Compression testing kits are specialized tool kits that include the tools necessary to measure the compression pressure in each engine cylinder. The kits are primarily used as diagnostic tools to determine the causes of compression loss, such as worn head gaskets, piston rings, or valves.
The primary component of the kit is the compression gauge, which measures the pressure in each cylinder. Typically, the gauge has a dial display with a 0-300 PSI range for gasoline engines or a 0-1,000 PSI range for diesel.
On average, you can expect to pay upwards of $40 for a compression gauge. If you don’t believe the investment is worthwhile, you can look into a loaner compression tester gauge or other rental options. Most people, especially car enthusiasts, feel the investment is minimal and worthwhile.
Beyond the gauge, a compression testing kit includes a hose. The hose connects the gauge to the spark plug hole, which is the way it reads the pressure from the cylinder. With durability in mind, most hose manufacturers use high-pressure rubber to ensure it can withstand the tests.
While you can find compression testing kits that only include the gauge, hose, and possibly one compression fitting, more advanced sets will consist of several adapters. Threaded spark plug adapters are essential to the testing because they provide a secure connection to the cylinder. Depending on your vehicle, spark plugs come in various sizes, from 10mm to 18mm. Having a kit with different-size adapters ensures you can test pressure levels in multiple vehicles.
Beyond spark plug adapters, some kits include spark plug hole extensions. Not all engines have easily accessible spark plugs or components. Some manufacturers recess the spark plugs, making them difficult to reach with a typical gauge and hose. A spark plug hole extension provides a few extra valuable inches to ensure a gauge reaches the area and seals correctly.
Finally, most compression testing kits come with a blow-molded storage case. Made from a rugged and durable plastic, the case offers protection and organization. That said, not all manufacturers see the value in providing molded cases, so your kit may include a storage bag or nothing at all. It is often worth paying extra to receive a case, especially when a kit includes multiple parts.
While not available in every kit, some manufacturers include items like a quick-release coupler. A quick-release coupler allows for fast hose attachment and detachment. Also, some companies may include an air hold quick connector. The attachment allows for valve stem seal replacement without removing the cylinder head.
If your engine shows signs of performance issues, you might want a compression testing kit to determine specific performance problems. That said, it might be best to leave diagnostic testing to the professionals if you are an amateur mechanic or hobbyist. Contact a local mechanic and schedule a vehicle checkup. If you want to test the engine yourself, talk to an experienced representative and your local auto parts dealer about a compression testing kit.
