Water Leaks
Wind Noises

Basics of Water Leak Diagnosis

Understanding the Customer Complaint
Verifying Customer Complaint

The first step in diagnosing a water leak is understanding the customers complaint.  The service advisor should ask key questions like: 

a) Does it leak only while driving?
b) Does it leak only during a wash?
c) Does the vehicle leak only when parked on a certain angle?
d) Does the customer actually see the water dripping in or sitting on top of the carpets?
e) Is the heater box turned on or off?
f) Does the vehicle have any add ons?

a:)Does it leak only while driving? If so, this should lead you to think that the floor seams or wheel wells would be leaking because the road water is hitting these areas that rain would not.  This could also mean that water is leaking around the air conditioner drain or the lower header.

b:)Does it leak only during a wash? If so,:  The customer is forcing water into an area that cannot handle the pressure, like a door glass on a convertible.  Explain to the customer how to wash their car properly. 

c:)Does the vehicle leak only when parked on a certain angle? If so, duplicate the angle for testing purposes.

d:)Does the customer actually see the water dripping in or sitting on top of the carpets? If so, this narrows down the testing time.  For example, the customer may diagnose a water leak as a windshield leak when they never actually see the water dripping from the windshield.  Customers tend to assume the windshield or backlite is leaking when their floors are wet. 

e:)Is the heater box or A/C turned on or off? If on, it could be an air conditioner leak or water is being "sucked" into the air vent.  Think of the air vent as a wet and dry vacuum hose.  As it is drawing in fresh air from outside into the heater box, water could be drawn in too.  Air vents are generally positioned and covered to allow only air to enter.   If there is too much water it cannot drain from the plenum as fast as it is filling up.  Sometimes clearing any blockage of the plenum drains or making a better seal at the plenum cover above the air vent will fix this.  If the customer insists on driving through a car wash with the air conditioner on high, this complaint is not fixable.  A suggestion would be to put the setting on recycle rather than fresh so that the outside air is not being drawn into the air vent also, look for pines needles or leaves clogging the plenum.

f:)Does the vehicle have any add on's? If so, look for an improper installation of the part.  The most common is car alarms or speakers in the door panels.  The wiring may have to be re-routed so it is not going through the steering column or factory grommet.  An after market wire should have it's own hole drilled through the fire wall and properly sealed.  Other problems are screws with no screw anchors for a roof rack or sun shade.  Any screw used to hold these on should have an anchor cell or c/b wires over a door or trunk weather strip.  Most of these repairs should not be covered under factory warranty.  A diagnostic charge should apply and the repair sent back to the installer.  The installer should warrant these repairs and should reimburse the customer for the diagnostic fee.  In the case of an after market moon roof or sun roof, you run the risk of breaking a part that will be hard to replace, shoddy installation (poor workmanship) problems should be returned to the person who caused them therefore washing your hands of something that may be unrepairable.

Other variables in the diagnosis are the weather and repair history of the vehicle.   If the customer complaint is the passenger front and rear floors are wet and the weather has been hot and humid, suspect the air conditioner is the cause, not a typical water leak.  Very cold weather will cause moon roof drains to ice shut.  Check the vehicle repair history for door panel being removed.  A lot of times, if a mechanic had to change a part behind a door panel he will have created a leak by not installing the splash shield correctly.  If a windshield has been replaced you may want to find who installed it and have them warranty their repair.  If the car has been under coated, check to see if the rocker panels might have been sealed shut and won't let the water out.   Plugs in a weather strip mating surface.  If under coat is sprayed into the deck lid, they sometimes drill holes in the underside of the deck lid and these grommets deform the weather strip.

The next step in diagnosis is a visual inspection to verify the customer complaint and locate the obvious causes.  On the outside of the car check the door alignments and look for any add ons.   Inside the car, for example, if the right rear floor is wet, remove the interior trim molding and pull the carpet up in the complaint area.  Look for signs of a water leak, rust, mud, waterstains, or factory sealer skips. Start at the lowest area of the floor pan and move up to the highest. The front of the unit is the highest and the rear the lowest.


Testing is used to find the leak and verify your repair.  There are different ways to test.  Each depends on the customer complaint and from the information gathered in your visual inspection.

1. Spot water test:  Use low water pressure and start testing low in the suspected area, slowly moving the hose up until the leak starts.  This test works best with two people:  one holds the hose in place while the other is inside the vehicle looking for water.

2. Shower stand water test:  Good for all over testing to find a leak.  Drive the car up under the shower stand and look for water with a flash light.  Shower stand test works best for testing large areas like a trunk.  They are also good for simulating rain when testing T-Tops and convertibles.

3. Dent puller test:  The dent puller is a mix of both the shower stand water test and the spot test.  You can stick the dent puller close to the suspected leak and still be able to get through the door without getting the whole inside of the car wet.  You can also place the dent puller on the roof and test the whole cowl/dash/door area while you go in through the other door to check for leaks.   Putting the dent puller on the door glass is a good way to check for splash shield leaks.  Dent pullers don't work well on cars with roof rack or convertible tops.

Different Types and Causes of Water Leaks

Body leaks: 
(1) Joints, seams, pin holes, grommets, gaskets and improper or lack of factory sealer.  The latter comes into play usually at the ends of longs seams or joints where the seam bends or meets with another seam. 
(2) Caused by improper sealing of metal joints and seams,  loose grommets or sheet metal screws, harnesses, sheet metal burn or pin holes, hollow rivets, foam gaskets (tail lights or air vents), crimped gaskets, improper (over tightening)of body parts (F150 backlite).

Weather strip leaks:  (1) a) Damaged or deformed weather strips, b) Improper installation of the weather strip, c) Lack of or missing factory sealer in the weather strip flange cavity, d) Improper adjustment of components in relation to the weather strip, e) Damaged or pitted weather strip mating surfaces.  The most common is (c). (2) Improper installation, improper alignment of weather strip components (door top), damaged or deformed weather strip, irregular weather strip mating surface, or lack of factory sealer in weather strip flange cavity (this is also a body leak - gasket)

Stationary glass leaks:  skips or voids in the factory urethane sealer. Or loose bolts.

See the training section for more information on these leaks.

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