PROTON Cylinder Gauge (4-in-1 Digital Diagnostic System)
The Proton replaces four separate engine-diagnostic tools with one touchscreen unit — a digital compression tester, a cylinder leak-down tester, a pressure & vacuum gauge, and a top dead center (TDC) assistant. Every reading is logged automatically to the cylinder it came from, and the leak-down percentage is calculated for you the moment you dial in 100 PSI — no notepad, no dividing one analog gauge by another. A single chart screen puts every cylinder side by side so a weak one is obvious at a glance. Built for gasoline engines up to 8 cylinders, with multiple spark-plug adapters and quick-connect fittings included, and backed by a 5-year 100% full-coverage warranty with USA-based replacement.
Best for: independent repair shops and professional technicians running compression and leak-down as part of routine diagnosis; mobile mechanics who need one compact kit instead of four; engine builders and performance shops verifying cylinder sealing; and serious DIY mechanics chasing a misfire, a burnt valve, or a suspected head gasket.
What it diagnoses
- Worn or broken piston rings — low compression plus air escaping into the crankcase.
- Burnt or leaking valves — air escaping out the intake (intake valve) or the exhaust (exhaust valve).
- Blown head gaskets — two adjacent cylinders down together, bubbles in the coolant, or air crossing into the next cylinder.
- Poor cylinder sealing — scored bores, carbon on a valve seat, anything that costs a cylinder its seal.
- Vacuum and timing problems — low or unsteady manifold vacuum, restricted exhaust, and general vacuum leaks.
Four tests, one unit
- Digital compression test — thread the hose into a spark-plug hole, select the cylinder on screen, and crank. The peak reading is captured and logged to that cylinder automatically.
- Cylinder leak-down test — feed the sealed cylinder 100 PSI of shop air and the Proton calculates and displays the leak percentage. Where you hear the air escaping tells you which part failed.
- Pressure & vacuum gauge — read manifold vacuum on a running engine in inHg, kPa or PSI, with high and low modes and a live graph-over-time view that shows whether vacuum is steady or oscillating.
- Top dead center (TDC) assistant — find TDC by watching pressure and vacuum as you turn the crankshaft, instead of guessing with a screwdriver or hunting timing marks. Accurate TDC is what makes a leak-down number mean anything.
Specifications
| Feature | Detail |
|---|---|
| Tests performed | Compression · Cylinder leak-down · Pressure & vacuum · TDC location |
| Display | Digital touchscreen with on-screen test shortcuts and instructions |
| Sensors | Digital pressure and vacuum sensors for repeatable readings |
| Data logging | Automatic per cylinder; chart view compares all cylinders on one screen |
| Leak-down calculation | Automatic leak % at a 100 PSI reference input — no manual math |
| Vacuum units | inHg, kPa or PSI, switchable on the display |
| Vacuum modes | High / low range, plus live graph-over-time |
| Cylinders supported | Up to 8 cylinders, each logged and compared separately |
| Engine compatibility | Gasoline engines. Not for diesel engines. |
| Adapters | Multiple spark-plug adapters and quick-connect fittings included |
| Also required | Ratchet to turn the crankshaft (TDC / leak-down) · air compressor at 100 PSI (leak-down only) |
| Shipped weight & package | 4 lb · 15.5 × 11 × 2 in |
| Warranty | 5-year 100% full coverage — manufacturer and operational defects, USA-based fast replacement |
What's in the box
- Proton digital cylinder gauge, with the one-way valve and plunger (bleed) valve on the unit
- Cylinder hose that threads into the spark-plug hole
- Extension hose for hard-to-reach cylinders
- Engine cylinder adapters for a range of spark-plug threads and reaches
- Quick-connect fittings and accessories
Who it's for
Repair shops and professional technicians. Compression and leak-down are routine work, and the time cost is usually in the record-keeping, not the testing. Automatic per-cylinder logging and a single comparison screen cut the paperwork out of the job and make the result easier to show a customer.
Mobile mechanics. One compact case does the work of a compression tester, a leak-down tester, a vacuum gauge, and whatever you were using to find TDC.
Engine builders and performance shops. Leak percentage calculated to the same 100 PSI reference every time makes cylinder-to-cylinder and before/after comparisons meaningful.
DIY mechanics. If you're chasing a misfire, a rough idle, or a suspected head gasket, this tells you which cylinder is down and then which component is letting go — the two questions that decide whether an engine comes apart.
Digital vs. a traditional analog setup
Running the tests
Proton compared with a conventional analog compression gauge plus a separate dual-gauge leak-down tester.
Included
Available
Not available
| Capability | PROTON Cylinder Gauge | Analog compression + leak-down kit |
|---|---|---|
| Compression testing | Yes | Yes |
| Cylinder leak-down testing | Yes | Yes |
| Leak % calculated for you | YesAutomatic at 100 PSI | NoYou do the math |
| Readings logged per cylinder | YesAutomatic | NoPen and paper |
| All cylinders compared on one screen | Yes | No |
| Manifold vacuum testing | YesLive graph over time | NoSeparate gauge needed |
| TDC location assistance | YesBy pressure & vacuum | NoScrewdriver / timing marks |
| Switchable units (inHg / kPa / PSI) | Yes | No |
| Tools to buy and carry | OneSingle case | Three or fourPlus a way to find TDC |
Analog kits are proven, inexpensive, and need no charging — if you run a compression test twice a year, one is hard to beat on price. The Proton earns its place when you test often enough that the logging, the automatic leak math, and having one kit instead of four save real time.
