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2017 S550 Coolant Leak and Low Coolant Warning

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Robert C. · rep 0 · May 22, 4:13 AM · 1 replies · solved · Question

Vehicle: 2017 Mercedes-Benz S550

Hey everyone,

I'm having an issue with my 2017 Mercedes-Benz S550 (W222) with the 4.7L V8 engine, which has about 60,000 miles. Recently, I've been getting intermittent 'Low Coolant' warnings on the dash. I've topped it off a couple of times, but the level seems to drop again after a few days of driving.

I've looked under the hood and noticed some dried coolant residue around the front of the engine, near the accessory belts. There's also a faint sweet smell when the engine is warm. I haven't seen any puddles under the car, so it seems like a slow leak that might be evaporating. I'm worried about potential overheating or damage if this isn't addressed quickly.

Has anyone with a W222 S550 experienced a similar coolant leak? What were the common failure points you found? Any advice on where to start looking would be appreciated. Thanks in advance!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:13 AM

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ClearTheCode admin answer:

A recurring 'Low Coolant' warning and visible residue with a sweet smell are clear signs of a coolant leak in your 2017 Mercedes-Benz S550. Addressing this promptly is critical, as even a slow leak can lead to overheating and severe engine damage if the coolant level drops too low.

Common Causes for Coolant Leaks in W222 S550 (M278 V8):

  • Water Pump Failure: The water pump is a common failure point, especially as vehicles age. Leaks often appear from the weep hole or around the pump housing, leading to residue near the accessory belts.
  • Thermostat Housing/Gasket: The plastic thermostat housing or its gasket can degrade and crack, causing leaks.
  • Radiator Leaks: The radiator itself can develop cracks or pinholes, particularly at the plastic end tanks, leading to slow leaks.
  • Coolant Hoses and Connections: Hoses can harden, crack, or clamps can loosen over time, especially at connection points to the engine, radiator, or heater core.
  • Expansion Tank/Cap: The coolant expansion tank can develop hairline cracks, or the cap might not be holding pressure correctly, allowing coolant to escape as steam.
  • Oil Cooler Gaskets: Less common for external leaks, but internal leaks can mix oil and coolant.

Recommended Steps:

  1. Visual Inspection (Cold Engine): With the engine cold, carefully inspect the areas where you saw residue. Pay close attention to the water pump, thermostat housing, radiator top and bottom, and all visible coolant hoses. Use a flashlight to look into tight spaces.
  2. Pressure Test (Professional): A cooling system pressure test is the most effective way to find slow leaks. A shop will pressurize the system and then look for drips or sprays. This can reveal leaks that only occur under pressure.
  3. Check for Codes: While less common for simple leaks, overheating or low coolant can trigger codes like P0117 (Engine Coolant Temperature Sensor Low) or P0118 (Engine Coolant Temperature Sensor High) if the engine's temperature regulation is affected.

When to See a Shop:

  • Immediately if the 'Low Coolant' warning becomes persistent, or if the engine temperature gauge starts to rise above normal operating range.
  • If you cannot locate the source of the leak through visual inspection.
  • For a professional cooling system pressure test, which is crucial for identifying elusive leaks.
  • If the leak appears to be from a complex area (e.g., behind the engine, under intake manifold) or if it's significant, as continued driving with a low coolant level risks severe engine damage.
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