This week we had to fix a Mercedes-Benz that was overheating. The problem was the upper radiator hose. It turned out that a bad engine led to the radiator hose stretching too much and eventually failing.
The engine mounts on these cars are oil-filled. Around the 100k mile range, they fail. Most owners don’t even realize that they have failed engine mounts. The most common symptom of the bad engine mount is engine vibrations felt on the steering wheel or seat when the car is in Drive.
The radiator hose pulled out of the radiator due to the bad engine mount. The engine then lost most of the coolant and started to overheat.
Replacing the radiator hose is simple and takes less than 20 minutes. If you have looked at the radiator hose on Mercedes-Benz M272 and M273 engines you can see why it’s so simple.
A failed engine mount allows the engine to jump up under hard acceleration. This excessive jump pulls the upper engine house, which eventually gets damaged and will eventually pull out of the radiator.
Replacing the radiator hose is simple. Follow these instructions.
- Allow the engine to cool down then open the hood.
- Remove the air intake hose on the driver’s side.
- Remove the radiator hose by pressing the C clip and pushing it slightly out. You don’t need to remove the C clip completely. On the engine side, the hose is connected with another C clip or with a clamp. C clip is used on E-Class; for example, while on CLK550, there is a clamp.
- Connect the hose on the engine side first.
- Insert the coolant hose in the radiator port making sure it is fully inserted. Once it is inserted, press the C clip to lock the hose in place.
- Add engine coolant to bring the level between the min and max mark. You check the coolant level by looking at the marks on the expansion reservoir.
You don’t need to remove the C clip completely. On the engine side, the hose is connected with another C clip or with a clamp. C clip is used on E-Class; for example, while on CLK550, there is a clamp. 
This guide applies to most Mercedes Benz models with 350 and 550 engines, such as E550, CLK550, ML550, CLS500, E350, SL550, and many models.
We hope you find the Bad Engine Mount Leads to Engine Overheating guide helpful. Check these troubleshooting and repair guides for more help on your Mercedes-Benz.