Some 2023-2025 Colorado, Silverado 1500, Canyon and Sierra 1500 trucks equipped with the 2.7L engine (RPO L3B, L2R) may have poor heater performance due to blocked coolant flow.
The coolant flow condition may be the result of an improperly positioned or twisted coolant hose, or an incomplete machining process in the heater core feed pipe port.
Coolant Hose
A kinked or twisted coolant hose on the 2.7L engine on some 2023-2025 Silverado 1500 and Sierra 1500 models may restrict coolant flow through the heater core.
If there is poor heater performance, inspect all coolant hoses for proper positioning. (Fig. 3)
Fig. 3
During inspection, it will be necessary to reposition the mesh covering on the coolant hoses in order to properly check the entire hose. In some cases, the hose may have twisted during installation, causing a kink approximately 2 inches above the hose clamp, which is covered by the mesh and is not visible. (Fig. 4)
Fig. 4
Refer to #PIT6329 for more information about the twisted hose condition.
Heater Core Feed Pipe
If there are not any twisted or kinked hoses found, another known area that may have impeded coolant flow is at the exhaust manifold outlet pipe T fitting on some 2023-2025 Colorado, Silverado 1500, Canyon and Sierra 1500 trucks equipped with the 2.7L engine.
With the engine at operating temperature, check the temperature of the heater core feed pipe. If the coolant feed pipe is not near operating temperature, there may be an incomplete machining process where the pipe connects to the exhaust manifold coolant outlet pipe. (Fig. 5)
Fig. 5
Once the engine cools down, disconnect the heater core coolant feed pipe at the exhaust manifold outlet pipe and inspect the outlet pipe spigot connection for any blockage. If there is blockage from an incomplete machining process, replace the exhaust manifold coolant outlet pipe.
Refer to #PIP5982 for more details.
– Thanks to Dave MacGillis
what a terrible picture