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10 Things You Should Never Do to Your Car

If your goal is to keep your car in great shape, don’t even consider doing any of these things or you’ll regret it.

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Dmitry Kalinovsky/Shutterstock

Take care of your car

Most people bring their car into the mechanic to get it fixed or looked at, but if you try to fix or check on things yourself there are certain things you should never be doing. Your car is probably one of the most expensive things that you own, don’t shorten its life by making one of these mistakes. Also, make sure to avoid these things you’re doing to your car that mechanics wouldn’t.

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never overfill tires
Family Handyman

Never overfill the tires to “get better gas mileage”

The Internet is brimming with testimonials from people who claim they upped their mileage simply by inflating their tires to the maximum pressure listed on the sidewall. What they don’t tell you about is the rougher ride, premature tire wear, longer stopping distances and increased repair costs due to worn-out suspension components.

The recommended tire pressure for your car is listed on a placard inside the driver’s door frame and it’s based on vehicle weight along with the best possible handling. Inflating your tires to the maximum pressure listed on the tire is okay if you’re hauling a very heavy load. But you must reduce the tire pressure to the recommended pressure once you remove the load. Driving a normal load on over-inflated tires reduces rolling resistance and that can increase your mileage slightly. That means you have less rubber in contact with the road, which reduces traction. Over-inflation increases stopping distances, causes the tires to slip and hydroplane on wet roads and reduces the life of the tire. The much harder tires also absorb less impact vibration so they transmit more road shock to your entire suspension system, causing a rougher ride. Worse yet, the additional tire bounce wears out your car’s struts, strut mounts, shocks, springs, ball joints and control arms much faster. Any mileage gains you get from decreased rolling resistance are more than offset by decreased safety factors and increased suspension repair costs. Never make these driving mistakes that make other drivers angry.

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wrong coolant
Family Handyman

Never use the wrong coolant/antifreeze

Whether you do your own cooling system flushes or are just topping off your cooling system after a repair, using the right coolant is critical to the life of your car’s engine and all cooling system components. The recommended coolant for your car is listed in your owner’s manual. If you use the wrong coolant or mix two different types of coolant you can actually cause early water pump, radiator, heater pipes and heater core failure. That’s because corrosion inhibitors are designed to be compatible with the specific metals used in the engine and cooling system. Each inhibitor package also has to be compatible with the types of plastic and rubber used in seals, gaskets, and tubes used in your particular engine. If you mix coolants, the corrosion inhibitors in one type of coolant can be incompatible with the additive package of the coolant already in your car. The inhibitors in the added coolant can reduce the effectiveness or even cancel out the performance of the corrosion inhibitors of the old coolant. Worse yet, topping off or flushing with the wrong coolant can damage the plastic and rubber seals and gaskets used in late model engines. The damage may not show until you’ve racked up 5,000 or more miles. But when those parts fail, you probably won’t connect the dots and realize they failed because you used the wrong coolant.

If you can’t find the exact coolant for your engine at an auto parts store, buy it at the dealer. You may spend a whopping $10 more than you would for the “universal” coolant stocked at the auto parts store, but at least you’ll get the right coolant for your car. That’s a small price to pay for peace of mind.

Changing coolant prevents premature radiator and heater core failure. That said, make sure you know these ways you’re wasting money on your car.

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brake fluid
Family Handyman

Never mix up brake fluid and power steering fluid

A one-pint bottle of power steering fluid looks almost like a 1-pint bottle of brake fluid. That’s why so many DIYers mix them up (it happens more often than you think). If you add the wrong fluid to either your power steering or brake system, the repair can easily cost upwards of $1,000. Power steering fluid swells the seals in a brake system, causing total brake failure. To fix the mistake, the shop has to rebuild or replace the master cylinder, calipers, wheel cylinders, and proportioning valve. Sometimes they even have to replace expensive ABS components. Pouring brake fluid into your power steering reservoir is just as damaging because brake fluid isn’t a lubricant, so it causes pump and steering gear failure. Always double check before you refill your brake or power steering fluid reservoirs. Watch out for these ways you’re shortening the life of your car.

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The tank of power steering in the car
Georgiy Myakishev/Shutterstock

Never use a “universal” fluid in your power steering or transmission

Several fluid manufacturers claim their “universal” power steering and transmission fluids work in all car makes and models. The car makers disagree and their arguments against using universal fluids are based on incompatible specifications, not greed. For example, there’s simply no way a single transmission or power steering fluid can meet the many different (and mutually exclusive) viscosity and additive requirements for every transmission and power steering system in use today. In fact, European, Japanese and domestic car makers have differing transmission and power steering fluid requirements from model to model and even year to year. The recommended fluid for your car’s transmission and power steering system is listed in your owner’s manual. If the auto parts store doesn’t stock the exact fluid, try a different store or buy it at the dealer. It’s simply not worth the risk to use a non-approved fluid in expensive components like your transmission or power steering.

For some nostalgia, check out these staff picks of unforgettable car stories.

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never disconnect
Family Handyman

Never disconnect a battery cable to test the alternator

Many years ago, you could disconnect a battery cable while the engine was running to test the alternator in your car. If the engine continued to run, that proved the alternator was working. But it’s a test you should never try on a modern car or truck equipped with computers and electronics. That’s because disconnecting a battery cable while the engine is running causes the alternator to spike a 25-125-volt surge within 40ms after cable removal. That voltage spike can’t damage anything in an old non-computerized car, but it can instantly fry the many computers and expensive electronics used on all late model cars. Repairing the damage can cost a small fortune. If your car or truck was built after the early 1970s, chances are it has at least one computer. So forget this old trick left over from the “old days” and test your car alternator with a volt meter. Or, take your car to an auto parts store that offers a free charging system diagnostic test. Then find out the secrets car dealers won’t tell you.

