From grimoire
Diagnoses vehicle cooling system failures by pressure-testing and inspecting components. Use for overheating, coolant loss, heater problems, or temperature gauge anomalies.
How this skill is triggered — by the user, by Claude, or both
Slash command
/grimoire:diagnose-cooling-system-failureThe summary Claude sees in its skill listing — used to decide when to auto-load this skill
Systematically pressure-test and inspect the cooling system to identify leaks, blockages, thermostat failure, or head gasket compromise before the engine is driven and damaged further.
Systematically pressure-test and inspect the cooling system to identify leaks, blockages, thermostat failure, or head gasket compromise before the engine is driven and damaged further.
Adopted by: ASE A1 Engine Repair certification dedicates a major section to cooling system diagnosis. Gates Corporation and Prestone publish industry-standard cooling system diagnostic guides used by shop technicians. All OEM service manuals require a pressure test before any coolant-related diagnosis or repair. Impact: Overheating is the most damaging condition a car engine can experience — one overheating event can warp cylinder heads ($1,000–$3,000), crack a head gasket ($1,500–$4,000), or seize bearings (total engine replacement: $3,000–$8,000). Many cooling system failures present identically in symptoms but have different root causes: a leaking hose, a stuck thermostat, a failed water pump, and a blown head gasket all cause overheating. Driving with any of these undiagnosed causes escalating damage.
A hot cooling system is pressurized to 15+ PSI. Opening the radiator cap or overflow reservoir on a hot engine ejects scalding coolant.
Rule: never open coolant system when engine is hot. Wait 30–60 minutes after shutdown, or wrap the cap in a thick cloth and open slowly, releasing pressure gradually before removing.
| Symptom | Initial suspects |
|---|---|
| Overheating (temp gauge high) | Thermostat stuck closed, low coolant, radiator blocked, water pump failure |
| Temperature gauge never reaches normal | Thermostat stuck open |
| Coolant disappearing without visible leak | Head gasket (internal leak), leaking heater core |
| White smoke from exhaust | Head gasket failure (coolant burning in combustion chamber) |
| Heater blowing cold (engine hot) | Low coolant level, thermostat stuck open, clogged heater core |
| Bubbling in coolant reservoir when engine running | Head gasket (combustion gases entering cooling system) |
| Milky oil on dipstick | Head gasket (coolant mixing with oil — critical; do not drive) |
With engine cool:
Do not add coolant to a hot, empty system (thermal shock to metal parts).
A cooling system pressure tester ($20–$40 rental) pressurizes the system to simulate operating conditions:
Locate the external leak:
A stuck-closed thermostat prevents coolant from reaching the radiator; a stuck-open thermostat prevents warmup:
Test procedure:
Head gasket diagnosis if external pressure test found no leak:
Combustion gas (CO2) test:
Additional head gasket indicators:
| Finding | Correct action |
|---|---|
| External hose leak | Replace hose; refill coolant |
| Radiator leak | Repair or replace radiator |
| Thermostat stuck | Replace thermostat |
| Water pump leak | Replace water pump (typically requires timing belt/chain access) |
| Head gasket failure | Engine teardown; machining may be required for warped head |
| No leak found | Check fans (electric fan fuse/relay; mechanical clutch fan function) |
npx claudepluginhub jeffreytse/grimoire --plugin grimoireInspects vehicle fluids (engine oil, coolant, brake, power steering, transmission, washer) for level and condition to catch leaks and degradation early.
Diagnoses failures, fixes bugs, and investigates failing tests using systematic debugging: reproduce first, read before changing, assume nothing, find root cause.
Enforces systematic root cause analysis for bugs, test failures, unexpected behavior, and regressions via five-phase workflow: Understand, Reproduce, Isolate, Fix, Verify.