* Intake Manifold Gasket: This is the most common culprit. The gasket seals the coolant passages between the intake manifold and the cylinder heads. Leaks often appear as weeping or dripping along the mating surface.
* Intake Manifold itself: Cracks in the intake manifold, especially near the coolant passages, can cause leaks. These are less common but possible, particularly with age or damage.
* Coolant Passages within the intake: While less accessible, internal cracks or corrosion within the intake manifold's coolant passages can leak. This is usually diagnosed by pressure testing the cooling system.
* EGR Cooler: On some 5.3L engines, the EGR cooler is located near the back of the intake manifold and can develop leaks, leading to coolant entering the intake system.
* Water pump (if very rear-facing): While less likely to manifest *directly* at the back of the intake, a severely leaking water pump could drip down and appear as if it's coming from the back of the intake.
To find the leak:
1. Thorough visual inspection: Start with a careful examination of the entire area, looking for signs of coolant residue (white, milky deposits), wetness, or dripping. A pressure test of the cooling system is essential. Pressurizing the system will often make even small leaks easier to detect.
2. Possible removal of the intake manifold: For a definitive diagnosis, removing the intake manifold might be necessary to fully inspect the gasket and coolant passages. This is a moderately involved job.
3. Pressure Testing: A cooling system pressure test is crucial to pinpoint leaks, especially those that are difficult to see visually.
Without a visual inspection, it's impossible to say with certainty where the leak originates. A mechanic with experience working on 5.3L engines will be able to diagnose and repair the leak efficiently.