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Never drive when your oil light is lit

All cars have a “low oil pressure” warning light. If the light comes on while you’re driving, it can mean that your car is dangerously low or completely out of oil. Or it can mean that your car has a serious leak that’s causing a pressure drop, a clogged oil passage that’s causing oil starvation, or the oil pump has failed or is failing. Whatever the cause, when the light comes on, pull off the road immediately and shut off the engine. Then pop the hood and check the oil level using the dipstick. If the dipstick shows you’re out of oil or dangerously low, you must add more oil before restarting. Driving a car when it’s dangerously low or completely out of oil will destroy your engine in just a few minutes, and that can easily cost you $4,000. Don’t think you can drive to the nearest store to get more! It’s not worth the risk. Instead, call a friend or family member and ask them to bring the oil to your location (the recommended type and viscosity is listed in your owner’s manual). Add it to the filler port and check the dipstick to make sure it’s full. Do not overfill.

However, if the dipstick shows you’ve got oil, then the problem is even more serious and must be checked out by a mechanic. There’s really nothing you can do while you’re on the side of the road. If the dipstick shows the engine is full, or you can’t reach a friend to drop off more oil, call a tow truck! If you can’t afford a $200 tow, then you surely can’t afford a new engine.

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fuel gage

Never drive with less than a quarter tank of gas

The electric fuel pump is located inside the fuel tank on just about every fuel-injected car and truck. Car makers put it there on purpose so it’s cooled and kept at a safe operating temperature by the gas in the tank. But if you consistently drive with less than a quarter tank, the low fuel level can’t always provide enough cooling for the pump, and that can cause early fuel pump failure. In-tank fuel pump replacement can cost around $700. Overheating isn’t the only issue, though. Consistently driving with a low fuel level causes the pump to suck in debris from the bottom of the tank. That debris can pass through the “sock” filter in the tank and the particles can wear out the pump impeller, causing a low fuel pressure situation. This warning doesn’t mean you have to rush to a gas station the instant you hit a quarter tank on the gauge. The fuel pump can easily handle occasional low fuel level operation. But, if you consistently drive with less than a quarter tank, you increase your chances of early fuel pump failure and a big repair bill. Find out how much gas you should keep in your tank.

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Never use the wrong oil

Car makers have had to up their game on engine design to meet higher mileage standards. The newer engines are built to more exacting tolerances and include high-tech mechanisms like variable valve timing (VVT) and turbochargers to squeeze more power and miles out of every gallon of gas. VVT systems work by pulsing pressurized oil into hydraulic passages to advance or slow the camshaft. The pulse timing and associated camshaft movement is based on the oil type and viscosity listed in your owner’s manual. The computer varies the pulse rate based on engine temperature and driver inputs from the accelerator pedal. It all works great if you use the right oil and it gets messed up if you use the wrong oil. In fact, using the wrong viscosity oil can actually set a trouble code and light the “check engine” light on your dash.

The right oil is just as critical for proper turbocharger operation. A modern turbocharger can spin at rates as high as 240,000 RPM which means the bearings must be constantly lubricated and cooled by the oil. If you substitute a different oil type or viscosity, you can change the flow rate, causing bearing overheating and early turbo failure. Turbo replacement can cost $1,500 to $2,000.

So ignore the advice from your buddies or online “oil experts” and stick with the car maker’s oil recommendation. They designed the engine and they’re in the best position to know what fluids it needs. Then, read up on these 30 other secrets your car mechanic won’t tell you.

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clean car
Family Handyman

Never use dishwashing detergent to wash your car

Dishwashing detergent is designed to aggressively attack and break down dried on food, oil, and grease. That’s great for dishes—not so great for car paint. Car paint, clear coat and car wax contain oils and resins that maintain the paint’s integrity and filter out harmful UV rays. When you wash your car with dishwashing detergent, you actually strip off the wax and pull some of those critical oils out of the paint and paint sealants, leaving it bare and exposed to the elements. If you immediately wax your car with a high-quality wax, you can restore some of the UV protection. If you don’t wax your car after washing with dishwashing detergent, you lose important sun protection. If you regularly wash your car with dishwashing detergent, you’ll degrade the paint and clear coat enough over its life to cause premature fading and even early paint failure.

Car wash soap, on the other hand, is designed to remove dirt and grease without removing the surface wax and oils from the paint. It’s also biodegradable, so the wash water runoff is safer for the environment. Find car wash soap at any auto parts store or in the automotive aisle at most big box stores. It’s cheap and it’s better for your car’s finish. Make sure you know these 17 things you should always keep in your car.

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dip stick

Never neglect the dipstick

The oil change intervals listed in your owner’s manual are based on the car maker’s assumption that you’ll not only use the recommended oil, but that you’ll also check the oil on a regular basis and top it off when it’s low. All engines use some oil between oil changes; even some new engines can burn as much as a quart every 1,500 to 3,000 miles. If you never check your dipstick, you’ll never know that you need to add more oil. Worse yet, if you don’t top off your oil, you stress the remaining oil, dramatically reducing its useful life. Here’s an example: Let’s assume the recommended oil change interval for your car is every 7,500 miles. If you burn one quart of oil in the first 3.000 miles and don’t replenish it, you deplete the anti-wear and anti-corrosion additives in the remaining oil by about 25 percent. If you burn no more oil (which is unlikely), your oil will be worn out when you reach 5,600 miles instead of the normal 7,500 miles. If you continue to drive on that depleted oil until you reach the 7,500 mile mark, your engine can experience premature wear and develop sludge deposits. With an engine swap costing around $4,000, it pays to check your oil regularly and refill when it’s low.

The Family Handyman
Originally Published on The Family Handyman