OTC 5605 Deluxe Compression Tester Kit vs Innova 3612 Compression Tester, 4-piece kit

The 5605 wins on reach and adapter coverage, which is what stops a compression test at the roadside more often than gauge accuracy does. The Innova 3612 costs far less and gets you the same reading on most common engines, so it is the right buy if you only ever test your own car.

OTC 5605 Deluxe Compression Tester Kit

Buy it

The kit that already has the adapter for the awkward engine, on a 26 inch hose you can read from outside the bay.

• The 26 inch flex hose gauge assembly with quick coupler lets you set the gauge somewhere readable instead of squinting into a hot engine bay.
• Adapter coverage is the widest here: an 8 inch deep well 14 mm connector, a 7 inch flex 16 mm Ford Triton adapter, 12 inch flex 14 mm hoses in standard and long reach, plus 10 mm, 12 mm and 18 mm threaded adapters.
• OTC's own instruction sheet ships with the kit and spells out the test procedure and the 10 percent cylinder-to-cylinder limit, so you are not guessing at interpretation.

• It is a big blow-molded case for a job most home mechanics do a handful of times.
• Half the adapters are for engines you may never own, which is most of what you are paying for over the plain 5606 kit.
• The analog dual scale gauge reads 0-300 psi and 0-2100 kPa, so it is not rated for diesel cranking pressures.

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Innova 3612 Compression Tester, 4-piece kit

Buy it

The cheap one that does the job properly, with a side release valve and the clearest instructions of the four.

• A 2-1/2 inch dial with dual-calibrated, colour-coded scales reading to 300 psi, which is easy to read at arm's length.
• The side release valve lets you dump pressure and repeat a cylinder without unthreading the hose, which matters because a repeat test is how you catch a bad seal.
• Innova's operating instructions state the pre-test conditions plainly: fully charged battery, engine at operating temperature, all spark plugs removed, throttle plate secured wide open, and the same number of cranking strokes on every cylinder.

• The hose is 15 inches, so on some engines the gauge sits deeper in the bay than you would like.
• The hose is rubber rather than braided, and the kit is only four pieces: gauge, hose, 12 mm adapter and 14 mm adapter.
• Innova states the tool is designed for spark-ignited gasoline engines not exceeding 250 psi, so it is not a diesel tool.

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Side by side

The bottom line

Our overall pick is the OTC 5605 Deluxe Compression Tester Kit - The kit that already has the adapter for the awkward engine, on a 26 inch hose you can read from outside the bay. Choose the Innova 3612 Compression Tester, 4-piece kit instead if someone testing their own car or light truck who wants a correct answer without buying adapters for engines they will never see.

Want the full picture, including the other options we compared and the popular one we'd skip? Read the complete The Best Engine Compression Testers: 4 Compared (and One to Skip).