Five Questions to Ask Before Doing It Yourself

A DIY Car Repair, or a Job for an Expert? Five Questions to Ask Before Doing It Yourself

 

Guest post by retired ASE master technician Mark Gittelman.

It happens to the best of us: We take on a car repair only to find out the hard way that it’s more involved, more time-consuming and more expensive than we thought. Do-it-yourself repairs can be rewarding (and often cost-effective), but there are some jobs that are better left to the pros.

Here are five questions to ask yourself before taking on a weekend repair job.

#1 Is it Worth the Time and Clean-up?

Raise your hand if you can change your car’s oil with your eyes closed? While it’s true that changing oil is relatively routine and easy on most vehicles, that may not be the case with transmission fluid changes, coolant flushes or other tasks that can be messy and tedious. These jobs are among the most affordable tasks to pay a mechanic for, and the time it saves you in clean-up may be well worth it. Weigh the cost of the job against the value of your time.

#2 Could the Diagnosis be Dubious?

Sometimes a defective automotive part is obvious. Let’s use an example of an upper-radiator hose with a pinhole antifreeze leak: The brightly colored stream of engine coolant will point to the problem area, making diagnosis and repair straightforward and the parts and time involved to complete the operation minimal.

However, in many other scenarios, diagnosis can be much harder to make at home. Many automotive systems have become so complex it’s difficult for the average DIY driveway warrior to successfully fix the problem. The expense of parts and the amount of labor involved in replacing those components can make the repair financially risky as well.

Here’s a classic example of a situation where you might want to seek an expert opinion: If your modern fuel injected vehicle won’t start, you might be tempted to replace the fuel pump (although it should be pointed out that removing a fuel tank isn’t fun in the driveway – it can be dangerous, and the replacement parts are pricey). However, the issue could have nothing to do with the fuel tank at all and could instead lie in a clogged fuel filter, a bad fuel-pressure regulator or an electrical issue with the fuel injection system. A mechanic will have the tools necessary to pinpoint a diagnosis more quickly.

#3 Do I Know the Scope of the Fix?

In the example above, removing the fuel tank when the real issue lies in the electrical system can open the door for you to introduce unnecessary errors while you’re taking things apart. Similarly, taking on a repair that takes on a life of its own can mean you end up at the mechanic, spending more than you would have from the start. A mistaken home diagnosis, or a repair job that ends up being out of your scope, can ultimately lead to added expense and frustration.

#4 Do I Have the Special Tools Needed for the Job?

When you look through a factory-issued service manual and dig into the individual repair procedures, they often quote the use of special tools. Every dealership service department has a tool room filled with these required tools. In fact, in the case of an American car manufacturer, this specialized equipment is sent to each franchise operation automatically.

It’s true that in some cases you can find a way around using a tool designed specifically for a given procedure. However, this usually increases the repair time. It can also lead to the possibility of damaging surrounding components.

Take the example of the water pump on a North Star series V-8 engine. The water pump physically locks into a cooling jacket using a specialized socket. When reinstalling the water pump and aluminum water pump cover, you need two different torque wrenches. Now you’ve purchased three tools for one job. Buying two different torque wrenches and a special socket you’ll only use once in a lifetime makes this operation cost-prohibitive.

#5 Do I Need an Automotive Lift?

One of the best arguments for taking your vehicle into a professional auto repair center is when the job requires raising the automobile up on a hoist. Although it might be possible to set the car up on jack stands, you could find the height insufficient to perform the repair.

In some cases, the degree of difficulty increases exponentially when you can’t walk around underneath. Although you might be able to remove a transmission in your driveway, you will find the task difficult.

Research the project thoroughly from start to finish before buying any parts and breaking out your wrenches. While DIY car repairs can be cost-saving (and even fun), consider the implications of the task and whether a pro is more suited for the job.

Mark Gittelman is a retired ASE master technician with more than 30 years of experience. He shares tips on DIY repairs and how to maintain car value as a writer for CARFAX, an online resource for used car buying.

How to Test Engine Compression

How to Test Engine Compression

Testing engine compression in the AMSOIL mechanical lab.

Engine compression = engine power.

A simple equation even we non-engineers can understand. Compression refers to the pressure your engine generates inside the cylinders while it’s running. How much pressure the engine produces and how well it converts that pressure into usable work influence your engine’s efficiency and power.

How it all works and how wear and deposits can erode compression (i.e. horsepower) over time are interesting topics you can read more about here. But today, we’re talking about how to test engine compression.

For this example, I used my 1998 Toyota Corolla. Don’t laugh. I paid cash for it and it runs as smooth as a sewing machine. I also sought the help of Pat Burgraff, one of the techs in our Mechanical Lab. Pat knows his way around an engine.

#1 Ensure the vehicle won’t start when you crank it over

Testing compression requires you to crank the engine several revolutions, and you don’t want it to fire in the process. Remove the fuel-pump and fuel-injection fuses so you’re not dumping gas into the cylinders each time you crank the engine. Then, disconnect the coil packs. Bear in mind the process for your vehicle may be different from the images here.

Disconnect power from the coil packs.

#2 Pull the spark plugs

Label the plug wires so you return them to the correct positions. Otherwise, your vehicle won’t start when you’re done. Thread the compression gauge into a spark plug opening. Take care not to cross-thread it. You can get a compression tester for less than $50 at most auto parts stores.

#3 Crank the engine

Have a helper crank the engine 5-10 times, or until the needle on the compression gauge stops ratcheting up. Note the psi and move to the next cylinder.

Thread the compression gauge into a spark-plug hole.

Crank the engine until the gauge stops ratcheting up.

What’s considered normal compression?

Here’s where things grow murky. “Good” compression depends on the engine. Unfortunately, engines don’t come with their proper compression stamped on the outside. But a good rule of thumb says that each cylinder in a mechanically sound engine should have compression of 130 psi or higher. While I’ve seen some people claim 100 psi is sufficient, the gearheads and other sources I’ve consulted consider that too low.

In addition, you want consistency from one reading to the next. Again, a good rule of thumb is no more than 10 percent variation between any of the cylinders. That’s not to say 15 or 20 percent variation in one cylinder means your engine is junk. But a good, healthy engine should demonstrate minimal variation.

My trusty Corolla nailed the test, making between 165-175 psi in each cylinder.

If one cylinder has low compression, try pouring about a teaspoon of oil into the spark-plug hole and retesting. If compression increases, it’s likely the rings are stuck or worn. The oil acts as a seal and helps close the gap between the rings and the cylinder wall through which the cylinder is losing pressure.

If that doesn’t work, it’s possible the valves or valve seals are worn.

If you suspect stuck rings, try an engine flush designed to clean deposits, such as AMSOIL Engine and Transmission Flush. You can also try a fuel additive that cleans pistons, like AMSOIL P.i.

Word to the wise: you may illuminate your check engine light performing this test, as I did. It went off by itself after driving a few miles, though.