GM 12689039
Thermostat Housing

Replacement of the engine coolant Thermostat housing (RPO LNJ) (3.4L) should begin by removing the fuel injector sight shield first. Pump out coolant until you reach a level below the measurement position of the Thermostat. Start the procedure by disconnecting both pipes from the Thermostat housing: crossover Exhaust Pipe and Radiator Hose. Begin by cleaning the Thermostat housing bolts threads before removing both the Thermostat housing and Thermostat. Caretfully clean both surfaces before installing the Thermostat while mounting it into the housing. Use gm p/n 12378478 (Canadian P/N 88900041) or an equivalent rtv sealer on the Thermostat housing bolt threads before installing the Thermostat housing bolts to 25 n.m (18 lb ft) torque specifications. After reconnecting the Radiator Hose to the Thermostat housing install the crossover Exhaust Pipe. To complete the procedure install the fuel injector sight shield, fill the cooling system and perform leak inspections while repairing as needed.

You must remove the fuel injector sight shield before starting the engine coolant Thermostat housing (LNJ) (3.4L) replacement task. Pull the coolant until it sits beneath the Thermostat position. The next step requires deletion of both crossover Exhaust Pipe and Radiator Hose present at the Thermostat housing. After removing the Thermostat housing bolts begin cleaning off any sealer from the bolt threads before separating the Thermostat housing and the Thermostat. Mount the heating control component first then put on the Thermostat housing after cleaning all mating areas properly. Use rtv sealer type gm p/n 12378478 (or Canadian P/N 88900041 equivalent) on the bolt threads of the Thermostat housing. Screw in the Thermostat housing bolts until they reach 25 nm of torque (18 lb ft). After reattaching the Radiator Hose to the Thermostat housing install the crossover Exhaust Pipe. To complete the task reinstall the fuel injector sight shield while you fill the cooling system and conduct leak detection followed by any needed repair work.

Draining engine block coolant at the Water Pump drain portion marks the first step for replacing the laf engine coolant Thermostat housing. After draining, ensure the drain bolt remains tight. Begin by lowering the vehicle then disconnect the engine wiring harness electrical connector at the engine coolant temperature (ECT) sensor. Start by clearing both the heated oxygen sensor (HO2S) electrical connector rosebud clip and relocating the radiator outlet hose clamp before removing the radiator outlet hose from the Thermostat housing. To proceed, users should first remove all Exhaust Heat Shield studs along with the Exhaust Heat Shield itself. The hvac heater inlet hose and outlet hose need removal from the Thermostat housing. Before removing the components start by raising your vehicle and removing the ect sensor if needed followed by both Thermostat housing bolts. Screw-tighten the water transfer pipe as you pull for removal from the Water Pump followed by removing the Thermostat and the water transfer pipe from the Thermostat housing (if applicable). Following the removal of water transfer pipe o-ring seals when needed discard them before removing the Thermostat cover bolts and cover. All debris and thread sealant needs to be cleaned from both ect sensor holes and bolt openings whenever reusing the housing. The installation process requires two steps: first place new Thermostat cover o-ring seals into the recess groove and then install the Thermostat (if required) before tightening the cover bolts to 10 nm (89 lb in). Place the new Thermostat housing to engine gasket on the Thermostat housing before positioning the assembly then applying a light coating of coolant on the water feed pipe seals. Start by putting new o-ring seals on the water feed pipe after you've treated them with coolant. Position the water feed pipe through the Thermostat housing while you guide the locator tab and adjust the water pipe to the Water Pump. Push the water feed o-ring seal toward the Water Pump until it reaches its proper seating position without damaging it. Then position the Thermostat housing against the engine block and torque the Thermostat housing bolts to 10 nm (89 lb in). Installation of the ect sensor requires a 20 nm torque (15 lb ft) where you should first coat its threads with sealant. Lower the vehicle and attach the hvac heater inlet hose with the hvac heater outlet hose to the Thermostat housing. You should replace the Exhaust Heat Shield followed by attaching the radiator outlet hose to the Thermostat housing before securing the radiator outlet hose clamp. Secure the engine wiring harness electrical connector to the ect sensor then add the ho2s electrical connector rosebud clip at the Thermostat housing. Lower the vehicle then open drain valves both at the radiator and Water Pump while filling the cooling system.

Take off the thermostat and clean the mating surfaces.

Install the water outlet housing bolts and tighten them to 10 N.m (89 lb in).

Drain the coolant until the level is below the thermostat.

Disconnect the engine coolant temperature (ECT) sensor electrical connector and the heated oxygen sensor (HO2S) electrical connector clip from the bracket.

Reattach the radiator outlet hose to the thermostat cover and position the radiator outlet hose clamp at the thermostat cover, then fill the cooling system.

Attach a new thermostat housing to engine O-ring seal onto the thermostat housing, lightly lubricate the water feed pipe seals with coolant, and install new O-ring seals onto the water feed pipe. Insert the water feed pipe into the thermostat housing, aligning the locator tab, and seat the O-ring seal by pushing inward toward the water pump.

Reposition the radiator outlet hose clamp at the thermostat cover and remove the radiator outlet hose from the thermostat cover.