Preparing your car for the monsoon: an underbody checklist

The parts of your car that are quietly rotting

Salt, slush and grit pack into the chassis rails, the inner wheel arches and the sills. Nobody looks there, water sits there, and by the time rust shows on a visible panel it has usually been working from the inside for a season or two.

Wash it before you coat it

Anti-rust compound sprayed over caked mud seals the moisture in. The car goes on a lift, the underbody is washed at high pressure and then properly dried — only then does the rubberised compound go on the floor pan, arches and sills.

The bits people forget

Drain holes in the doors and sills block with leaf litter and then the door fills with water. Clear them. Check the boot well for damp, and replace the wiper blades before you need them rather than in the middle of a downpour.

Inside the cabin

Damp carpets in monsoon are the start of both the smell and the corrosion under the mats. If the footwell is wet, find out where it is coming from — usually a blocked AC drain or a perished door seal — before you dry it out.