Replacing a BMW lower radiator hose seems straightforward, until the temperature sensor gets overlooked.

In this Inside the Brands episode, CRP Automotive explains a common mistake during BMW cooling system repairs that often leads to leaks and comebacks: reusing the original temperature sensor.

On many BMW models, including the E46 3 Series, E65 7 Series, E83 X3, and X5, the temperature sensor is mounted directly in the lower radiator hose. That sensor uses a small O-ring that gets crushed during initial installation. When it’s removed and reused in a new hose, it often fails to seal properly.

The result is a coolant leak that shows up after the vehicle leaves the shop, turning a routine repair into an avoidable comeback.

This video explains why reused temperature sensors leak.
How crushed O-rings cause sealing issues.
Why lower radiator hoses with pre-installed sensors help prevent comebacks.

Rein Automotive offers lower radiator hoses with temperature sensors pre-installed, eliminating the need to transfer old sensors and reducing the risk of leaks after installation.

If you work on BMW cooling systems, this is an easy detail to miss and an easy problem to prevent.