Alignment Diagnostics and Fleets
Cylinder Leak-Down Percentage Calculator
Calculate pressure-loss percentage from leak-down tester readings. Many dual-gauge testers use device-specific calibration and scales.
Replace the example values
Check labels, prefixes, suffixes, and percentage bases before calculating.
Purpose and reference point
Calculate pressure-loss percentage from leak-down tester readings — reference values, sensor readings, and physical measurements should remain separately labeled.
Many dual-gauge testers use device-specific calibration and scales — that condition defines when calculated leak-down is comparable with another result.
A sensor or comparison value can narrow an investigation, but it cannot identify the failed part without the specified physical tests — for tester supply pressure, the page specifically expects regulated reference pressure.
If the next task is to calculate fleet availability from scheduled vehicle-days and downtime, continue with the Fleet Availability.
Vehicle data needed here
Tester supply pressure: Regulated reference pressure — a compatible entry should record gauge type, temperature, and whether the value is absolute or relative pressure.
The Cylinder-side pressure entry represents pressure retained on the cylinder side — before calculating, record gauge type, temperature, and whether the value is absolute or relative pressure.
Tester calibration offset is defined here as optional correction established during tester calibration — keeping that definition intact requires you to measure from the stated reference points and note whether the vehicle or component is loaded.
How the result is derived
In “leak-down percentage = supply-pressure loss ÷ regulated supply pressure,” the relationship answers the question stated above without adding an unstated correction factor.
No term beyond tester supply pressure, cylinder-side pressure, and tester calibration offset is introduced in “leak-down percentage = supply-pressure loss ÷ regulated supply pressure.”
What a changed result indicates
Calculated leak-down answers “Calculate pressure-loss percentage from leak-down tester readings.”
Piston position, temperature, ring seating, and leakage path affect diagnosis — when that condition changes, compare separate calculator runs instead of blending the inputs.
Reproducing the sample result
Using the loaded case, the recorded inputs are Tester supply pressure = 100 psi, Cylinder-side pressure = 92 psi, and Tester calibration offset = 0 psi.
For that data set, the calculator returns Calculated leak-down = 8.0%.
A related vehicle record may need to calculate total toe and side-to-side difference from individual wheel angles, a relationship covered by the Total Toe Angle.
A useful calculation record
For Cylinder Leak-Down Percentage, the raw notes should preserve both tester supply pressure—defined as regulated reference pressure—and tester calibration offset, meaning optional correction established during tester calibration.
When reviewing the result later, use “Many dual-gauge testers use device-specific calibration and scales” as the test for whether the original operating case still applies.
Input and comparison questions
What measurement source fits Tester supply pressure when it represents regulated reference pressure?
Because tester supply pressure represents regulated reference pressure, use a source tied to the exact vehicle, component, and operating period described by the other fields.
How does the warning “Many dual-gauge testers use device-specific calibration and scales” affect Calculated leak-down?
The condition “Many dual-gauge testers use device-specific calibration and scales” is not corrected automatically by the numeric inputs, so create a separate cylinder leak-down percentage case when it changes.
What assumption is expressed by “leak-down percentage = supply-pressure loss ÷ regulated supply pressure”?
In “leak-down percentage = supply-pressure loss ÷ regulated supply pressure,” tester supply pressure and cylinder-side pressure are treated as parts of one vehicle case.
How narrowly is Cylinder-side pressure defined by “Pressure retained on the cylinder side”?
The definition “Pressure retained on the cylinder side” excludes a similarly named rating or a measurement taken at another reference point.