6.5L GM/Detroit Diesel

6.5L Diesel Specs, History, & Information

The GM/Detroit 6.5L diesel was rolled out for the 1992 model year and offered alongside the 6.2L, which would be retired after the 1993 model year. At this point, the diesel marketplace was headed in such a direction that the truck/engine combination that could work the hardest while using the least amount of fuel would reign supreme. Ford was dominating in sales, and the 6.2L wasn't attracting the attention that Ford's IDI and Dodge's Cummins powered pickups were. The result was a new engine, roughly based on the 6.2L, that would supplement what the 6.2L was known for while boosting performance significantly to prove that GMC and Chevrolet pickups could run with the herd.

GM's government contracts continued, and though 2000 was the final model year of the 6.5L for GMC and Chevy, engine production continued through Humvee manufacturer AM General under license from General Motors. The 6.2L and 6.5L diesels are dimensionally similar, and thus most exterior bolt-on components are interchangeable between the two engines. Like its predecessor, the 6.5L bellhousing bolt pattern and engine mounts are identical to those of GM V-8 gasoline engines.

6.5L GM Diesel Specs

Manufacturer:

Detroit Diesel (a division of GM at the time)

Production Years:

1992-2000; currently still used in military applications, produced by AM General

Applications:

Chevrolet/GMC: Tahoe, Yukon, Suburban, C/K pickups, 2500 & 3500 trucks.
AM General: Hummer & HMMWV

Configuration:

90° V-8

Block/Head Material:

Cast iron block, cast iron heads

Displacement:

395 cubic inches, 6.5 liters

Firing Order:

1-8-7-2-6-5-4-3

Cylinder Numbers:

6.5L GM, Detroit diesel cylinder numbers

Compression:

18:1 to 21.5:1 depending on year & application

Compression Test Pressure:

Minimum 380 psi (dry test, do NOT perform a wet compression test). Cylinder with lowest pressure should be within 80% of cylinder with highest pressure.

Bore:

4.055 inches

Stroke:

3.818 inches

Injection:

IDI (indirect injection), Stanadyne DS-4 injection pump

Aspiration:

Turbocharged (5 - 8 psi maximum MAP) and naturally aspirated versions produced

Oil Capacity*:

7 qts w/ filter up to 1998 model year, 8 qts w/ filter 1999+ model year. Use oil filter AC Delco PF35, all model years.

Max Engine Speed:

3,400 rpm (governed engine speed may be as low as 3,000 rpm in certain applications)

Horsepower:

• 180 hp @ 3,400 rpm (introductory)
• 215 hp @ 3,200 rpm (max)

Torque:

• 360 lb-ft @ 1,700 (introductory)
• 440 lb-ft. @ 1,800 rpm (max)

Engine Weight:

Approx. 750 lbs

Nominal Engine Dimensions:

Length:

30"

Width:

26"

Height:

26"

* Always check oil level after refilling crankcase.

The 6.5L Detroit diesel maintained the fuel efficient image that was used to market its predecessor. A variety of applications used the 6.5L, and as such several versions were produced. A special "Fuel Miser" 6.5L surfaced in Chevrolet's P trucks (delivery trucks), for example. Additionally, turbocharged and naturally aspirated versions were made available. Common 6.5L problems include cracks propagating in the main caps and crankshaft failures from aging/fatigue of the harmonic balancer. Overheating issues are also common, and have been known to lead to cracked cylinder heads amongst other failures. The 6.5L diesel was retired to make way for GM/Isuzu's Duramax diesel, launched for the 2001 model year.

6.5L Diesel Variations and RPO Codes

Variation

Description

L12

Turbocharged, standard engine

L49

Naturally aspirated, standard engine

L56

Turbocharged, emissions controlled (EGR & catalytic converters); used in all light duty 1/2 & 3/4 ton trucks

L57

Naturally aspirated, high output (HO)

L65

Turbocharged, heavy duty 3/4 & 1 ton trucks, high output (HO)

LQM

175 hp @ 2,800 rpm

LQN

190 hp @ 2,800 rpm

"Fuel Miser"

120 hp, 260 lb-ft. torque, optional in Chevrolet P trucks

6.5L Diesel Horsepower & Torque Curve

6.5L GM diesel horsepower and torque curves

2000 model year 6.5L L65 diesel horsepower and torque curves.

6.5L Diesel Oil Spec and Service Intervals

For all model year 6.5L turbocharged and naturally aspirated diesels the engine oil and filter is required to be changed every 5,000 miles/12 months under normal operating conditions or every 2,500 miles/3 months under severe operating conditions (periods of excessive idle, towing, frequent short trips, stop-and-go traffic, etc).

Oil Viscosity

Acceptable Temperature Range

Notes

SAE 30

ambient temperature > 32° F

Recommended in consistently hot ambient temperatures. Not preferred in cooler temperatures, use 15W-40.

SAE 15W-40

ambient temperature > 0° F

Preferred viscosity within temperature range unless ambient temperature is consistently hot.

SAE 10W-30

ambient temperature < 60° F

Required cold weather viscosity.

In addition to adhering to the engine oil viscosity chart above, the following block heater schedule should be used in cold weather:

Oil Viscosity

Ambient Temp > 32° F

Ambient Temp 32° F to 0° F

Ambient Temp < 0° F

SAE 30

block heater not required

use block heater min 2 hours

use block heater min 8 hours

SAE 15W-40

block heater not required

block heater not required

use block heater min 8 hours

SAE 10W-30

block heater not required

block heater not required

use block heater min 8 hours

 

6.5L Diesel PMD/FSD Failures

PMD failures are arguably the most commonly experienced problem with the 6.5L diesel. The PMD, or Pump Mounted Driver is an electronic module affixed to the side of the injection pump that controls the fuel solenoid. It is also often referred to as the FSD, or Fuel Solenoid Driver. The PMD's fatal flaw is its location on the driver side of the injection pump, which sits in the engine valley. While energized, the PMD generates an intense amount of heat, which does not properly dissipate (do to its location) and ultimately leads to the module's demise. Most hard start, no start, and engine stalling concerns are attributed to a failed or failing PMD. It is extremely common for owners to mount the driver in a remote location and/or install an aftermarket heat sink to a relocated PMD to keep it from overheating. While the PMD/FSD is certainly the 6.5 diesel's Achilles heal, concerns are easily remedied thanks to response from the aftermarket.