Why You Should Test Your Car’s Fluids

Car fluids protect, clean, lubricate and absorb the vibration of thousands of moving parts. Testing the condition of all these fluids can ensure years of trouble-free driving, instead of expensive repairs or inconvenient breakdowns.

In my 50 years as a professional automotive technician and vocational educator, my best advice went beyond checking fluid levels and changing fluids at required intervals (sooner when driving in harsh conditions). You should also examine fluids to see what they’re telling you about your car.

During my career I’ve seen degraded motor oil cause a $4,500 engine failure; depleted coolant result in an $3,800 repair; and contaminated brake fluid rotting out a brake line, causing a serious accident.

Pro tip: Any fluid containing silvery or copper-colored metal dust indicates a part in that system is failing and should be immediately inspected.

About the Experts

Mr. “G” (Jerry) Truglia is one of the foremost automotive diagnostic technicians and trainers in the country. A Golden Wrench Award winner from the Trucking Association of New York (TANY) Safety Council, he achieved National Institute for Automotive Service Excellence (ASE) certification and is one of 1,900 people certified by the ASE as a world-class technician.

Ron Schornstein is the president and CEO of Acustrip in Denville, New Jersey. Acustrip produces fluid testing products and devices for the transportation industry and home use.

Testing Automotive Fluids

Here are a few ways you can test the condition of your vehicle’s fluids:

Fluid test strips

You can check the condition of your fluids while checking levels. The easiest and most thorough way is with fluid test strips.

For coolant, power steering and brake fluid, dip the test strip into the fluid reservoir. If the reservoir is in some out-of-the-way place, dip the strip using needle-nose pliers or long kitchen tweezers. Let motor oil or automatic transmission fluid drip from the dipstick onto the strip.

Schornstein says unseen contamination in any of our vehicle’s fluids can quickly cause a premature failure of that part and others as well.

For example, coolant having low pH (very acidic) can cause an automatic transmission cooler (located in the radiator) to rot. Coolant mixing with the automatic transmission fluid will ruin anything inside a transmission made from steel, cast iron, copper, plastic or rubber, as well as destroy all rubber coolant hoses.

Truglia says color alone is not enough to tell if fluids are still good. He says that automotive base fluids rarely go bad. It’s the “additive package depletion” that leaves parts vulnerable to excess wear and tear.

Test strips (Trulia calls them “predictive maintenance”) can determine if a fluid only needs to be drained and replaced with new fluid, or if the protective additives have broken down and the system needs flushing to remove corrosion or gunk before refilling.

White paper towel test

Using a clean white paper towel to evaluate fluid color can identify if they’re simply dirty and only need changing. Fluid containing “floaters” should be examined by your mechanic to determine if the system needs to be flushed, serviced or repaired.

Hydrometer or refractometer

An inexpensive coolant or battery hydrometer (some come as one unit) or a refractometer can measure anti-freeze protection, as well as battery fluid condition.

Testing Fluids

It’s best to leave manual transmission, differential and four-wheel drive transfer case fluids to the pros. Others you can test yourself.

If using test strips, wait the recommended amount of time before matching the distinct colors on the strip pads to the supplied color chart. That way, you’ll know if your car’s fluids are doing their job.

Different test strips can analyze different fluids by measuring the amounts of different contaminants. Always follow the manufacturer’s instructions and safety information.

Coolant

Coolant, a 50/50 mix of water and antifreeze, comes in various colors. It circulates throughout the cooling system and engine to maintain optimum operating temperature.

Once the additives, corrosion inhibitors and lubricating properties that protect your engine deteriorate, it leads to engine overheating and poor heater output.

Here’s what these test stripes analyze:

• Glycol concentration: Determines freeze and boil over points.
• Nitrite and molybdate: Corrosion protection additive levels that protect engine cylinder liners and other engine parts from pitting, corrosion and excess wear.
• Hydrocarbons: Detects unacceptable levels of gasoline, engine oil or even a blown head gasket.
• Potential of hydrogen (ph): High pH levels in coolant can cause scaling and corrosion. Low pH levels can cause clogging deposit buildup in the radiator or heater core, as well as bubbles forming, resulting in high pressure shockwaves that can damage the intake manifold or water pump.

Brake fluid

Ranging in color from clear to a yellowish light brown, brake fluid is hygroscopic, which means it absorbs moisture from the air even in a tightly sealed system. Moisture contaminates the fluid, causing brake components to rust, deteriorate and fail.

Here’s what these test stripes analyze:

• Moisture 1: High moisture levels cause metal brake parts to rust and corrode from the inside out, and rubber and composite parts to swell, deteriorate and weaken.
• Moisture 2: Elevated moisture levels also cause gas bubbles to form. These compress when pressing on the brake pedal, causing brake fade (the pedal feeling mushy) and greatly increasing stopping distances.
• The pH: High or low pH levels affect brake fluid’s ability to inhibit corrosion, prevent particle buildup and maintain safe braking temperature.

Pro tip: Clutch fluid is the same as brake fluid and should be checked the same way.

Motor oil

Yellowish to light brown motor oil is an engine’s lifeblood. It protects engine parts from wear by holding sludge, harsh chemicals, contaminates and abrasive particles in suspension.

Here’s what these test stripes analyze:

• Hydrocarbons: Detects unacceptable levels of gasoline or ethanol that “washes” away motor oil’s protective film, or helps diagnose a blown head gasket.
• Moisture: Moisture buildup, from condensation when an engine cannot fully reach operating temperature, leaves additives unable to protect the engine from excess wear or prevent corrosion, carbon or sludge from forming.

Automatic transmission fluid (ATF)

Light red to pinkish, contaminated ATF becomes deep red to deep brown and loses its ability to properly lubricate internal parts and disburse heat. That allows sludge and varnish buildup, resulting in slipping or harsh shifting and other failures.

Here’s what these test stripes analyze:

• Moisture: High moisture levels can cause corrosion, fluid foaming, increased metal-to-metal contact and friction wear.
• Coolant: ATF that is foamy, milky pinkish color that indicates a failed radiator transmission cooler. Time to take it to the pros.

Power steering fluid (PSF)

Amber, light brown or reddish clear, PSF additives decompose from heat, friction and pressure, turning deep brown. It’s time to flush the power steering system when the fluid turns black from degrading rubber hoses, or milky tan from moisture.

Here’s what these test stripes analyze:

• Moisture and oxidation: Older PSF contaminated with air and moisture loses its lubricating properties and can foam, causing the steering to bind or lose power assist when turning.

Battery fluid

If your car has a non-maintenance-free battery (identified by the removable filler caps on the top of the battery), you’ll need to regularly check and top off the battery fluid.

A mixture of sulfuric acid and distilled water (aka electrolyte), battery fluid creates the electricity that makes modern batteries work efficiently. Schornstein suggests testing your tap water for pH, and hardness if you’re not using distilled water to top off your battery.

• Electrolyte: Using a hydrometer or refractometer, the specific gravity reading should be between 1.265 to 1.299, indicating a full state of charge. That means your battery is in good condition.

Pro tip: Always wear gloves and eye protection when working around a car battery or jump-starting a car. If you come into contact with battery fluid, flush with plenty of water and seek immediate medical attention.