MajorCommonCooling

Mercedes-Benz C-Class: M274 Electric Water Pump Impeller Separation

M274 Electric Water Pump Impeller Separation is a common cooling fault on the Mercedes-Benz C-Class on the 2014–2018 cars, and we rate it major. Putting it right costs $500 to $7,000 at New Zealand independent workshop rates. Below is what goes wrong, the symptoms to notice on a test drive, where to look, and what to ask the seller before you hand over any money. It is one of 41 documented faults on the Mercedes-Benz C-Class.

Vehicle: Mercedes-Benz C-Class
Engine: 2.0L
Years: 2014–2018
Fuel: petrol
System: Cooling

This page covers the Mercedes-Benz C-Class as a model. Some faults only affect particular engines or build years — enter a plate below to narrow the list to one car.

All Mercedes-Benz C-Class faults41 documented faults on this model

What you are looking at

No photograph available

We do not hold a verified photograph of the Water pump yet. We would rather show none than show a picture of a different part.

What goes wrong

The M274 uses an electric water pump (OEM part 2742000207) with a plastic impeller that is known to delaminate and separate from the motor shaft, stopping coolant circulation without disabling the pump motor. The failure is insidious because the pump continues to draw electrical power and show no immediate fault code while the engine rapidly overheats. If the overheat event is not caught within minutes, head gasket failure and a warped cylinder head are the typical secondary outcomes.

What you would notice

Temperature gauge rising rapidly toward maximum with little warning
Cabin heater blowing cold air despite engine being fully warm
Low coolant warning light or engine temperature warning on the instrument cluster
Steam from the engine bay in an advanced overheating event
After an overheating episode: rough idle, white exhaust smoke, or coolant contamination in engine oil

How to check it

Where to look. Electric water pump mounted on the front of the engine block

Check the coolant level and inspect the reservoir for discolouration or low level indicating prior loss.
Ask whether the temperature gauge has ever reached the red zone or a warning appeared.
Have a workshop measure coolant flow rate and physically inspect the pump impeller.
Review the service history for any cooling system work.
A functioning heater core (full heat from vents when engine is warm) is a basic confirmation of adequate coolant flow.

Parts involved: Water pump.

What it costs to put right

$500 to $7,000 at New Zealand independent workshop rates. That is for this job on its own, not for the car.

An estimate, in NZD, for the repair as normally carried out. What a specific car costs depends on which part has failed and what it damaged on the way — treat this as the floor for a negotiation, not a quote.

Ask the seller

“Has the electric water pump ever been replaced? If so, was an OEM or aftermarket unit fitted?”
“Has the car ever overheated or shown a temperature warning? What was done to resolve it?”
“Is there a cooling system service record showing the coolant was changed on schedule?”

Now check the Mercedes-Benz C-Class you are actually looking at

Everything above is true of the model, and it is free. What it does not tell you is whether THIS car has been looked after: its odometer history and whether the reading has ever gone backwards, whether there is still money owing on it, whether it has been reported stolen, how many owners it has had and what it is really worth today. That comes from the official records for that plate. Enter the plate for the free details, or get the full history and a market valuation from $13.49.

Not sure what you would be paying for? See what a full KickTyres check includes.

Where this comes from

The failure described above is documented in published sources — owner forums, technical service bulletins, recall notices and workshop write-ups — held in our fault database. The inspection instructions and the cost estimate are KickTyres’ own interpretation of them, and it is a starting point for an inspection rather than a manufacturer statement.

Mercedes-Benz C-Class buyer questions

Is m274 electric water pump impeller separation serious on a Mercedes-Benz C-Class?

We rate it major and common on the Mercedes-Benz C-Class. The M274 uses an electric water pump (OEM part 2742000207) with a plastic impeller that is known to delaminate and separate from the motor shaft, stopping coolant circulation without disabling the pump motor. The failure is insidious because the pump continues to draw electrical power and show no immediate fault code while the engine rapidly overheats. If the overheat event is not caught within minutes, head gasket failure and a warped cylinder head are the typical secondary outcomes.

How much does it cost to fix on a Mercedes-Benz C-Class?

$500 to $7,000 at New Zealand independent workshop rates. That figure is for this job on its own. A car showing the symptoms on this page is usually worth either walking away from or negotiating down by at least the repair figure.

Which Mercedes-Benz C-Class years are affected?

Our research records this fault on the 2014–2018 Mercedes-Benz C-Class. Build dates move around, especially on imported cars, so treat the range as the years to look hardest at rather than a guarantee either way. The official records tell you the exact build and first registration date for the car in front of you.

How do I check for it before I buy?

Check the coolant level and inspect the reservoir for discolouration or low level indicating prior loss. Ask whether the temperature gauge has ever reached the red zone or a warning appeared. Have a workshop measure coolant flow rate and physically inspect the pump impeller. Review the service history for any cooling system work. A functioning heater core (full heat from vents when engine is warm) is a basic confirmation of adequate coolant flow. Look here: Electric water pump mounted on the front of the engine block