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Finding Engine Oil Leaks

header finding lights with a UV light

My first car used copious amounts of oil. Every week I checked the oil and topped it off. 

Most of this oil was lost through leaks. The car leaked like a sieve, and I couldn’t park it in anyone’s driveway. It had its own nasty spot in the street where it leaked overnight. 

One weekend, I decided to fix the leak. The challenge was identifying the source of the leak. There was oil all over the engine and transmission, making it difficult to identify the source of the leak. 

I used some rags and tried to wipe down the engine, but cleaning the engine with a few rags was a hopeless task without investing a lot of time and water. 

However, I knew I could get an engine oil leak detector kit to find the leak. So I grabbed one from Autozone on my way home one Friday night. Saturday was going to be leak detection day. 

Here is how you use a leak detection kit to find rogue leaks on your vehicle. 

What Is Required To Run A Leak Test?

  • A shaded spot
  • Fluorescent Dye
  • Protective, colored safety glasses
  • An Ultraviolet Light

I haven’t noticed a big difference in the brands on this. You can stop by your local auto parts store like O’reilly’s or Autozone (or Pep Boys if you have one of those) and grab whatever they have on hand. 

Protip: A larger UV leak detection light with 5,000 lux makes it easier to locate small leaks. I eventually upgraded to a bigger light. 

Steps To Find An Oil Leak

  1. Put the car in a shaded place
  2. Consider cleaning the engine up some to remove excessive oil
  3. Add UV dye to the oil
  4. Start the engine
  5. Examine with a UV light while wearing safety glasses. 

When searching for a leak, concentrate your search on areas that are most likely to leak. This means shining the flashlight around all of the gasket lines on the engine, the point where the engine connects to the transmission, the drain pan, and the oil filter. 

Locating Oil Leaks With A Tracing Dye

antifreeze puddle on concrete

If you don’t know where the oil leak is coming from, it is likely you will replace a gasket to only find out that the leak is originating from a different gasket. When oil is leaking, it can spray and then flow around in the engine bay, coating everything in oil and making it difficult to find the source of the leak. 

Replacing gaskets is the most expensive way to fix a leak. 

You need a better option for identifying leaks. 

The industry standard is to use an ultraviolet fluorescent leak detection dye. These dyes illuminate where the leak is coming from and make it easier to find the source of the problem. 

Testing with a fluorescent dye is easy. You add the powder to your engine oil and run the engine for a few minutes to allow it time to mix. After donning the protective safety glasses, you can use UV light in a dark room to illuminate the leak. The fluorescent leak detection dye will light up brightly, allowing you to trace the leak to where the UV dye concentration is heaviest.

I like to start looking for the leak while the engine is running. If you have an aggressive leak, the UV dye can spread quickly, making it difficult to pinpoint the source. At the same time, slow leaks might need a little more patience to find. 

UV dyes are safe to use and won’t affect the performance of your oil. This means that you can also retest with dye after the leak is repaired, and you are not required to change the oil after a dye test. You can simply wait until your following regularly scheduled oil change. 

In fact, some folks and auto shops run dye tests as a regular part of their maintenance program on high-mileage vehicles. 

Identifying Oil Leaks

Oil leaks are easy to identify. There are only about three significant leaks that a car will develop: transmission, oil, and antifreeze. Each one of them looks different. 

Engine oil is a dark, oily substance. It stains the concrete it falls on and creates dark patterns on the ground. When water is poured on it, the water rolls off with a slightly milky sheen. 

Engine oil is essential for proper engine function. Low oil can cause the engine components to rub against each other and “seize”, ruining the engine. Identifying and repairing oil leaks can prolong the engine’s life, saving money on costly repairs. 

On newer cars, even slightly low oil can cause the timing to miss or can create camshaft issues. These new model cars are not very tolerant of poor oil quality or low oil levels. 

Transmission oil is reddish. Transmission leaks are also oily but tend to be smaller leaks than engine oil leaks. You can put a napkin on the oil slick on the ground and see what color the oil is by examining the napkin. 

Antifreeze has a distinctive sweet smell and is generally green or orange. It also tends to be less oily and does not stain the ground quite as much. 

