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2018 GLC 300 Oil Consumption - Is this normal? M274 Engine

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Mike T. · rep 0 · May 22, 4:18 AM · 1 replies · solved · Question

Vehicle: 2018 Mercedes-Benz GLC 300

Hello ClearTheCode community,

I own a 2018 Mercedes-Benz GLC 300 (X253) with the M274 engine, and it has about 60,000 miles on the odometer. Over the past few months, I've noticed that I'm adding about a quart of oil every 3,000-4,000 miles. There are no visible leaks on my garage floor, and no smoke from the exhaust that I can see. I'm using the recommended synthetic oil.

Is this level of oil consumption considered normal for this engine, or should I be concerned? I've heard some things about PCV valves or other common issues with the M274. What should I be looking for, and is there anything I can check myself before taking it to a shop? No check engine light is on.

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:18 AM

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Hi Mike,

Oil consumption in modern engines, including the M274 in your 2018 GLC 300, can vary. While some consumption is considered normal, adding a quart every 3,000-4,000 miles might be on the higher side for an engine with 60,000 miles, especially if it's a recent development.

Here are potential causes and steps to consider:

  1. PCV System Issues: The Positive Crankcase Ventilation (PCV) system is a common culprit for increased oil consumption in many engines, including the M274. A failing PCV valve or clogged PCV system can lead to excessive vacuum in the crankcase, drawing oil vapor into the intake manifold where it's burned. Symptoms might include a slight whistling noise from the engine or a vacuum leak sound.
  2. Valve Stem Seals: Over time, valve stem seals can harden or wear, allowing oil to seep past them into the combustion chambers. This often manifests as a puff of blue smoke on cold start-up or after idling for a while.
  3. Turbocharger Seals: If your GLC is turbocharged (which it is), worn turbocharger seals can allow oil to enter either the exhaust or intake side of the turbo, leading to consumption without external leaks.
  4. Minor Internal Leaks/Wear: Piston rings or cylinder wall wear, though less common at 60k miles, could also contribute.

What you can do:

  • Visual Inspection: Check around the PCV valve (often integrated into the valve cover) for any oil residue or signs of leaks. Also, inspect the turbocharger's intake and exhaust sides for oil presence.
  • Monitor: Continue to meticulously monitor your oil consumption. Keep a log of when you add oil and how much.

When to See a Shop: If the consumption continues or worsens, or if you notice any new symptoms like smoke, strange noises, or a check engine light (e.g., P0171 - System Too Lean, which could be related to a severe PCV issue), it's time to visit a qualified Mercedes-Benz technician. They can perform a more thorough diagnosis, including:

  • A compression and leak-down test to check engine health.
  • Inspection of the PCV system components.
  • Borescope inspection of cylinders.
  • Diagnosis of the turbocharger for seal integrity.

Addressing this early can prevent potential long-term engine issues.

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