Which parts fail
Components named in complaints (engine, cooling system, oil leaks, timing chain, exhaust).
Mileage when the problem started
Owner reports
Selected complaints filed with NHTSA by 2018 Mercedes-Benz C300 owners, lightly cleaned up (personal details are redacted by NHTSA).
The contact owns a 2018 Mercedes-Benz C300. The contact stated while driving 35 MPH, there was white smoke coming from exhaust. The contact stated that the check engine warning light illuminated. The contact stated that after turning off the vehicle the smoke cleared. The vehicle was towed to dealer but was not diagnosed or repaired. The manufacturer was notified of the failure. The approximate failure mileage was 54,000.
CYLINDER 1 SPARK PLUGS IS DAMAGED DUE TO PISTON DAMAGE, HOLE IN PISTON. IF EXTRA DAMAGE IS FOUND ON TEAR DOWN, COMPLETE ENGINE REPLACEMENT. This is direct from the repair facilities reports. While driving my 2018 C-300 there was smoking out of tail pipe, a rough vibration, hard to control the vehicle and it was starting to lose power. Not a good situation, had to pull over and have vehicle towed to the dealership. Worst part is this is a vehicle used to transport my 5 children to and from school and activities. My 16 year old also drives this vehicle, had he been driving this with this happening to him, the outcome could have been catastrophic. Vehicle has been inspected by 2 facilities; first was a certified Mercedes Benz repair facility and the second was the service dept. of the Mercedes Benz dealership I have serviced at for over 10 years. …
The day after I purchased my c300, the engine light popped on. I went back to dealer and they said it was a recall because of a crank case (PCV). I was upset because they never said anything about it. This was April of 2024. Note:(This Dealer was not Ray Catina's of Edison). I went to Ray Catina's in Edison for them to inspect car and I have been calling because I was told it was a national recall and it was on back order and should be here in June. It is now almost August and I called on the 23rd of July and received a call from Ray Catena on the 24th for them to tell me that "they were told that the new plan from Mercedes is to bring my car in and they will clear code. That's what they are told to do." To me, this is NOT fixing the issue. …
initial observation started happening intermittently a week before the car become inoperable. When the vehicle came to a stop like at a light the engine would sound like it was going to almost turn off like a rattle noise and a popping sound or like I hit a plastic bag sound on acceleration. Then the day it broke down I was merging onto interstate 15 I heard the same popping sound, the engine light came on and my car broke down. My car was towed to Mercedes Benz of Ontario and inspected by technicians there and by the claims inspector for safe guard international (service protection plan i purchased with the vehicle)I was told it needed an entire new engine due to cracks in two pistons, etc. This was confirmed by the claims inspector with safe guard. This car was well maintained and only had 69,000 miles on it. …
at 67000 miles the check engine light came on and is was engine code p052e crankcase ventilation regulator valve failure. This failure will cause the ending to exhaust increased contaniments in to the air. This is a know problem by MBUSA and they have changed the part design on new vehicles , this problems comes up right after the cars warranty and they cost to repair is in excess of $2500. For this to be an emission know problem by MBUSA a recall should be issued and this problem corrected under the recall process of the NHTSA ASAP. This has been reported to MBUSA and they have been zero help in this matter. The NHTSA is here to protect our citizens and environment and hopefully you will continue to do so.
The engine light is on with only 35000 miles. Upon using an OBD2 scanner, error code P052e positive crankcase ventilation(PCV) malfunction was detected. It's a problem that I researched and noticed a lot of people having the same issue. I was told that this can cause the car to stall or shut down? This causes serious risk and safety issues to drivers, passengers, and pedestrians. With so many complains about this problem, I believe the manufacturer and dealers should take responsibility before tragedies happen.
CRACKED PISTON AT 68K MILES The vehicle is very well maintained, only 68k miles, has had every oil change, only takes premium gas. I was driving it when the check engine light went on and the vehicle began shaking violently. After towing the vehicle to the Mercedes Benz dealership, they informed me that the piston cracked and they could not articulate a reason why this would happen.
Check engine light comes on, Error Code P052E, after a lot of research, this is a known defective part by Benz. Huge safety issue not addressed by them. Very costly to fix for a customer. There is a new and improved replacement part from Benz indicating they are aware of the faulty old parts that are currently in those cars but yet they have failed to do a recall.
2018 Mercedes C300. P052E check engine code. Positive Crankcase Ventilation failed with less than 28K miles. Common reported problem but not covered after warranty period, even with extended warranty addition. It's a major part of the engine function and 6 hours of labor to replace. Mercedes Benz should cover this type of fault on the design.
My c300 2018 only has 50k and suddenly the engine light is on, when I check it shows that I need the Positive Crankcase ventilation valve replaced. it cost $2300. As I know a lot of people who own Mercedes have the same problem. Three mechanics claim it on almost all C, CLA, and GLA models. Please make Mercedes recall it finally.
Engine complaints in other C300 years
Frequently asked questions
How common are engine problems on the 2018 Mercedes-Benz C300?
NHTSA has 37 complaints about the engine & cooling of the 2018 Mercedes-Benz C300, 33% of the model year's 111 complaints. The component named most often is exhaust system (1 mentions).
Is there a recall for 2018 Mercedes-Benz C300 engine problems?
No. NHTSA lists no engine & cooling recall for the 2018 Mercedes-Benz C300, though it has 18 recalls for other components. If the problem is widespread, a repair may still be covered by an extended warranty or a manufacturer service bulletin — ask a dealer.
At what mileage do 2018 Mercedes-Benz C300 engine problems start?
Half of the complaints with a recorded mileage happened before about 54,000 miles, and 50% before 25,000 miles.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.