Why does my car cooling fan run constantly after starting?
The cooling fan switches on shortly after starting the engine and runs continuously at maximum speed, even after replacing the coolant temperature sensor. Quotes indicate this affects vehicles like Mercedes models regardless of whether the air conditioning is turned on or off.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1replacing the coolant temperature sensor
- 2running with the AC off
- 3testing the fan with wooden stick test
- 4measuring with a multimeter with microfarad setting
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“The cooling fan in my Mercedes switches on 15-30s after I start the car and stays on until I turn the car off.”source ↗
“They recommended changing the coolant temperature sensor (image attached) which I just did and it didn't work.”source ↗
“Unfortunately, the fan runs at maximum speed regardless of whether the AC is on or off”source ↗
“I tested the fan with wooden stick test and is working. So the motor works but does not start. Is that definitely the capacitor? Also I have another capacitor that is not popped on the top”source ↗
“I found the AC coil fronte I cleaned all coils but the fan does not start. Is the capacitor broken?”source ↗
Where this came up
People with this problem also raised
- 5Why does my HVAC fan run continuously and blow hot air?
- 2Why does my AC compressor run continuously and never shut off?
- 3How to check if a vibrating radiator is caused by a bad fan
- 4Why does the outdoor AC fan stop while the compressor keeps running?
- 9Why does my car A/C compressor keep turning on and off?
- 13Why do cooling coils keep freezing over?