Find a suitable location (slightly below the low level mark on a flat surface).
The probe should never be installed in an area of cooling water turbulence.
Drill a hole of 24mm diameter using a hole saw (a cone drill is not suitable).
Remove/clean holes of burrs & sharp edges.
Use grease or a mild lubricating oil between the flat surface of the grommet until it is properly secured (if necessary turn it another ½ turn using a spanner).