Instructables
December might not be the best time of the year to discover that there is water inside your car, especially when you live upstate New York... and your car is staying on an open air parking lot!

I waited for a snowless day, with temperature above freezing to venture taking a look at the problem. Water was accumulating under the front passenger seat, under the rug, threatening to turn the car into a mobile swamp. To find a leak, your only option is to spray every corner of the car with water and patiently observe and listen where the dripping comes from. It turned out that the water was coming from the trunk.

Under the rug in the trunk, both the spare wheel and the jack compartments were completely underwater. Driving the car was enough to jiggle the water under the back seat. Water would accumulate under the passerger front seat, due to gravity.

Step 1: Drying and testing

Since the water, was entirely on the passenger side, the leak had to be on that side too. I started by drying all the water inside the trunks. I had to take the rugs, the spare wheel and the jack out of the car. I needed something to scoop the the water out and had an empty bottle of shampoo with the top cut, slim enough to get the water stuck inside narrow compartments. I got as much water as I could like that and finished drying things with an old bath towel. Once everything is dry, it's much easier to see where water comes from!

The procedure is to spray the, beforehand closed (!!), trunk with the water from the pitcher. Get someone in the car, the back seat pulled down, with a flashlight to listen and watch where the water comes from (I managed to both spraying and spying). The picture shows what I saw: the water was coming from the backlight!
 
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97 GRAND AM-DRIVERS FLOOR BOARDS LEAK IN FRONT & BACK FLOOR BOARDS????

WHEN IT RAINS MY DRIVERS SIDE FRONT & BACK FLOOR BOARD IS SOAKEN WET AS IT HAS AN AWEFUL LEAK "some where" & I HAVE CHRONIC ILLNESSES & AM NOT SUPOSE TO BE AROUND THE MELDEW, I'VE LEFT MY WINDOWS CRACKED TO HELP SOME, BUT LEARNED THAT ABIT TO LATE, GRRRR AT ME.... I'M ON LOW INCOME & I'M ON A FIXED INCOME & SO TrYiNg TO FIGURE OUT AWAY TO MAKE ALL FALL INTO PLACE IS IMPOSSIBLE & IS SO DEEPLY NEEDED... CAN YOU "PLEASE" HELP GUIDE ME WITH ANY SUGGESTIONS/HELP PLEASE? APPRECIATE YOUR TIME & UNDERSTANDING... ANYONE ELSE HAVE A GRAND AM"BRIGHTEST BLESSINGS ALWAYS"...
91Cavalier2 years ago
Any suggestions on a 91 Chevy Cavalier? There always seems to be water buildup behind the drivers seat. As far as I've seen going through the exterior body, "no obvious indicators" which would lead someone to believe there would be a leak on the inside. Any assistance would be great! Thanks in advance.
mole13 years ago
Thank you!! I've never understood HOW one was supposed to look for leaks before.

I used a shop vac to get water out of the trunk of our '90 Camry today. I have no idea where the water is coming from, but if it isn't freezing or raining tomorrow, I hope to try your method. (Aren't those wells supposed to drain somehow?)

[Just in case anyone else has a similar problem... we had enough water to float a piece of 2x4 on the driver's side of an '85 Tercel for years. I used the bathtub stuff everywhere I could think of. It turned out that the flimsy sheet of plastic (lack thereof) inside the front door was the problem. It didn't look important, and it got torn up when fixing the window after a break in. ]
cmorgan454 years ago
 im experiencing the same exact problem with my 2003 mazda protege es and im so grateful i found this. i just applied the caulk to my car and im currently waiting on it to set-up i was wondering how well this actually worked for you and if you currently have any problems with this also does your car leak on the passenger side floor board in the front? if so please tell me what you did to fix that. 
legazier (author)  cmorgan454 years ago
What a surprise, to read feedback more than two years after this instructable was first posted! This one leak was responsible for all the water I had in the car. The fix proposed here with the caulk actually worked out pretty well: two years later, I am still driving the same car, and have never found any water anywhere in the car... so give that a shot and let us know how that works for you.
Cheers!

 thanks so much ive tried this out and im still curently waiting on it to fully cure but so far its dry and the car has gotten wet so im guessing its fixed. thanks for posting this i kinda got lucky you have the excat car i do and the exact same problem so it was easy to find and fix. im beginning to think that that defect is a major design flaw in mazda's part because ive seen alot of forums on this exact problem for the protege. 
Solderguy6 years ago
The gel won't stop the rusting if it managed to get past the car paint. The best way to get rid of it is to buy a can of spray the same color as your car interior paint, scrape the rusted paint off, and apply the can of paint in thin layers on afflicted areas.
hondagofast6 years ago
The trunk of my car looks like that... I have no idea where the leaks are...
Smart, great pictures by the way!
natnie6 years ago
Cool. My sister's car gets puddles in the front seats and we have no idea where it's coming from. We'll try this method out! Thanks!
Patrik6 years ago
Great detective work, and some nice pictures!