Pinpointing Pesky Automotive Leaks

Methods of leak detection can be as basic as eyesight, or as unique as my cousin Vernon’s rag data collection methods. (See “The Sweet Taste of Antifreeze”.)

Sensory detection is not limited to eyesight. In my article “Burned Transmission Fluid Becoming More Common”, I knew the transmission fluid was burned not only because I could see the darkened color, but primarily because I was familiar with the smell of burned automatic transmission oil.

Oil, brake, hydraulic and antifreeze fluids all have a different smell when dripping on hot exhaust and other components under the hood. No book can teach you those smells; knowledge of them comes only with experience.

I have 50 years of leak detection knowledge, which began with the methods I learned from watching my father find leaks. Some of the old methods are still valid. For example, leaking coolant hoses and heater hoses are still squeezed and twisted to determine if they are leaking.

An oil leak is the most prevalent leak in an automobile. This is because there are so many “soft” points for potential oil leakage. An automobile engine is a box of metal parts, usually 150 to 200 components, rotating at 2,500 rpm at standard-duty loads.

The soft points are the seals that contain the motor oil within the “box.” A typical engine has a front and rear crankshaft seal, oil pan seal, valve cover gaskets, intake manifold gaskets, timing cover seals and many other points in which engine seals and gaskets come in contact with the internal motor oil, which is at pressure and slung around at temperatures approaching 250ºF and higher.

Motor oil leaks are generally easy to locate. They are messy, dark, and attract dust and dirt. They actually coat the engine with an insulating layer of oil, dirt and dust. Those ugly oil patches on the engine cause it to run hotter.

This leads to shorter cooling component life and fluctuating values on the engine sensors, resulting in varying fuel and timing settings calculated by the electronic control unit (ECU). Although oil leaks are easy to see, some are missed because of crowded components under the hoods of modern front-wheel drive vehicles.

The most difficult leaks to detect in a modern car are slow air-conditioning (A/C) leaks of the refrigerant (R12 or R134a). Fast leaks are usually blowouts and are easily found by adding a little refrigerant. A/C systems circulate both a gas and oil under pressures up to 400 psi. A/C system components are located in some of the most inaccessible places in a car. There are components in the dashboard behind the glovebox, between the radiator and the grill, and hoses running all over. Refrigerant leaks were once detected by simply looking for the telltale oily spots covered by dust on the A/C components.

Propane flame detection, using a low-volume propane torch with a long subinduction hose attached, is an improvement over the A/C oily spot method. The propane flame method requires the technician to place the hose in suspected leak areas, hoping to ingest enough leaking refrigerant to change the color of the flame. This wasn’t satisfactory for small leaks, and subsequently led to electronic gas sniffers.

These worked better until R134a was introduced, which necessitated a new sniffer able to detect both R12 and R134a. The flaw with sniffers is that they were so sensitive and broad in their detection abilities, that they often erroneously registered a leak when picking up some transient gas under the hood of a car. There were certain brands of cigarettes that would set off some of the sniffers I owned.

Originally and even today, water leaks are often located by sight and by squeezing the hoses. About 30 years ago I bought a pressurizer, which allows me to see the leak without having to run the engine. I loosen the radiator cap and apply about 15 psi of pressure to the cooling system. Then I can stick my hands down between the components and physically feel a leak that I cannot see.

Power steering leaks are easier to detect because the system operates under higher pressure. Turning the steering wheel at idle generates about 600 psi in the hoses. Usually a fine stream of fluid is seen leaking from the old hose, or the seals in the steering gear assemblies drip at a rapid rate.

Transmission leaks are often as hard to find as A/C leaks. Because of their location, under and to the rear of the engine, an engine oil leak will “mask” a transmission leak. The one advantage in the past has been the slightly pink color of transmission fluid. It can be spotted on the concrete or a well-placed piece of cardboard, which helps differentiate between front- and rear-transmission leaks.

Brake fluid leaks are noticed almost immediately. The fluid runs in defined areas via the brake lines, and has a distinct smell and texture. Most brake leaks are high-pressure and are easy to spot by having an assistant press the brakes while you look for leaks.

A battery leak will be detected by its noxious, unforgettable smell. This foul-smelling fluid has only one source - the battery.

Using smoke to locate leaks is a relatively new method. A smoke generator is connected to a vacuum line, intake or exhaust manifold. This smoke under low pressure detects hard-to-locate vacuum and manifold leaks. Many A/C systems use vacuum lines to open and close a car’s defrost, heater and dashboard doors. Smoke can detect many of those leaks, eliminating the need to disassemble the dashboard to visibly find what is leaking.

Not only did I mention smoke, I also mentioned mirrors. Leaks can also be detected with the use of mirrors. What I cannot observe by direct-line sight necessitates their use. I have a collection of small and large mirrors, some on pivots and some lighted, to help see leaks.

Fluorescent dyes are the newest advancement for leak detection in the automotive world. Today, an assortment of dyes can be added to the fluids previously mentioned. These are mostly Xanthene-based dyes, and have the unusual properties of glowing in ultraviolet light.

Anyone growing up in the 1960s remembers those cool black lights and their weird effect on posters. The dyes used in automotive applications glow yellow-green - the color of a dayglo green beetle, a popular fishing lure. The dyes used in automotive applications are safe, nontoxic, and can be used around potable water.

To test for leaks, add the dye to the system, then wait for a while. Shine an ultraviolet light all along the system and wow! - that bright yellow-green under a dark hood and in tight corners is easy to see. It seems to glow in the dark! And there is nothing else the color of dayglo green under the hood.

I have developed my skills using these dyes to the point where I can accurately estimate the rate of the leak. I know this is old technology to industrial and biological experts, but I am excited about it. Faster and more accurate diagnostics are the reward my customers are getting from these new dyes.

It is important to fix a leak in your car as soon as you discover it. To put it off will cost you more than fixing the leak. I recently ruined a motor because I failed to fix a water leak in my own car. Even with years of experience, I procrastinated long enough to incur an expense of several hundred dollars, by erroneously convincing myself it can wait.

Editor’s Note
In the September issue of Machinery Lubrication, the From Under the Hood article by Phil Ramsey implied that premium gasoline could result in a 10 percent increase in gas mileage. This statement was based on the author’s experience and not on scientific studies or research.