A safety cap (10), for a motor vehicle fluid reservoir (14), is configured to be attached and fixed to a neck (12) of the reservoir. The cap includes a screwing cover (16) with a first screw thread (16ba), and a safety cell (18) configured to allow passage of gas between the interior and the exterior of the reservoir, when the cap is fixed to the neck and when a pressure difference between the interior and the exterior of the reservoir is greater or less than at least one predetermined threshold value. The cap includes a ring (20) with structure (30, 30a, 32) for fixing to the neck and a second screw thread (22) to cooperate with the first screw thread. The cell is at least partly housed in the neck and surrounded by the cover and/or the ring when the cap is fixed on the neck.

Sensors are provided in reservoirs on internal combustion engines, and other applications, in which the reservoir is subjected to variations in pressure and temperature that cause the reservoir to exert variable forces on the sensor, thereby affecting sensor accuracy. To overcome problems in the prior art, a reservoir and sensor cartridge system are disclosing having: a reservoir with first and second openings, a cap coupled to the first opening, and a sensor cartridge disposed in the second opening. The sensor cartridge includes a sensor disposed in a body, a circumferential indentation formed in an outer surface of the body, a seal disposed in the indentation, and a retention feature provided on the body's outer surface. The circumferential indentation with the seal is axially displaced along the body from the sensor.

Sensors are provided in reservoirs on internal combustion engines, and other applications, in which the reservoir is subjected to variations in pressure and temperature that cause the reservoir to exert variable forces on the sensor, thereby affecting sensor accuracy. To overcome problems in the prior art, a reservoir and sensor cartridge system are disclosing having: a reservoir with first and second openings, a cap coupled to the first opening, and a sensor cartridge disposed in the second opening. The sensor cartridge includes a sensor disposed in a body, a circumferential indentation formed in an outer surface of the body, a seal disposed in the indentation, and a retention feature provided on the body's outer surface. The circumferential indentation with the seal is axially displaced along the body from the sensor.