Safety Warning

DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.

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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 880 (ENGINE COOLING SYSTEM)REPAIR INSTRUCTIONSTHERMOSTAT BYPASS PIPES REPLACEMENTINSTALLATION PROCEDURE

1999 GMC Forward Control 5.7 R, Automatic

Installation Procedure

1999 GMC Forward Control 5.7 R, AutomaticSECTION Installation Procedure

WARNING: This page is about a different car, the 2003 Pontiac Aztek and 2003 Buick Rendezvous. However, it is still accessible from the selected car via links, so may be relevant.

Apply engine coolant to the bypass pipe seal in order to ease installation.
Install the thermostat bypass pipe.
Install the thermostat bypass pipe hose.

Fig 1: Installing Thermostat Bypass Pipe Hose
Courtesy of GENERAL MOTORS CORP.
Install the thermostat bypass pipe hose clamp (5).
NOTE: Refer to FASTENER NOTICE in Cautions and Notices.
Install the thermostat bypass pipe bolt (4).
Tighten

Tighten the thermostat bypass pipe bolt to 11 N.m (98 lb in).
Install the thermostat bypass pipe to cylinder head nut (3).
Tighten

Tighten the thermostat bypass pipe nut to 25 N.m (18 lb ft).
Install the thermostat bypass pipe to throttle body hose clamps (1).

Fig 2: Installing Thermostat Bypass Pipe Bolt
Courtesy of GENERAL MOTORS CORP.
Install the thermostat bypass pipe to throttle body nut.
Tighten

Tighten the thermostat bypass pipe nut to 25 N.m (18 lb ft).
Install the heater hose to the bypass pipe.
Install the left engine mount strut to the engine.
Install the upper radiator hose to the engine.
Install the air inlet duct. Refer to in Engine Controls - 3.4L.
Install the spark plug wire harness to the thermostat bypass pipe.
Fill the cooling system. Refer to DRAINING AND FILLING COOLING SYSTEM .

Fig 3: Installing Thermostat Bypass Pipe Nut

Courtesy of GENERAL MOTORS CORP.

RENDER: 1.0x

NO RELATED

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.
• Brakes feel soft, pull hard to one side, or make grinding noises.
• The engine overheats, stalls repeatedly, or misfires under load.
• You are missing required tools, torque specs, or safe lifting equipment.
• You are not confident in the next step or safety outcome.