How To Check the Fluids

To check the various fluid levels on your car, you seldom need anything more than your eyes, and a clean rag, or some paper towel (to wipe the dipstick before taking a measurement). There are tools involved in changing fluids, but cars and trucks are designed so that you can monitor the important fluid levels without having to get the toolbox out. You will need tools to check most modern automatic transmissions, but that is because they rarely leak these days and only need to be changed every 50-100k miles in most cases.

The fluids that should be checked on a regular basis include:

  • Engine oil
  • Coolant/anti-freeze
  • Power steering fluid
  • Brake Fluid
  • Windshield washer fluid
  • Diesel exhaust fluid

More and more vehicles are moving to electrically assisted power steering, so check your manual to see which fluids your car or truck has that need checking, and how frequently. Obviously, only diesel powered vehicles will have blue diesel exhaust fluid that need to be monitored and refilled.

How Long Should the Fluids Last?

With the advent of modern oils and additives, your vehicle's vital fluids last longer than they ever have – but that doesn't mean you should ignore the service intervals.

Engine oil: It's generally recommended that you change your oil at least annually if you don't put a lot of miles on your vehicle, or every 5,000 miles if you drive it every day. Most modern cars have a computer that takes into account things like ambient temperature, engine temperature, load, RPM, engine hours, and calendar days to remind you to change your oil when it needs it. Modern oils, filtration, engine design, and engine management systems have mostly relegated the 3 month/3,000 mile oil change interval to the history books for anything made in the 21st-century.

Coolant/anti-freeze: Coolant generally has a much longer service life with some manufacturers going so far as to call it "lifetime", but remember that always means the life of the warranty, not the real life of the car or truck. It is generally a good idea to flush and fill your cooling system at or before the 100,000 mile mark. The most important thing when topping off coolant, or refilling it, is to be sure to use the correct color for your vehicle; mixing incompatible coolant can cause internal corrosion, clogged cooling passages, or insufficient cooling.

Power steering fluid: Power steering fluid is a simple hydraulic oil that can last 100,000 miles or more if it isn't overheated. After 10 years, or when the odometer hits the 100,000 mark it is a good idea to drain and refill it.

Brake fluid: Brake fluid (and hydraulic clutch fluid, which is the same) can absorb water over time, so to prevent internal corrosion it should be replaced every 2 to 3 years. Since brake pads and shoes often have to be replaced every few years anyway, a good practice is to bleed the brakes at that time and refill the system with fresh fluid.

Transmission fluid/transfer case fluid/differential fluid: We have not mentioned manual transmission fluid, transfer case oil, differential oil, and only briefly touched on automatic transmission fluid here. These fluids vary greatly between different cars and trucks, but seldom need to be changed very frequently. Generally, 5 years or 60,000 miles between changes is enough, though if you tow a trailer, or operate in hot or dusty conditions, cutting that interval in half is a good idea. The exception to this is if you drive through water deep enough to get inside of these unsealed mechanisms, which requires changing the oil in them as soon as possible afterwards.

Obviously, windshield washer fluid and diesel exhaust fluid both should be replaced before they run out; they don't go bad from sitting.

How To Extend the Life of Your Car's Fluids

Operating your vehicle in a moderate manner is the best way to extend the life of all of its components. Avoid severe heat or cold, dusty conditions, towing, long up or downhill drives, and deep water. Don't rev the engine immediately on start up, or for the first few minutes before the oil can circulate or get warm. Treat your vehicle like the complex piece of machinery it is and it should last well beyond the length of the warranty.

In simple terms you should never exceed the recommended service intervals, either those from the vehicle manufacturer or the maker of the fluids. Over time oil becomes less slippery and reduces power, fuel economy, and performance, while increasing wear. Older coolant may still cool your engine, but it loses critical additives that prevent internal corrosion and lubricate parts like the water pump.

Not adhering to service intervals can decrease the reliability and life expectancy of your engine, so it's simply unwise to seek out a way to extend the life of your fluids. 

Why Do Fluids Need To Be Checked Periodically?

Obviously, the gas in your cars tank burns to make the engine run and needs to be replaced frequently or you can't drive anywhere. Much longer lasting, but only slightly less important are the rest of the fluids in your car.

A well cared for engine ought not to need more than a quart or two of oil between oil changes, unless there is a leak somewhere. But as the valve stem seals/guides and piston rings wear and age, more oil will get into the combustion chambers and be burned with the gasoline. Wear can also lead to blow-by, with oil vapors being pushed into the breather system and air cleaner by combustion gasses. Depending on the age of the vehicle and amount of miles on it, you may want to be checking the oil level once a week, and certainly once a month, even for late model vehicles.

Your car's cooling system is sealed, and only vents to the atmosphere in the even of the car overheating. You should make it a point to check the level of coolant in the overflow tank whenever you happen to be under the hood, just to be safe. If the cooling system develops a leak, you may not notice it until you lose enough fluid to make the car overheat, and overheating can cause serious engine damage. Your car can lose coolant in a number of ways that are not as dramatic as steam pouring out of the hood.

Power steering and brake fluid are important for for the safe operation of your car. If a power steering hose were to leak you might not notice until it becomes much hard to steer the car because of a loss of fluid. The brake fluid level will sink as the pads wear and the fluid has to push the pistons further out for effective braking. In extreme cases, or if there is a leak somewhere, the fluid level can sink so low that the brakes become spongy due to air bubbles in the system. 

You never can tell when you are suddenly want to use your windshield washers - maybe there is a sudden glare of sun across a dirty window, or maybe you just got splashed with mud making it hard to see. Better to keep the washer reservoir full so that in an emergency you have a way of cleaning your windshield without stopping.

Unlike the rest of the fluids mentioned, DEF does get used periodically without you even noticing it just by running your diesel engine. Most vehicles will warn you when you are getting low so you can fill up at your next fuel stop. If you are on a long trip, through the sort of country where billboards advertise "last fuel for 100 miles" you should check the DEF level when filling up to avoid running out in the middle of nowhere.


How Much Does Topping Off Your Fluids Cost?

The more important question is, how much does it cost if you run low on some vital fluid? Checking and filling up all of the fluids on your car will likely cost you less than $25, and that's if you have to add a little bit of EVERYTHING.

Typically, you'll find you may be a quart low on oil, which will cost you $5 or so. Running low on oil causes increased wear and tear, but you may not notice any difference except under extreme conditions; hard cornering or high G braking may starve the engine of oil for a few seconds.

Being low on antifreeze/coolant, or windshield washer fluid will likely cost you that, or less, for a whole gallon. And remember, both can and should be diluted 50/50 with clean tap water.

Brake fluid is also about $5 for a pint bottle, and you should always use fresh fluid, less than a year old and store in a dry place in a sealed container. Power steering fluid is even less expensive, though your car may take a special formulation that is slightly more. Check your manual.

Diesel exhaust fluid, typically sold under names like "Blue DEF" and "Ad Blue", costs $10-20 for a 2.5 gallon jug, which ought to last you many tanks of fuel, and thousands of miles.