Symptoms
Engine slow to warm up or running cool, erratic temperature gauge, poor heater output, codes P0597, P0598 or P0599. Note that 80–95 °C can be normal on a working map-controlled thermostat.
The fix, step by step
- Drain enough coolant to drop the level below the housing, unplug the thermostat’s electrical connector, release the hoses and unbolt the housing.
- If the history is unknown, replace the radiator hose at the same time — old hoses often seal poorly at the O-ring on the new part.
- Refill with Mercedes-approved coolant and bleed the system.
- FCP Euro suggests treating it as a roughly 60,000-mile wear item.
Tools & part numbers
- Map-controlled thermostat
- radiator hose
- MB-approved coolant (genuine or Pentofrost NF)
- Torx sockets
- hose-clamp pliers
- multimeter (heater element should read about 15.2 Ω ± 1.5 Ω)
Where to buy the parts
BorgWarner thermostat kit 272 200 05 15 (M273)FCP Euro ↗Amazon ↗
Genuine Mercedes upper radiator hose 463 500 22 75 (listed 2009–2013)FCP Euro ↗Amazon ↗
Hunting a used or discontinued part? Search eBay Motors for Mercedes-Benz G 550 parts →
Rated for a competent home mechanic with a decent tool kit. Confirm torque figures, fluids and procedures against the factory service manual for your VIN, support the truck on stands rather than a jack, and work at your own risk (disclaimer). Some parts links are affiliate links, which pay us a small commission at no cost to you.