• Oct 24, 2010
When you should change your vehicle's fluids depends on... When you should change your vehicle's fluids depends on the kind of driving you do. (exfordy, Flickr)

Have you ever tried to actually read your owner's manual, especially the part about maintenance and service? As if this kind of stuff isn't confusing enough, there are always two schedules listed, one for a vehicle driven under "normal" conditions and another for "severe." But what exactly does this mean? I have yet to see an automaker that actually explains, in plain English, what these terms mean.

This article is the second in a series of four that addresses the differences between severe and normal service recommendations. We've already covered engine oil, so now we're moving on to the rest of the fluids in your vehicle: transmission fluid, differential and transfer case lubricants, engine coolant, power steering fluid and brake fluid.

Service Schedules For Fluids

Let's start by trying to understand the differences between normal and severe. The severe schedule, which always has shorter recommended intervals between fluid changes, applies if any of the following are true:

  • Most trips are less than 10 miles (16 km). This is particularly important when outside temperatures are below freezing.
  • Most trips include extensive idling (such as frequent driving in stop-and-go traffic).
  • The vehicle is frequently driven in dusty areas, like on dirt or gravel roads.
  • The vehicle is frequently used for towing a trailer or using a carrier on top, both of which place extra demands on the engine.
  • The vehicle is used for delivery service, police, taxi, or other commercial applications

If none of these conditions are applicable, you should go ahead and follow the normal schedule. Your owner's manual will tell you the specific mileage suggestions for your vehicle, thus, make sure you check it for the recommended fluid, lubricant and filter change intervals. Keep in mind that with these fluids, there's not exactly a rule of thumb like there is with engine oil. In fact, some of the items discussed in this article may not be listed in your service schedule. If this is the case, consider our recommendations suggested under each section.

Transmission Fluid

While some manufacturers suggest that transmission fluid can last for up to 100,000 miles if you're following the normal schedule, I tend to think that this is one of the cases where it's better to be cautious and follow the severe schedule if there's any question. A severe service schedule might call for transmission fluid to be flushed at 35,000-40,000 miles, and at usually less than $200 for this procedure, it's good prevention. Getting an automatic transmission rebuilt is a costly repair, easily running into the thousands of dollars, so it's one you particularly want to avoid.

The transmission fluid performs a few functions. It serves as a medium by which the hydraulic pressure, necessary to operate the transmission, is created. It absorbs heat within the unit and carries it away to the transmission oil cooler, insuring that the transmission does not overheat. This vital fluid also lubricates the moving parts inside the transmission. Finally, it keeps dirt and debris in suspension until the filter can remove it from the fluid.

Transmission fluid is an oil, and is therefore subject to viscosity breakdown and the loss of its protective, lubricating, and cooling properties. Operating the transmission on fluid that is worn out results in premature transmission wear and ultimately failure.
In determining which service schedule to use for your transmission fluid, there are a few key real-world activities that indicate you should use the severe interval. These include towing, frequent driving in stop-and-go traffic or spending long periods of time with the vehicle idling, driving your vehicle off-road, hauling heavy loads, or using a snowplow. Following this more vigorous severe maintenance schedule will help head off the damage caused by excessive friction, heat, and internal wear, which can kill your transmission.

Differential And Transfer Case Lubricants

First a note: Most modern front-wheel-drive cars do not require this sort of service, because they don't have transfer cases or serviceable differentials. Servicing the transfer case and differential is usually applicable to four-wheel-drive, all-wheel-drive and rear-wheel-drive vehicles. While not all will require frequent service in this area, it can still be necessary, especially if you're a candidate for the severe service schedule. Most manufacturers do not require the transfer case or differential to be drained unless there's a problem, but the fluid should be regularly inspected.

Differentials turn the axles that turn the wheels, while the transfer case is an auxiliary gearbox that allows a four-wheel drive vehicle to shift from low to high range and back again. Each of these gearboxes house lubricant to keep them running smoothly and keep them cool.

