The Easiest Way to Find Out Which Part of Your Car Is Leaking
Have you ever noticed rainbow spots on your driveway after it rains? What you see is the principle of thin film interference in action and a sign that someone’s car is leaking. But before you can eliminate the root cause of the leak, you need to figure out where it comes from and what it is. One of the easiest ways to do this involves a large piece of cardboard and some detective work. I enlisted the help of two mechanics—Jason Farrell, an ASE Certified Master Technician and editor of Diary of a Mechanic , and John Lim, a mechanic and owner of JB Motor Works —who told me how to take the cardboard test and how to perform it. identify leaked liquid.
How to Use Cardboard to Find Car Leaks
While the cardboard test is fairly simple, here are a few things to know to help you get the most out of the process.
Installation
Here’s what to do:
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Park : When you’re done driving for the day, “try to park on a level surface so the liquid doesn’t drip off the cardboard,” says Lim.
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Wait : To be safe, Farrell recommends waiting for the engine to cool before starting work.
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Set aside the paper : Place a large piece of light-colored cardboard under the car. “Make sure the cardboard extends beyond the width of your car,” Lim tells me. “If possible, use a large piece that can cover the area from the front bumper to the rear.” Farrell recommends using heavy cardstock. Most people aren’t going to keep car-sized pieces of white cardboard on hand, so you may have to improvise. Could you:
– Glue several pieces of cardboard together, placing the tape on the underside only if possible.
– Glue or glue pieces of white paper on top of the cardboard.
– Use white construction paper (the kind that comes in a roll) and tape or press it around the perimeter to keep it in place.
-Use a light-colored tarp or an old sheet.
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Wait a little longer: leave everything in place overnight.
Identification
Check the cardboard (or sheet, or construction paper, etc.) the next day. “Stained cardboard tells a story,” says Farrell. More precisely, it will provide two pieces of information: what fluid is leaking and where it is leaking from.
It is usually easier to first try to determine the source of the leak while the cardboard is still in place.
“You need to trace any drips or stains on the cardboard back to the car,” explains Lim. “The position of the spot on the cardboard should give you a rough idea of where to start looking. However, keep in mind that liquids may drip from one part, land on another, and then fall to the ground, so there may not be a leak. right above the spot.”
Farrell suggests using a flashlight to illuminate the undercarriage when looking for leaks, and taking photos of the location and nature of the stains while the cardboard is still under the car and after it comes out.
Once you remove the cardboard or sheet from under the car, it’s time to take a closer look at the stains.
Liquids
“By examining stains on cardboard, their location, color, odor and consistency can help identify the source,” Farrell explains. “For example, oil stains that drip straight down are likely coming from the oil pan or filter area. Greenish fluid that accumulates near the front indicates that coolant is coming from the radiator, hoses, or water pump. “Brake fluid may eat through the cardboard, indicating a leak higher up around the calipers or brake lines.”
Here are some more tips for identifying different liquids from Farrell and Lim:
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Motor oil is usually dark brown or black in color, feels slippery, and burns your nose.
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Transmission fluid is usually red or green in color and slippery.
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The coolant may be pink, green, or yellow, feel slippery, and smell sweet.
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Power steering fluid is clear to light brown in color and has a burnt marshmallow smell.
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Brake fluid is clear to light brown in color and feels oily but not slippery.
If it looks like you have multiple leaks, Farrell recommends troubleshooting in order of difficulty. “Always start with the simplest possible leaks before digging deeper, in case it’s easy to fix,” he says. “Catching problems early by ‘reading’ that cardboard can prevent thousands of repair bills down the road.”