The ACDelco / GM 12658352 is the OE engine coolant bypass pipe upper seal (O-ring) — bypass pipe to lower thermostat housing — for 2017–2025 Chevrolet Silverado and GMC Sierra 2500 HD / 3500 HD with the 6.6L Duramax diesel.

Features & Benefits

• OE coolant bypass pipe upper seal / O-ring, GM P/N 12658352
• Seals the bypass pipe to the lower thermostat housing (per GM)
• GM notes it is also included with the bypass pipe
• Genuine GM / ACDelco OE part, designed, engineered and tested to GM standards and backed by General Motors

Application

• Chevrolet Silverado 2500 HD / 3500 HD and GMC Sierra 2500 HD / 3500 HD with 6.6L Duramax diesel (2017–2025)

Always verify fitment by VIN or by matching the GM/ACDelco part number on your original part before ordering.

Cross-Reference / OE Numbers

• GM: 12658352