The best way to determine whether your transfer case or differential needs its fluid changed is by a visual inspection of the fluid. Lubricant that contains metal flakes indicates internal wear. If this is the case, the unit should be opened up and inspected. Fluid that is black has been overheated and the unit should be inspected for the cause of the overheating, alas wear is the usual cause). Fluid that is milky in color has been contaminated with water and should be changed immediately to avert premature failure. Also check for open or broken vents that allowed the water in and repair them.

Years ago, 90-weight gear oil was the only lubricant used in differential or transfer cases. However, today's carmakers use specially formulated lubricants in many of these units. These special additives can be specific to your vehicle and can make other gear oils incompatible, so make sure you check your owner's manual for the exact fluid specifications.

Engine Coolant

Engine coolant runs through your vehicle's engine, absorbing and transferring heat to the radiator where it is cooled before being re-circulated. Coolant contains specially formulated chemical packages that inhibit rust and scale buildup, lubricate water pumps, help protect against freezing, and improve heat transfer.

There are plenty of things that can cause your coolant to "wear out": Not changing it frequently enough, running the engine in an overheated condition, and even just working the engine extremely hard can result in breakdown of the coolant's chemical properties. This leaves the cooling system more susceptible to rust and scale buildup and freezing in the winter. In addition, the water pump can wear out from excessive friction and heat.

The rule-of-thumb for flushing and replacing your coolant is every two years or 24,000 miles.

Power Steering Fluid

Power steering fluid is hydraulic oil, just like transmission fluid. Your power steering system consists of a pump and fluid reservoir, lines, and a power steering gear. The pump creates hydraulic pressure from pumping the fluid, which powers the steering gear, making steering easy.

On most vehicles, power steering fluid does not show up in the maintenance schedule, so there are no severe or normal service recommendations. The only recommendation suggested here is to check it at every oil change, inspecting closely for evidence of metal flakes, indicating steering gear or pump wear, or a black or dark color, indicating overheating. Either condition calls for replacement of the fluid and inspection of the system. If the fluid appears to be overheated, the pump should be checked for internal wear. If you catch these problems early enough and replace the pump, you can usually circumvent replacing the steering gear later.

Brake Fluid

On most vehicles, brake fluid does not show up in the maintenance schedule and so there are no severe or normal service recommendations. The only recommendation suggested here is to check the brake fluid every oil change, inspecting closely for the proper level and signs that the fluid needs to be changed. Some manufacturers do suggest having the brake fluid completely changed every five to seven years, especially if you live in a state where you experience winter or a lot of rain.

Brake fluid is a hydraulic fluid used as a medium to generate the pressure needed to activate the brakes. When you press the brake pedal, the master cylinder pumps fluid through the system, which pushes the brake caliper pistons against the brake pads, which in turn make contact with the brake rotors and slow the car.

Brake fluid that is black in color has been overheated. Excess heat in the system is usually caused by a stuck brake caliper. So if the brake fluid is dark in color, the brakes should be checked for a malfunction. Rust sediment is an indication that moisture has contaminated the brake fluid. You need to keep a close eye on brake fluid because it is hydroscopic in nature, meaning it absorbs moisture, which reduces the effectiveness of the fluid.



