Reasons for Antifreeze Leak in a 2003 Chevy Silverado

by Kenneth V. Oster
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General Motors vehicles such as the 2003 Chevy Silverado use DEX-COOL antifreeze, specification number GM6277M. Since the antifreeze in your vehicle is expected to provide several years of service, it is important to have your engine's cooling system components checked for leaks every time you have the oil changed. Leaks can develop on several components including the radiator, water pump, hoses, heater core and radiator cap.

Radiator Leaks

One of the the largest components in the cooling system on your Chevy Silverado is the radiator. Radiators are constructed of aluminum and plastic and are exposed to significant stress from the thousands of heating and cooling cycles an engine goes through each year. Additionally, radiators are subject to significant impact shock each time you hit a bad spot in the road. Inspection of your radiator should include checking for leaks at seams, hose connections, cooling fins and drain petcock. One final inspection point is to check the mounting brackets for damage.

Heater Core Leaks

The heater core on your Chevy Silverado looks much like a small radiator, and is located under your dash up behind the glove box. Hot antifreeze from the water pump flows through heater hoses and passes through the heater core on the way back to the radiator. Leaks can develop in the two heater hoses, hot water valve and heater core. Heater core leaks are usually discovered when antifreeze drips down onto your front passenger floorboard and makes a sticky mess in the carpet.

Cylinder Head Leaks

Head gaskets placed between the cylinder heads and engine block ensure antifreeze flows through the correct passages sealing antifreeze out of the cylinders. Over time, head gaskets can break down, causing leaks that enter the cylinders or appear on the side of the block. Some 5.3 liter and 4.8 liter Vortec engines manufactured from 2001 to 2006 may develop cracks around the center head bolts. These cracks are hard to detect because they are under the valve covers. If leaks around these cracks continue undetected engine failure may result.

Intake Gasket Leaks

Another antifreeze leak on some Chevy Vortec engines is the gasket that connects the lower intake manifold to the cylinder heads. The original gasket material is susceptible to failure and must be replaced with gaskets made of more durable materials. An intake manifold gasket failure will allow antifreeze into cylinders and may cause a vacuum leak that affects idle speed. If your engine has a two-piece intake manifold, it is a good idea to replace the upper intake manifold gasket at the same time you replace the lower gasket.

Hose and Radiator Cap Leaks

As radiator hoses age, they harden and crack causing them to leak at joints and stress points. Radiator hoses that come in contact with hot engine components will melt through and leak. If engine or transmission oil is spilled on your hoses, they can soften and leak. Radiator caps are designed to release fluid back into the reserve tank at a predetermined pressure. The radiator cap gasket can deteriorate through age, causing a leak that runs down the side of your Chevy's radiator.

Water Pump Leaks

Water pumps develop leaks at the gasket, develop leaks at the weep hole on the bottom of the pump and at the center bearing shaft. Heater hoses and a bypass hose attached to the pump and may leak due to hardening and cracking. General Motors Technical Service Bulletin 06-06-01-019B dated June 6, 2007, describes a leak on heads manufactured with a Castech logo. These heads may develop a leak that can be misdiagnosed as a water pump leak. Technician must follow procedures in the TSB to properly diagnose the leak.

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