Water Getting Into the Bus: Finding Leaks Caused by Seals and Gaskets
6 minute read · ·BAYKOÇ Technical Team
Water entering a coach is one of the most visible sources of passenger complaint; it rots seat upholstery, makes carpets mouldy, and if it reaches the wiring it causes far more expensive faults. Yet the cause is usually a weatherstrip costing a few pounds a metre. The problem is not the price of the part but the difficulty of locating the leak.
Where water gets in, in order of frequency
- Glazing rubbers — particularly the lower corners of the windscreen and side windows.
- Door weatherstrip — once hardened, it loses its closing pressure.
- Luggage bay seal — the first place to look on vehicles taking water into the bays.
- Roof vent and air-conditioning unit gaskets — the main source of water dripping from the ceiling.
- Door threshold and step rubbers.
- Aerial, horn and lamp mounting holes — the sealant may have aged.
Three practical ways to find the leak
The paper test: close the door or luggage hatch with a strip of paper trapped in the seal. If the paper pulls out easily, the seal pressure is insufficient at that point. Repeat at 20–30 cm intervals around the opening and map the weak zone.
The water test: put one person inside the vehicle and run a hose from outside at low pressure, working upwards from below. Do not use high pressure — it will push water past a perfectly good seal and send you in the wrong direction. The person inside marks where the first drop appears.
Dust trails: in dry weather, look at the inner surface in the suspect area. A line of dust and dirt shows the path air and water are taking. This method is particularly effective on vehicles with wind noise.
Mistakes made when replacing seals
- Buying the wrong cross-section. Seals are sold by profile; two that look similar deliver different closing pressure. Bring a 10 cm piece of the old seal, or send us a photo, and we will match the section.
- Not cleaning the surface. A seal bonded over old adhesive and dirt lifts within a few months. The surface must be cleaned with thinner or a suitable cleaner.
- Stretching the seal while bonding. A stretched seal recovers over time and opens up at the corners. Bond it relaxed, with a slight surplus.
- Patching with silicone. Silicone is a temporary fix, lifts paint when removed, and hides the real leak so the problem grows.
Part Categories in This Article
The parts discussed above are in stock in the following categories.
- Door, Rail, Luggage & Glass Seals (36)
- Glass & Glazing (10)
- Flooring & Mats (8)
- Chemicals & Adhesives (5)
Related Makes
Frequently Asked Questions
What most often causes water to get into a bus?
Glazing rubbers and door weatherstrips. Both harden over time and lose their closing pressure. They are inexpensive parts sold by the metre — the work is in locating the leak.
Should I use high-pressure water to test for leaks?
No. High pressure will push water past a sound seal and lead to a wrong diagnosis. Use low pressure, working upwards from below.
What do you need to supply the right seal?
Seals are sold by profile cross-section. Bring a 10 cm piece of the old seal or send a photo of its section and we will match it.