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    • 1 Second Ago
  • 109 Comments
      you knucklehead
      • 5 Days Ago
      Everyone's an expert. Here's a rule of thumb, if the guy recommending fluids and service intervals can't spell or form a sentence, go somewhere else. Jiffy, speedy, quick, rapid, Etc. Lube joints, hire the guys that can make it to work every day. That's their only true requirement. The guys that can make it into work each day are being trained by some other idiot that got his background in oil, working the fry-o-lator at some fast food joint. Find a specialist that you can trust, and stay with them. Develop a solid working relationship and stop worrying. Find a guy by word of mouth, flashy ads and empty promises don't make a good shop. If you are uncomfortable, move on. If you are happy with your Tech, do him the favor of spreading it around. We,re not all waiting in the shadows to bend you over the dresser. (But there are many of those guys out there.) Just pay attention, and ask around before you drop off one of your largest purchases.
      GrandDaddy
      • 5 Days Ago
      This has nothing to do with car maintenance but is a valid question for a motorcycle; especially Harley Davidson. A typical car requires the oil to be changed in the 1st 3000 miles and cost maybe around $35 on average. But for a Harley; the 1st service is advised at 500- 1000 miles and can cost as much as $250 then another service at 2500 and again at 5000 miles. Each time costing about the same. So the cost of maintaining a Harley is about $700-750 for the 1st 5000 miles. A car would be only $70 for the same mileage. Ten times the cost of a car.Is the recommended Harley maintenance really necessary ? Or is this just a away for the already overpriced Harley to make more money?
      dangenrosy
      • 5 Days Ago
      LOL...for Marksnothere.... he is ASE certified master mech. He uses mobil 1 every 3k miles, just like my friend, in is 2002 chev malibu. I asked him why he use expensive synthetic and change every 3k. He said because I love the car and it will last forever. So I said can I have your used oil for my next oil change and he said that his mechanic burns it in a heater during the winter to heat his garage. -----My Dad always said never love something that can't love you back.----- Three months later his wife totaled his Malibu!
      ccdae5
      • 5 Days Ago
      judithfrf - wow, thanks for the info, another good reason not to buy a Chrysler. Exactly what maintenance is required before 30k miles to maintain a Chrysler transmission warranty?? If any, it's obviously too much!
      ccdae5
      • 5 Days Ago
      Here's a trick for the cabin air filter. If they get a bit musty smelling in the summer. Turn the AC on "recirc" and the fan on medium, then spray some lysol air freshner under the dash on the passenger side. It will be drawn into the system and freshen the filter, you can stop when you smell the Lysol coming out of the dash vents. Note: cigarette smoke kills cabin air filters quickly. Good luck.
      • 5 Days Ago
      Oh me; oh my! Whatever are we to do? Do this; do that. Don't do this; don't do that. Just do what you and your trusted mechanic think are necessary and the car will either run like a top or it will spit up on you and then you will know you needed to do things more frequently - sigh. My mechanic is so fed up with people panicing about what needs to be done. He states we over react to the car's needs. And yes, I have used him for over 20 years and have recommended lots new customers to him. He has so much work, he does not NEED to perform unnecessary services on our vehicles....oh happy day!
      • 5 Days Ago
      I change my oil filter every 5k miles and only add oil because the filter takes about one qt. and the engine uses about .25 qt's per 1k miles. Thats a little over 2 of the 5 qt's in the engine. I tested my oil for a long time and found that the ph value did not change over a year. Flushing your trans. is a rip off. The trans needs to be changed every 30k miles or you will be buying a new one. It is very easy to change the trans. fluid. Don't believe the mechanics. I can change my trans fluid in 30 minutes including letting it drane for 20 minutes. Flushing does not get all the fluid out. I have seen mechanics raise the car, clean off the bottom of the trans, and make sure it is full and give it back to the customer and tell them they flushed it. Far too often. I was a auto mechanic.
