Engine overheats
Coolant temperature climbs above 100 °C in stop-and-go or up grades.
M117 cooling has a viscous fan clutch + electric auxiliary fan + 87 °C thermostat. Loss of any one component will cause overheating in traffic but may run fine on the highway.
What the diagnosis checks
- Does it only overheat in stop-and-go traffic, fine on the highway?
- Does the auxiliary electric fan run when A/C is on or coolant > 100 °C?
- Coolant level steady — no loss between checks?
Possible causes it points to
- Viscous fan clutch failed
- Auxiliary fan or temp switch
- Thermostat stuck closed
- Head gasket / external coolant leak
Parts for this job
Cooling system serviceLoading the step-by-step diagnosis…