18NA098

Bulletin No.:
Service Bulletin
Date:
18-NA-098
November, 2020
INFORMATION
Subject:
Brand:
Chevrolet
GMC
Diagnostic Tip for Coolant Leak, Coolant Consumption and/or Low Coolant Message
Being Displayed On the Driver Information Center (DIC)
Model:
Model Year:
from
to
Silverado
2017
2018
Silverado 2500/3500
2019
2021
Silverado 4500HD,
5500HD and 6500HD
2019
2021
Sierra
2017
2018
Sierra 2500/3500
2019
2021
VIN:
from
to
Engine:
Transmission:
Equipped
with 6.6L
Diesel
Engine (RPO
L5P, L5D)
Involved Region or Country
North America and Middle East
Condition
Some customers may comment on a coolant leak, coolant consumption and/or low
coolant message being displayed on the driver information center (DIC).
Correction
Use the illustrations below, that show the areas in blue, to help identify where to look for
possible coolant leak paths for the Duramax engine.
5027608
1. Plugs in Cylinder Head (PLUG, CYL HD CORE
HOLE) (Qty 8)
2. Block Heater (HEATER, ENG COOL)
3. Cup Plugs in Block (PLUG, ENG BLK COOL DRN
HOLE (OD=40MM) (Qty 5)
Copyright 2020 General Motors LLC. All Rights Reserved.
Page 2
November, 2020
Bulletin No.: 18-NA-098
5027641
1. Coolant Hose and Clamp
2. Thermostat Housing (SEAL, ENG COOL THERM
(O RING)
3. O-Ring for Bypass Pipe (SEAL, THERM BYPASS
PIPE (O RING))
4. Flange with Gasket for Bypass Pipe (GASKET,
THERM BYPASS PIPE)
5. O-Ring Seal (Front Cover to Water Pump) (SEAL,
W/PMP CVR)
6. Seal-Water Pump to Pipe (GASKET, W/PMP
OTLT PIPE)
7. Coolant Hose and Clamp
8. Cup Plug on Block (PLUG, ENG BLK COOL
DRN HOLE)
5028324
1. O-Ring (Water Pipe to Oil Cooler) (SEAL, W/PMP
OTLT PORT)
2. Either end of the Oil Cooler Adapter (Elbow)
(GASKET, ENG OIL CLR ADAP)
3. Seal in the Oil Coolet (GASKET, ENG OIL CLR)
Note: Ghost view of the Oil Cooler to reveal O-ring and
cover gasket and 2 adapter gaskets (Oil Filter not
shown).
Bulletin No.: 18-NA-098
November, 2020
Page 3
5028590
1. Cup Plugs (Qty 2)(One per side in rear of Cylinder
Head) (PLUG, CYL HD CORE HOLE)
2. Gaskets under Flange, 1 location on EGR Bypass
Valve (Serviced with VALVE, EGR VLV CLR
BYPASS)
3. Hose Clamps, 5 locations
4. Turbo Coolant Feed Pipe (GASKET, TURBO
COOL FEED & RTN PIPE)
5. Gaskets under Flange, 2 locations on EGR Valve
(Service with VALVE, EGR)
6. Cup Plug in Bypass Valve (Service with
VALVE, EGR)
7. Cover on Flywheel Housing (GASKET, FLYWHL
HSG CVR)
1. Gasket for Turbo coolant pipes (GASKET, TURBO
COOL FEED & RTN PIPE) (Qty 2)
2. Ghost view of Upper Intake Manifold and ERG
Coolant Pipe. Inlet Adapter removed to reveal EGR
Coolant Return Pipe.
3. Hose Clamps for Turbo Coolant Pipes and DEF
Coolant Pipe (Qty6)
5028604
Note: A leak on the top of the engine will trail down the
back of the engine and appear as a rear cover leak.
5028593
1. Hose Clamps on the EGR Coolant Return Hose
(Qty 2)
2. O-Ring for EGR Coolant Return Pipe (SEAL, EGR
COOL FEED PIPE) (Qty 2)
3. Gaskets under Flanges for EGR Coolant Feed and
Return Pipes (SEAL, EGR COOL FEED PIPE)
(Qty 2)
Page 4
November, 2020
Bulletin No.: 18-NA-098
5028676
1. Gaskets between Cylinder, Heads and Water
Crossover Housing (GASKET, ENG COOL
THERM HSG) (Qty 2)
2. Head Gaskets (GASKET, CYL HD)
Version
3
Modified
Released April 05, 2018
Revised July 25, 2018 - Added the 2019 to Model Year.
Revised June 24, 2019 – Added the 2020 Model Year.
Revised November 06, 2020 — Added 2021 Model Year and Silverado 4500HD, 5500HD
and 6500HD
GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these
technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper
service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a
job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your
vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the
information.
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