      gr8bsn
      • 5 Days Ago
      Did you know that GM seals their automatic transmissions now? They've removed the dipstick so that the owner can not check the state or level of their own fluid anymore. To make matters worse, the only place that has the proper tools to check and service my transmission are a GM dealer. Supposedly, at 30K miles, I have take the service writer's (AKA commissioned sales person's) word for it and pay $300 for a flush that I know I don't even need. Come on people! I'm not that gullible! My old Ford Explorer that I use for a work truck has almost 200K on it and the transmission goes at least 50K between flushes and works just fine. Just wait until they take the oil dipstick off the engine. See, they do this slowly to get us used to it. Pretty soon, we'll have no control over our own vehicle maintenance anymore. They'll have some annoying bell that goes off, or engage "limp mode" until we take it to a dealer to pay $500 to have the oil checked. You don't think they'll do this, they're already halfway there! I get emails from my own damn car whenever the tire pressure gets too low!
      Ken
      • 5 Days Ago
      I'm old and suffer from COPD, and I will admit I do not have my autos serviced as often now. I once did this all myself, and actually enjoy the labor, but now I have to pay others to do it. I find that now I push the mileage a little on all requirements. Oil changes that once were performed at 3000 miles now get done at 5000. Others are done if a visual inspection or perform indicates their need.
      sir
      • 5 Days Ago
      I think you mean brake fluid is "hygroscopic"
      • 5 Days Ago
      I FIND THE COMMENTS QUITE INTERESTING, AND REALLY MUCH BETTER THEN THE ARTICLE...I OWNED A 94 CAMRY, AND "GAVE IT TO A FAMILY FRIEND" AT 200K, AND 10 YEARS OLD. THAT CAR WAS PROBLEM FREE AS FAR AS BODY & HEAVY MECHANICAL. KEPT THE SERVICE WORK UP TO DATE AT EVERY 7,500 MILES. I DROVE 50 MILES TO WORK EVERY DAY. IN THAT SAME PERIOD, I BOUGHT TWO GM SUV'S IN 1999. SAME MAINT SCHEDULE. SAME USAGE. I STILL HAVE THE GM SUV'S, AND WILL BE BUYING 2 NEW SUV'S THIS FALL. I WILL NEVER BE A GM OWNER AGAINI! HAVE OWNED GM PRODUCTS SINCE EARLY 1960'S, AND BEEN FAITHFUL TO THE LABLE EXCEPT FOR THE TOYOTA. KEPT THE SAME DEALER, TOO. IN THE PERIOD OF THE LAST 10 YEARS, MY SUV'S HAVE "ATE-UP" THE BRAKES IN THE FRONT. I SUED GM, WHEN I WAS FORCED TO PAY FOR A PROBLEM THEY KNEW EXISTED ALL ALONG.....FRONT RIGHT BRAKE PARTS FAILURE. (ANYONE DO PRESSURE TESTING ON ALL FOUR CORNERS TO SEE WHY THERE IS THIS FAILURE?) WELL I WATCHED A PAIR OF KIDS ON TV REPAIR A SUV WITH THE SAME PROBLEMS I USED TO HAVE ON BOTH SUV'S. WENT TO A MIDAS SHOP, NO MORE GM DEALER HERE, AND HAD BOTH VEHICLES INSPECTED, AND CHANGED OUT THE GM PARTS, AND LET HIM USE HIS "COMPANY PARTS". NOW HAVE A WARRANTY, AND MAYBE EVERY COUPLE OF YEARS I GO BACK FOR PADS. NO MORE $1200 COMPLETE BRAKE JOBS AT GM DEALER, 7 TIMES IN 40 K! THATS WHY I SUED!..(THEY HONORED THE REPAIRS UP TO 36K) I AM NOT A LEAD FOOT, OR HOT-RODDER... OH YES, THE MAJOR PROBLEM: GM SPEC'S FOR THE ???ROTORS??? HAVE INSUFFICIENT NICKLE IN THE METALIC COMPOSITION?? I AM IGNORANT TO THE ACTUAL PROBLEM, BUT AFTER WATCHING THOSE TWO FELLAS & A GARAGE ON TV, I AM NO LONGER FRUSTRATED WITH MY CHEVIES, JUST THE DEALER & MFG. MY NEXT SUV'S? FROM TOYOTA.......I REPLACED WINDOW ACTUATORS ONE TIME EACH SIDE AT AROUND 150K, AND ALL 3, YES, 3, O-2 SENSORS AT 90k. NEVER TUNED IT UP WITH A WRENCH, AND USED FI CLEANER WHEN MILEAGE DROPPED UNDER 30MPG. USED 100% SYNTHETIC IN MOTOR. SEEN NEWEST OWNER, AND THEY HAVE 370k+, AND STILL NO MECHANICAL PROBLEMS, AND TO THEIR KNOWLEDGE IT STILL HAS THE SAME SPARK PLUGS. I AM NOT A MECHANIC, I JUST READ WHAT YOU CONTRIBUTORS COMMENT ON, AND REFLECT BACK ON MY PROBLEMS FROM THE PAST........GOOD-BYE GM! ONLY 3 MORE MONTHS BEFORE I AM FREE OF THE LABEL.....YOU DID IT TO YOURSELF!
      • 5 Days Ago
      dugandob, i believe you meant to say "jollies"
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