Warranty and support
Every Proton is covered by a 5-year 100% full-coverage warranty against manufacturer and operational defects. AutoLine Pro is an American family-owned business, and support is USA-based — if a unit fails, we replace it, fast. Questions before you buy? Reach us through the contact form.
The Proton is designed for gasoline engines. Diesel compression testing requires higher-range gauges and injector or glow-plug-port adapters, and is not supported by this tool.
How to Use the PROTON Cylinder Gauge
FAQs
Will it work on my engine?
It replaces four separate tools with one touchscreen unit: a digital compression tester, a cylinder leak-down tester, a pressure & vacuum gauge, and a top dead center (TDC) assistant. Every reading is logged automatically to the cylinder it came from, and a single chart screen shows all cylinders side by side so a weak one is obvious at a glance.
Up to 8 cylinders. Each cylinder is selected on screen and its compression and leak-down results are stored separately, so 4-, 6- and 8-cylinder engines are all covered.
No. The Proton is built for gasoline engines. Diesel compression testing runs at far higher pressures and needs injector- or glow-plug-port adapters, so use a dedicated diesel compression kit for those engines.
The kit includes multiple spark-plug adapters covering the common thread sizes and reaches, plus quick-connect fittings and an extension hose for cylinders buried under intake plumbing or set back against the firewall. If you have an unusual thread size, check it against the included adapters before ordering — message us through the contact form and we'll tell you straight.
Only for the leak-down test, which needs shop air at a 100 PSI reference input. The compression test, the vacuum test and TDC location all work without one. You'll also want a ratchet and socket to turn the crankshaft for TDC and leak-down.
It works on any gasoline engine whose spark-plug thread matches one of the included adapters and that you can crank or turn over by hand. Small-engine and powersports plug threads vary a lot, so check your plug size against the adapter set first.
How do I run the tests?
Yes — every plug and all the ignition coils, not just the cylinder you're testing. With the other plugs still in, the engine cranks slowly and the cylinder you're measuring never reaches its true peak pressure. Pull the fuel-pump fuse or relay first so the injectors aren't spraying fuel into open cylinders while you crank.
Connect the hose to the cylinder, open the pressure/vacuum screen, and turn the crankshaft by hand with a ratchet. When pressure starts building you're on the compression stroke. When pressure stops rising and a small amount of vacuum appears, you've just passed TDC — back the ratchet up slightly, then nudge back and forth until neither pressure nor vacuum changes. That dead spot is TDC with both valves closed, and it's required before a leak-down test means anything.
Yes. Dial the regulator until the input gauge reads 100 PSI and the unit calculates and displays the leak percentage automatically. With a traditional analog dual-gauge tester you set 100 PSI and then work the percentage out yourself, cylinder by cylinder.
As a general rule: under 10% is healthy on a well-maintained engine, 10–20% is worth monitoring and is common on high-mileage or performance engines, and over 20% usually means a real mechanical problem. Consistency across cylinders matters as much as any single number.
The spread between cylinders matters more than the absolute figure. A common shop standard is that no cylinder should be more than about 10% below the highest (some manufacturers allow 15%, and some publish a hard minimum — check the service data for your engine). Two adjacent cylinders low together is the classic head-gasket pattern.
Listen while the cylinder is pressurized. Air out the throttle body or intake means a leaking intake valve. Out the tailpipe means an exhaust valve. Out the oil filler, dipstick tube or PCV means piston rings or a worn bore. Bubbles in the coolant, or air crossing into the neighbouring cylinder, points at the head gasket.
Compression first. It's quicker and tells you which cylinder is down. Then run leak-down on the suspect cylinders to find out why — valve, rings, or head gasket. Having both tests in one unit with shared logging is what makes running them back-to-back practical.
Yes. Press the chart button and every cylinder number appears across the top with its compression or leak-down figure beneath, on one screen. That's the view that makes a weak cylinder jump out, and it's easy to show a customer.
Is it the right buy?
An analog gauge gives you one number at a time and leaves you to write it down. The Proton logs every reading to its cylinder, does the leak-down math for you at 100 PSI, adds a manifold vacuum gauge with a live graph over time, and helps you find TDC by pressure and vacuum instead of a screwdriver down the plug hole. Analog kits are proven and cheap — if you test twice a year, one is hard to beat on price. The Proton earns its place when you test often enough that the logging and the automatic math save real time.
The Proton digital cylinder gauge (with the one-way valve and plunger bleed valve on the unit), the cylinder hose that threads into the spark-plug hole, an extension hose for hard-to-reach cylinders, the engine cylinder adapters, and the quick-connect fittings and accessories.
Yes, if you're comfortable pulling spark plugs and coils. The touchscreen walks you through each test with on-screen shortcuts and instructions, and the unit handles the part people get wrong — the leak percentage math and keeping track of which reading belongs to which cylinder. The one step worth reading up on first is finding top dead center.
A 5-year 100% full-coverage warranty against manufacturer and operational defects. AutoLine Pro is an American family-owned business and support is USA-based — if a unit fails, we replace it, fast. Questions before you buy? Reach us through the contact form.