One cylinder tells you nothing; the spread tells you everything
A compression test is read as a comparison between cylinders, not as an absolute number: the figure that means something is the spread, and the manufacturer publishes the tolerance. The practical split is between petrol and diesel kits, and they are not interchangeable — diesel runs far higher pressures and needs injector or glow-plug adapters rather than spark-plug threads. What then separates kits is the adapter set: thread sizes, reach, and whether a long flexible hose can get to a recessed plug without removing half the intake. We compare gauge range and units, adapter threads supplied, hose length and flexibility, the release valve, and what the case actually holds.
Petrol · 0–300 psi / 0–20 bar · M10, M12, M14, M18 adapters · 7.6 cm (3 in) gauge · two rubber cone ends
The cheapest complete petrol kit here, and it includes the two rubber cone ends that let you take a reading without threading anything into the head.
Best for: A first compression test on a petrol engine, where the spread between cylinders is the answer.
≈ $17
Petrol · 0–20 bar / 0–300 psi · M10, M12, M14, M18 × stated pitches · for wear on rings and valves
The kit that publishes its thread pitches as well as its diameters — the specification that decides whether an adapter actually seals in your head.
Best for: Someone who has checked their plug thread and wants the adapter to match exactly.
Petrol · 0–300 psi / 0–20 kg (0 to 44.1 lb)/cm² · 4 thread adapters including M10 for motorcycles · 2 rubber cones
A petrol kit whose listing names the M10 adapter as the motorcycle size — a small honesty that tells you the maker knows what the set is used for.
Best for: A household with a car and a motorcycle, where one kit should cover both.
Petrol · analog dial 0–20 bar / 0–300 psi / 0–2000 kPa · adapter hose or rubber cone tube · M10–M18
The workshop-brand version: an analog dial with three scales, an adapter hose and a rubber cone tube, from a maker whose catalog numbers mean something.
Best for: Someone who expects to still own this in fifteen years.
≈ $105
Diesel · 0–70 bar / 1000 psi · 17-piece · rotating quick coupler · pressure release valve · copper and steel
The diesel kit, and the reason a petrol tester cannot be used on a diesel: 70 bar rather than 20, with injector and glow plug adapters instead of spark plug threads.
Best for: A diesel car, van or tractor — where a petrol gauge would read off the top of its scale.
The gauge range has to take in the values expected from the engine tested. A gauge that stops too low saturates and says nothing.
Spark plug threads vary. The number of adapters decides which engines the tool can be used on.
A short hose will not reach down a fifteen-centimeter plug well on a modern engine. The stated hose length decides what can be tested without removing the manifold.
Engine at temperature, all plugs removed, throttle held open, and cranking over several revolutions. Every condition counts.
Yes: leaving the others in slows the cranking and falsifies the values downwards.
It depends on the engine. It is the difference between cylinders that diagnoses best: one cylinder markedly below the others signals a fault.
Rings, valves or head gasket. Repeating the test with a little oil in the cylinder points between rings and valves.
Absolutely: with the throttle closed, the cylinder does not draw in enough and every value drops.
An engine at temperature gives representative values. Cold, the clearances differ and the values are lower.
Compression measures what the cylinder produces; the leak-down test injects air and listens for where it escapes. The second one locates.
It is the spread between cylinders, more than the absolute figure, that says something: one cylinder well below the others points to a local problem. The manufacturer gives the minimum acceptable value.
It is the difference between cylinders that diagnoses, not the absolute value. All plugs removed, throttle open, engine warm — every missing condition drops all the values — and a little oil in the cylinder tells rings from valves.
A column is opened only if four tools in five publish its value. Otherwise the table would compare what nobody has measured.
| Model | Price | Engine type | Gauge | Thread adapters |
|---|---|---|---|---|
| DAYUAN YT-103242 | $17 | Petrol, stated | 7.6 cm (3 in) dial, dual scale 0–300 psi and 0–20 bar, stated | M10, M12, M14, M18 with O-rings, stated |
| BGS 9669 | $105 | Petrol, stated | Analog dial, 0–300 psi / 0–2000 kPa / 0–20 bar, stated | M10 × 1.0, M12 × 1.25, M14 × 1.25, M18 × 1.5 — stated |
| Awsuc AW-177 | — | Petrol, stated | Dual scale 0–300 psi and 0–20 kg (0 to 44.1 lb)/cm², stated | 4 sizes; M10 stated as suitable for motorcycles |
| DHA195 | — | Diesel — cars, tractors and trucks, stated | 0–70 bar / 1000 psi, stated | — |
| FreeTec FY65011 | — | Petrol, stated | 0–20 bar / 0–300 psi, stated | M10 × 1.0, M12 × 1.25, M14 × 1.25, M18 × 1.5 — stated |
Specifications: manufacturer sheets for garage tools and the matching Amazon product pages. Prices and availability: Keepa. Every figure in this table names its source.
Most recent revision in this category: September 4, 2026.
Prices quoted in these summaries are dated readings. The live price is shown next to each product.
