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Excessive Oil Consumption on my 2017 C300 - Is this normal?

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Chris P. · rep 0 · May 22, 4:21 AM · 1 replies · solved · Question

Vehicle: 2017 Mercedes-Benz C300

Hey everyone, I'm a bit concerned about my 2017 Mercedes-Benz C300 (W205 chassis). It's got the M274 2.0L turbo engine. Lately, I've noticed I'm adding a quart of oil every 1,500-2,000 miles. There are no visible leaks, and no smoke from the exhaust that I can see.

I've read online about some M274 engines having issues with cracked pistons leading to high oil consumption. Is this a known problem for my model year? What should I be looking for, and what are my options if this is indeed the case?

My car has about 75,000 miles on it, and I've been diligent with oil changes using approved Mercedes-Benz oil. Any advice or shared experiences would be greatly appreciated!

✓ Accepted solution

ClearTheCode Admin

ClearTheCode Team · rep 0 · May 22, 4:21 AM

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ClearTheCode admin answer:

It's concerning to hear about high oil consumption on your 2017 C300. While some oil consumption is normal for turbocharged engines, adding a quart every 1,500-2,000 miles is generally considered excessive and points to an underlying issue, especially with the M274 engine.

Common Causes for Excessive Oil Consumption in M274 Engines:

  1. Cracked Pistons: This is a well-documented issue for early M274 engines, particularly in 2015-2017 C300 and GLC300 models. The piston design can be prone to cracking, leading to oil entering the combustion chamber. This often manifests as misfires (check engine light with codes like P0301-P0304), rough idle, and increased oil consumption.
  2. PCV System Malfunction: A faulty Positive Crankcase Ventilation (PCV) valve or system can lead to increased crankcase pressure, forcing oil past piston rings or valve seals. This is a less severe but still common cause.
  3. Turbocharger Seal Failure: Worn seals within the turbocharger can allow oil to leak into the intake or exhaust system, leading to consumption and sometimes blue smoke from the exhaust, especially on acceleration.

When to See a Shop:

It's highly recommended to have your vehicle inspected by a qualified Mercedes-Benz specialist as soon as possible. Here's what they should do:

  1. Diagnostic Scan: Check for any stored fault codes, especially misfire codes (P030X) or lean condition codes (P0171/P0174) which can be secondary symptoms of piston issues.
  2. Compression and Leak-Down Test: These tests are crucial for diagnosing internal engine problems like cracked pistons or worn piston rings. Low compression or high leak-down in one or more cylinders is a strong indicator.
  3. Borescope Inspection: A technician can use a borescope to visually inspect the piston crowns and cylinder walls through the spark plug holes for signs of cracking or damage.
  4. PCV System Check: Inspect the PCV valve and associated hoses for blockages or failures.
  5. Turbocharger Inspection: Check for excessive shaft play or oil residue in the turbocharger's intake and exhaust sides.

Addressing this issue promptly is important to prevent further engine damage. Be prepared for potentially significant repair costs if it's a cracked piston, though Mercedes-Benz has sometimes offered goodwill assistance for this known issue, even out of warranty, depending on service history.

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