All these oils can be identified with a leak detection kit as the detection system works similarly with fluorescent powders and a UV flashlight. 

However, you first need a general idea of which fluid is leaking so you can know where to add the fluorescent powder. If you add the powder to the radiator, thinking you have an antifreeze leak, it will not illuminate an oil leak. 

Common Oil Leaks Sources

head gasket replacement

Engines have multiple parts that are bolted together on the base of the engine, also known as the “engine block.” Between each of these components is a small felt, steel, or rubber gasket designed to prevent the loss of fluids.  On high-mileage vehicles, the gaskets are apt to deteriorate and leak. Some gaskets are easy to replace, while others are harder to reach, require specialized tools, and are very costly to repair. 

One of the most common areas for engine leaks is the valve cover. The valve cover gasket is one of the easiest to repair and can often be accessed through easy-to-reach bolts on the top of the engine. If you can identify a valve cover as the source of the leak, you can save hundreds of dollars in labor costs by replacing the valve cover gasket. 

Drain pan gasket leaks are another relatively affordable repair. Since all of the drain pan bolts can be directly accessed from the underside of the vehicle, these gaskets can often be replaced at home by resourceful car owners. Generally, you want to drain the oil first and then remove each of the bolts on the drain pan to access the damaged gasket. 

Rear engine main seals are another common leak source. Unfortunately, these are much more costly to replace as the engine must be separated from the transmission as part of the repair process. This generally requires expensive equipment and a lot of highly specialized labor. While the replacement seal may cost less than $100, the labor can easily exceed $800 on an engine rear main seal replacement. 

Other leaks are more difficult to stop. For example, oil can leak from the crankshaft or camshaft seals. These types of leaks tend to be smaller and are only noticeable when the car is in operation. They also cannot be fixed without doing a complete engine rebuild. 

The head gasket is also a good one to mention. Head gasket failure can appear as an oil leak, but it more commonly fails internally, and the symptoms are an engine that overheats and a milky-colored oil as the antifreeze and engine oil mix. 

How UV Light and Fluorescent Dye Works

All lights are electromagnetic radiation with different wavelengths. Light is composed of visible light, infrared, and UV light. 

UV lights move at a shorter wavelength than visible light. It cannot be seen by the human eye. However, when Fluorescent material is exposed to UV light, it absorbs the light and reflects a brilliant, visible reflection. This phenomenon is often called UV-induced visible fluorescence. 

I’ve done a lot of leak tests on transmission leaks, antifreeze leaks, and engine oil leaks. I’ve also paid for air conditioner leak testing. Frankly, it’s one of the easiest auto tests you can run. The big challenge for a home mechanic when running a dye test is finding a dark enough place. It doesn’t need to be pitch-black, but it does help to have a shaded spot, so you aren’t working in direct sunlight. 

Leak detection dyes are compatible with all vehicles, including Ford, Chevy, Mercedes, Toyota, Honda, Hyundai, Mazda, and Subaru.

Ultraviolet Vs Violet Light

visibility of uv light spectrum

Both ultraviolet light and violet light are higher energy light sources. A higher energy light source “vibrates” faster and has shorter wavelengths. 

Violet light can be seen by the human eye, while ultraviolet light cannot be seen by the naked eye. However, all ultraviolet lights tend to produce a little bit of violet light as well. A black light will create a lot of violet light and makes a good alternative.

Both violet light and ultraviolet light can activate Fluorescent dyes. They fall in the 300-400 nanometer wavelength range. 

When shopping for a UV lamp, you can choose options including beam profile and light intensity. Ideally, you want a beam profile that concentrates the light about 1-foot to 18-inches away from the source. I also find that lights with 5,000 or more Lux tend to work better as it creates a noticeable response from the dye. 

Cleaning The Engine

If your engine is incredibly messy, you may want to clean it up a little bit before running the test. Lay some cardboard underneath it and then spray down with brake cleaner to rinse off the worst spots. It can make it easier to find the source of the leak. 

Avoid spraying brake fluid on hoses, belts, rubber parts, and electrical components. Additionally, wear gloves to minimize skin contact with it.

If the wife’s car has a leak, an $8 bottle of UV dye and a black light will let you find it.

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