Thermostat M256 for Mercedes-Benz

OE spec engine thermostat assembly, engineered for Mercedes Benz vehicles with the M256 3.0L inline-6 petrol engine. Restores correct warm-up time and stable operating temperature, helps protect against overheating and poor heater performance. Sold per unit, variant specific as supplied with housing and sensor where applicable.

What this is / isn’t:
Included: 1× thermostat assembly

Important: Match by VIN and engine code M256. Some models use different housings, outlet angles or electrical connectors. Cars with 48V EQ Boost and AMG 53 variants may use a specific spec. Always confirm by OE part number.

Key Features:

• Precise temperature control: OE-matched opening temp and flow to stabilise engine and cabin heat.

• Integrated housing and seal: Direct bolt-on replacement to reduce leaks and comeback repairs.

• Correct sensor/actuator logic: Works with the ECU for accurate warm-up and efficiency.

• Durable materials: High-temp plastics and seals resist glycol and heat-cycling.

• Exact fitment: Factory mounting points for a no-mod install.

Compatibility:
Vehicles equipped with the M256 3.0T inline-6, including, match by VIN/OE:

• E-Class W213, E450 / AMG E53

• CLS C257, CLS450 / AMG CLS53

• S-Class W222 (late) / W223 (early trims), S450 / S500 where fitted with M256

• GLE W167 / C167, GLE450 / AMG GLE53

• GLS X167, GLS450 / AMG GLS53

• G-Class W463 (select markets) with M256 petrol
  Drivetrain: 2WD and 4MATIC where applicable.

Options, engine/sensor variations:

• Standard M256 thermostat → conventional electronic-assisted stat with housing.

• AMG 53 application → verify actuator and connector style, may differ.

• Model year changes → later vehicles can use revised housings, match by VIN.

Typical OE reference families, guide only:
A256-200-… / A256-203-… / supersessions vary by model year and market.
Always order by the exact OE part number on your vehicle or confirm via VIN.

Symptoms of a faulty thermostat:

• Slow warm-up, temperature gauge stays low or fluctuates.

• Overheating under load or at idle.

• Weak cabin heat, fault code P0128 or related temperature errors.

• Coolant loss around housing, visible crusting or seepage.

Installation notes, pro tips:

• Work only on a cold engine. Drain enough coolant to sit below housing level.

• Replace the seal/O-ring, clean mating surfaces, torque bolts evenly to spec.

• Refill with Mercedes-approved coolant, MB 325.x spec, and bleed the system properly.

• Check hose routing and clamps, clear stored codes after a road test.

• Inspect adjacent components, pump, belt, radiator, for wear or leaks.

What’s included / not included:
✅ 1× Thermostat assembly with housing and seal, sensor/actuator if supplied
❌ Coolant, hoses, clamps, water pump, radiator, extra sensors, hardware

Q&A
Q1: How do I confirm I have the M256 engine?
Check your VIN data card or engine cover, M256 is the 3.0L inline-6 turbo with 48V EQ Boost on many models. Your VIN will confirm the correct part.
Q2: Do I need coding after replacement?
No coding is usually required. Clear any stored fault codes and verify operating temperature.
Q3: Which coolant should I use?
Use Mercedes-approved coolant meeting MB 325.x spec, mixed to the correct ratio.
Q4: Should I change anything else at the same time?
Inspect hoses and clamps, consider a fresh coolant service and new seal if not included.

Why choose TOParts:
OE grade engine components for Mercedes Benz with precise fitment, correct specs and long-term reliability, trusted by panel shops and independent Mercedes specialists across South Africa.