The Wet Spot
I recently received an email from a frustrated customer attempting to track down the source of water in his truck. Thinking it was the often guilty high mount third brake light, they were wanting to make sure a purchase of my third brake light seal listed here and on Ebay would fit their truck. Additionally the wanted to see if I thought it would do the trick. My gasket would fit and according to their description of a damp spot in the headliner and water in the rear of the cab....etc, it would seem the housing seal was the likely culprit. However, according to what they were telling me, they had "tried silicone, butyl tape, a Dorman light housing and eventually a NOS Ford housing" all with no success in keeping the water at bay. Well, I certainly would like to provide the fix after all of this trouble but I suspected that the leak was at the top of the window seal, just an inch or so away from the third brake light.
I have ran in to this before. I manufacture a superior third brake light gasket for the Ranger, B series Mazdas and a few Super Dutys that should remedy a cab leak from the housing pronto. Of course despite a good installation guide with all the proper warnings and tips, some folks have either skipped a step, or worse, not diagnosed the problem correctly to begin with, which leads to problems. In this case the owner had been chasing the wrong source and selling them a new seal would have created more anxiety for them, not to mention throwing more money at the perceived problem only to be disappointed.
Water, by nature, is insidious. It enters in one area but does not show up until it is on the opposite side of your cab or shows up in the footwell but originates from high up in the firewall. It soaks, runs, creeps, evaporates and magically reappears inside your windshield as condensation. It causes fungus to sprout, creates an unmistakeable stench and eventually turns your truck in to a rusty terrarium.
While finding a leak is sometimes a nightmare, there are some things that can make life a little easier during the search.
1). Clean your cab. Getting rid of extra stuff will greatly benefit your search for a leak. If for no other reason than your own sanity. Tossing that fast food garbage, AC/DC t-shirt and $7.63 in change off your floor is a good thing. While your at it, pull your floor mats, if they are on carpet leave them out for now. Getting as much material out of the way and unable to soak up moisture, or keep in in place is a good thing. If you can thoroughly clean and dry your cab in a shop or garage out of the weather do it. Careful use of a heat source like an electric space heater for a couple of hours to get things nice and dry would be great, but-DO NOT LEAVE A HEAT SOURCE UNATTENDED FOR ANY AMOUNT OF TIME IN YOUR CAB!!! Follow the instructions on your heater, don't use anything that produces a flame, be careful......!!!
2) Toilet paper. A plumber once installed a toilet in my bathroom and left a single layer of toilet paper neatly arranged around the floor between the tile and the base of the porcelain. I learned that a single sheet of the stuff will immediately soak up and reveal even the slightest amount of seepage. This is really handy for finding a source of a leak. Use single sheets to "touch" suspected gaps. You can leave sheets in place overnight in rain to check the next day. Your neighbors will of course think you have lost your mind so just for fun, wear a shower cap and towel in your driveway as you place your sheets of "test" paper. See the Dye heading below for more on this, but TP will also reveal your test dye water.
3) A good flashlight. I have made this mistake, thinking I had good shop lights, I have searched high and low for something. Finally out of desperation I grab the flashlight and.... golly there it is! Fact is, a good flashlight will literally "light up" even a slightly damp area you may not see. You can get a decent LED light almost anywhere and they are not necessarily expensive. Harbor Freight often as a "free" LED flashlight in their coupon selection.
4) Touch. Make sure your hands are dry. Reach in, around and behind suspected sources of moisture. If in doubt of whether you have found water, rub your chosen finger with your thumb or another finger. Any tackiness would indicate you have found a damp spot. Caution is needed here since in most cases you are reaching in to areas where you cannot see, watch for sharp edges, moving parts that can bind or pinch and perhaps, obviously, any motorized windows, door locks, heater fans.....
5) Dye. Tried everything? Fluorescein, or other types of dye can be used and can be found readily online or possibly at your local hardware store. The dye has various uses, not the least of which would be mixing with water in a squirt bottle to apply around suspected leaks. With of course the warning of staining interior parts etc, you can trace the leaking source with dye as it shows up under a black light. Don't have a black light? Inexpensive flashlight versions are available in pet stores....etc. Used for finding "organic" pet stains, these work great with the dye. An inexpensive and easy to make dye can be made from a yellow high lighter, look for instructions online.
Judicious use and a bit of time can produce amazing results that may surprise you.
Of course once you find the source, sealing it is another story. But finding it is usually at least half the battle and seals are cheap compared to repairing long term damage. Keep in mind the story of my frustrated customer who had spent considerable time and money to fix his leak only to realize he was an inch away from the actual problem.
Last edited by The Mook; 12-22-2016 at 08:36 PM.