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GM Gen V small-block V8 platform

6.6L V8 Gasoline (GM HD, L8T 2020+)

2020-present · 6.6L · General Motors

52

vehicle configs

5

failure modes

14

parts

3

recipes

recalls + bulletins →

symptoms compared →

buyer's checklist →

Failure modes

Intake-valve carbon buildup (direct injection, no port wash)

Cooling system wear: water pump, hoses, thermostat (towing duty)

Direct-injection high-pressure fuel pump / injector failures

Ignition service wear: spark plugs and coils

Valvetrain hardware failures: lifters, valves (no AFM - attribution guard)

Parts

gm-hd-gas-l8t: oil-catch-can-kit (honest catalog gap) part-l8t-catch-can-gap gm-hd-gas-l8t: coolant (service item) part-l8t-coolant-service gm-hd-gas-l8t: cylinder-head (honest catalog gap) part-l8t-cylinder-head-gap gm-hd-gas-l8t: fuel-filter (honest catalog gap) part-l8t-fuel-filter-gap gm-hd-gas-l8t: hpfp (honest catalog gap) part-l8t-hpfp-gap gm-hd-gas-l8t: ignition-coil (honest catalog gap) part-l8t-ignition-coil-gap gm-hd-gas-l8t: injector (honest catalog gap) part-l8t-injector-gap gm-hd-gas-l8t: intake-valve-cleaning-service (service item) part-l8t-intake-carbon-service gm-hd-gas-l8t: engine-long-block (honest catalog gap) part-l8t-long-block-gap 6.6L L8T Spark Plug (OEM) part-l8t-spark-plug 6.6L L8T Spark Plug Wire (OEM) part-l8t-spark-plug-wire 6.6L L8T Spark Plug Wire Kit (OEM) part-l8t-spark-plug-wire-kit 6.6L L8T Thermostat Kit (OEM) part-l8t-thermostat-kit 6.6L L8T Water Pump (OEM) part-l8t-water-pump

Recipes

Cooling inspection and wear-item service for the 6.6L L8T on a towing HD truck: pressure-test, weep hole, hoses, thermostat (mode fm-l8t-cooling-wear)

L8T ignition service (mode fm-l8t-ignition): no L8T-specific defect exists - this is conventional Gen V truck hardware on service intervals, and the honest recipe is interval discipline

Rough idle or hesitation on a high-mileage 6.6L L8T: direct injection leaves the intake valves unwashed - borescope before cleaning, and rule out ignition and injectors (same symptoms) (mode fm-l8t-carbon)

Reference for this engine

Repair costs for this engine

2 failures priced in parts

Part number lookup

every OEM number we verified

Is this the engine in my truck?

the 8th character of the VIN

Vehicle configurations