6 Diagnostic Tools Every DIY’er Needs

Working on cars and trucks is often a mix of necessity and curiosity. The combination of "this needs to be fixed" and "I bet I can fix this" has gotten more than a few people in over their heads due to swiping credit cards and replacing parts that logic says are faulty even when that's not the case. The key to good DIY mechanic work is diagnostics: everything else is just parts replacing.

If you want to save time, money, and frustration while getting your cars back on the road safely there are a handful of tools that will help stack the deck in your favor. Make sure these are in your tool box-and you know how to use them-to ensure your next breakdown will only be with the car and not your mind.

Compression Tester

The darkhorse in the four-stroke cycle is the squeeze that comes before lighting off the air and fuel mixed in the chamber. Compressing the air/fuel mixture increases the power potential, but if your engine is unable to properly compress the mixture the engine won't run properly. Knowing how much squeeze your engine has is a very helpful diagnostic data point as often we don't have the ability to peek inside an engine easily or without a parts bill that may or may not help the initial problem and could potentially create another.

Leak Down Tester

A compression tester will tell you if you are losing the squeeze, but a leak down tester is more likely to tell you where. Using a compressor rather than piston and crankshaft to provide the pressure in the cylinder, we are able to see exactly how much is escaping and also try and get a feel for where. Use a leak down tester to pressurize the cylinder and listen or feel for leaks from the valves by paying close attention to the intake and exhaust tract. Look for bubbles or changes in coolant level to see if the pressure is escaping the head gasket into the cooling system.

Multimeter

Despite having never met someone who enjoys diagnosing electric gremlins, there are a lot of us who do take the time to suss out why the magical pixies using the copper highways of our wiring harnesses are struggling with a traffic jam or road closure.

Electrical issues often are tough to find but rewarding when solved. Understanding your electrical system and using a shop manual to aid in properly testing various components can save hours and hours worth of headaches and weeks of waiting on parts that may or may not fix the problem at hand. If you find electric work is not terrifying, consider grabbing a power probe for additional diagnostic superpowers.

Vacuum gauge

Leaks on the intake side of the engine can cause all kinds of havoc and strange running conditions. Knowing the vacuum in the intake manifold can tell one a lot in terms of engine health. Ask anyone who has set the ignition timing of an engine by using a vacuum gauge. Spikes or other erratic movements in vacuum on a running engine can point to valves that aren't sealing properly, intake leaks, and even clogged vacuum passages inside manifolds.

Infrared thermometer

Locating parts that may be hot that shouldn't be, or vice versa, can be very telling when investigating the condition and health of an engine. I've used an instant read thermometer to diagnose lean-running cylinders and clogged passages in a radiator by looking for cool spots in what should normally be evenly warm. Sometimes just touch is enough, and other times a spritz of water might tell you just as much, but having an accurate measurement can be wonderful for comparison and these termometers have only been getting more affordable in recent history.

OBD Scan Tool

Cars are more connected than ever and even if your fun to drive car is not very connected, your daily driver likely is. Scan tools that use the on board diagnostics ports found under the dashboard on most modern vehicles can be a very efficient way to narrow down where to start doing actual diagnostics and inspection since often times these tools talk in codes that can be awfully vague or mixed considering it's called on board diagnostics. To be fair, every diagnostic tool is only powerful when used and interpreted correctly.