Mill Valley Auto Repair

FLOODING INSIDE VEHICLES – How It Can Be Avoided


We see a number of cars each year in the early part of winter with water inside – sloshing around on floors, soaking the carpets and insulation, collecting in the areas of the trunk, behind the dash and under the glove box. Almost always the source of water getting inside the vehicle is backed up sunroof drains.

Contrary to what most people would assume, sunroofs (or moonroofs) are not designed to be water tight. Instead, auto manufacturers equip the frame of the sunroof with internal drains that allow rainwater to be channeled down inside the vehicle and then expelled through body plugs that are located on the underside of the chassis.

Leaves, small fragments of tree debris, dirt and silt can collect within these drains and create a blockage. Moderate rain will cause these drains to overflow and allow rainwater to accumulate inside the cabin. Heavy and persistent rain (like what we are seeing this season) will allow this issue to become dire.

Most recently we had a 2003 Audi Allroad towed in with standing water in the driver’s side foot well area. The customer noted his car was fine one day and flooded the next. The result of rainwater in this Audi was the contamination of a locking/alarm module that is located under the driver’s side seat. The repair consisted of the replacement of the whole carpet and floor insulation assembly, cleaning and reconditioning of corroded wiring harnesses, and the replacement of the flooded control module.

This is a manageable situation; one which can be avoided entirely by periodic cleaning of the sunroof and windshield cowl drains. If vehicle owners (especially those who cannot keep their cars garaged or those who park in areas with dense tree coverage) consider drain cleaning as part of routine maintenance, this risk of rainwater flooding becomes very remote. Drains should be cleaned at least twice a year – once in late fall before the rainy season starts and once again at the end of winter.

Please ask us about drain cleaning on your vehicle and we will be happy to implement this service.


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