Sunroofs: the drains that block and the water that arrives elsewhere

A sunroof frightens owners with leaks although by design it is not sealed. Water always gets underneath it, and that is normal: the only question is whether it finds a way out.

How it works

Around the sunroof runs a channel that collects water. From it emerge four drain tubes — one at each corner — running down through the body pillars and discharging under the car.

In other words: a wet channel under the sunroof is normal. A wet headlining is not.

Why they block

Leaves and pollen — the main cause, and seasonal: autumn and spring.

Dust and dirt — accumulating gradually.

Insects — building inside the tubes.

A kinked tube — after body repair or from ageing.

Pressure washing straight into the channel — it drives dirt deeper.

Signs of a blockage

Water stands in the channel after rain and does not drain.

Dripping from the headlining when cornering or braking — the water overflows the channel.

A wet pillar trim — usually the front one.

Damp under the carpet — the water runs down the pillar; covered in the water leak article.

A damp smell and misting glass with no obvious cause.

Intermittent electronic faults — the most expensive consequence: modules and connectors live in the pillars and under the seats; mechanics in the ghost codes article.

How to check

1. Open the sunroof.
2. Pour a glass of water into the channel at each corner in turn.
3. Look underneath the car — the water should emerge below, usually near the front wheels and by the rear arches.
4. Nothing emerges, or it trickles — the tube is blocked.

The check takes five minutes and is done once a season.

How to clear them

Low-pressure compressed air — carefully; high pressure blows the tube off its spigot.

A soft trimmer line — gently, without force.

Water at low pressure.

What not to do:

• Stiff wire — it punctures the tube inside the pillar, and then the water goes straight into the body. The worst case, and expensive to put right.
• High pressure — it detaches the connections.
• Chemicals — the tubes are rubber.

If it will not clear, that means removing trim, and a workshop is the better answer.

Prevention

• Clear them once a season — spring and autumn.
• Avoid parking permanently under trees, especially during leaf fall.
• Remove leaves from the channel by hand before flushing.
• Look at the channel at every wash — five seconds.

Panoramic roofs

The same mechanism, a larger area, more water. There are usually four drains too, but they carry more.

The specific point: on panoramic roofs the consequences of a blockage appear faster, because the volume of water is greater.

In short

• A sunroof is not sealed by design; water leaves through four tubes.
• A wet channel is normal; a wet headlining is not.
• The glass-of-water test at each corner takes five minutes.
• Stiff wire punctures the tube inside the pillar — the worst outcome.
• The costly consequence is not a stain on the headlining but water in connectors.

Download the app — body electronics codes are read with an ELM327 adapter over Bluetooth SPP on Android.