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Thread: Bad - and worse - things we do to our cars

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    Vulture of The Western World Eric's Avatar
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    Bad - and worse - things we do to our cars

    What's worse?

    * Under or over-inflating tires?

    A couple extra psi of air pressure in your tires will result in a harsher ride as well as faster tread wear. Tires inflated significantly above the maximum recommended pressure may also pop just like a balloon, especially if the vehicle is overloaded (a truck, say) or driven at high speeds for an extended period of time.

    On the other hand, under-inflated tires are more insidious because people rarely over-inflate their tires while under-inflated tires are commonplace - mainly because tires, air valves (and wheels) commonly leak air. Also, the condition often goes unnoticed. A tire has to be really low - maybe even close to flat - before it's visually obvious. Meanwhile, you're driving around on a tire (or tires) 5, 10 or even 20 psi below the recommended pressure - which can lead to weird handling/poor braking, even a sudden failure due to the heat build-up (see: Ford-Firestone).

    * An extra quart in the crankcase? Or down a quart?

    Running a quart low is far less potentially damaging than running a quart over. Reason? Excess oil in the crankcase is more than the engine was designed to hold - and that oil has to go somewhere. What happens is it gets turned into a foamy froth as the engine's reciprocating parts churn it around. This foamy frothy oil is less able to lubricate vital parts - and can also end up where it shouldn't, which in a modern emissions controlled car can lead to other (expensive) problems.

    On the other hand, most engines will not be harmed if run a quart or so low for a little while. Since all internal combustion engines use a certain amount of oil during normal operation, it's expected the level in the crankcase will occasionally be less than "full." The engineers who designed the engine know this - and designed in an extra margin of total oil capacity for just this reason.

    The key thing is to be sure to check the oil level at least every couple of weeks. You don't want to run below the safe margin - typically about a quart less than "full" - which could result in catastrophic engine failure and a massive repair bill.

    * Drive off right away - or "warm it up" a little first?

    One of the biggest differences between "old" cars (those built before the widespread adoption of electronic fuel injection and computer controls in the mid-late 1980s) and "modern" cars is the warm-up protocol.

    Older cars without computers (and with carburetors) needed more cold-start hand-holding. It often took a couple of minutes for the choke to turn itself off and the engine to settle into a comfortable (and stall-free) idle. With modern cars, warm-up happens much faster. Most owner's manuals say it's fine to drive away normally within 30 seconds or so after start-up.

    Nonetheless, you'll do your (modern) car a favor by taking it easy for the first 10-15 minutes of driving. Wear and tear is still highest when the engine is cold - even if a modern car's cold start drivability is much better than an old car's. By avoiding full throttle starts and being gentle until the entire car - engine, transmission, brakes, etc. - have reached full normal operating temperature - you'll help the car last longer.

    Tip: If your vehicle has a manual transmission, let the clutch out (with the transmission in neutral) during that initial 30 seconds after start-up. This will circulate gear lube inside the transmission, coating all the critical parts. Reduced wear and tear - and easier shifting - will be your reward. (Automatic transmissions do this automatically, whenever the engine is running and no matter what gear the vehicle is in - so you don't need to do anything.)

    * Ride the brakes - or "gear down"?

    Descending a steep grade, which is smarter: Using the brakes to keep the car from picking up too much speed? Or downshifting to a lower gear and using engine braking to achieve the same thing?

    Replacement brake pads (and even calipers and rotors, etc.) are a lot cheaper, usually, than a new clutch or rebuilt transmission. So the argument from the economical perspective is: Use the brakes - and save the wear and tear on your clutch/transmission.

    On the other hand, how much is you life worth? Riding the brakes for extended periods on steep downhill grades may heat them up to the point that braking power starts to fade. If that happens, you won't be able to stop the car as quickly (maybe not at all) if an unexpected emergency situation comes up. Cars with high-performance brake pads/systems are more fade-resistant, but they're not immune from this problem, either.

    So, it's more sensible to put the transmission in a lower gear to keep the car from building up too much speed on extended downhills.

    If your car has an automatic, going from "OD" to "D" (or just turning off the overdrive by pushing the button, if applicable) is usually sufficient, but you can always go down one more to 3 or even 2 if need be. With a manual, downshift to the gear that maintains the speed you want without your needing to ride the brakes.
    Last edited by Eric; 03-23-2009 at 08:15 AM.

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    Quote Originally Posted by Eric View Post
    * Ride the brakes - or "gear down"?

    On the other hand, how much is you life worth? Riding the brakes for extended periods may heat them up to the point that braking power starts to fade. If that happens, you won't be able to stop the car as quickly (or maybe not at all) if an unexpected emergency situation comes up. Cars with high-performance brake pads/systems are more fade-resistant, but they're not immune from this problem, either.
    As you say, far better to use the gears; if you do need to use the brakes, don't ride them - brake fairly hard for a short distance,then take your foot off the pedal; that way, you'll keep your speed down without generating excessive heat.

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    Vulture of The Western World Eric's Avatar
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    Quote Originally Posted by Dave Brand View Post
    As you say, far better to use the gears; if you do need to use the brakes, don't ride them - brake fairly hard for a short distance,then take your foot off the pedal; that way, you'll keep your speed down without generating excessive heat.
    Yep!

    I happen to live near a very steep, extended downhill grade. I have experimented with various test cars to see how riding the brakes the entire way down affects braking performance. In a few cases, by the time I got to the bottom of the mountain, the front rotors were visibly glowing from the heat!

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