by Eric Peters EricPetersAutos.com
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Well-intended people often do bad things to their cars without realizing it, or understanding what the possible consequences could be. So, which is worse?
Under or over-inflating tires?
Excessive air pressure in your tires will result in a harsher ride as well as faster (and uneven) tread wear. Youll be paying more for tires more often. Handling and braking performance may be negatively affected, too.
On the other hand, under-inflated tires are more insidious because people often dont know or notice that their tires are low on air mainly as a result of benign neglect and because tires, air valves (and wheels, if theyre aluminum) commonly leak air. A tire usually has to be really low on air maybe even close to flat before its visually obvious. Meanwhile, youre 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. The classic case being the Ford Explorer/Firestone tire debacle of the late 90s. People were driving at high speeds, on hot days on under-inflated tires. Which failed catastrophically and suddenly leading to numerous wrecks and deaths.
Point being: Check the air pressure in your tires with a gauge not just by looking at them at least every two weeks. Be sure theyre all filled to the specified pressure neither too much nor too little.
An extra quart in the crankcase? Or down a quart?
Many people take their cars to a quick lube place for oil changes. These places typically use a gun to shoot new oil into the engine as opposed to pouring it in a quart at a time. Its not uncommon for the result of this to be too much or too little oil in the engine. Whats the difference?
Running a quart low is less potentially damaging than running a quart over. Reason? If theres more oil in the crankcase than the engine was designed to hold, that oil has to go somewhere. What happens is it gets turned into a foamy froth as the engines reciprocating parts churn it around. This foamy frothy oil is less able to lubricate vital parts -which can lead to a catastrophic engine failure. Or, the excess oil might get sucked into the combustion chambers, where it gets burned partially with the resultant oily residue ruining expensive 02 sensors and catalytic converters.
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, its expected the level in the crankcase will occasionally be less than full. The engineers who designed the engine 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 immediately after every oil change, if you have your oil changed by someone else and at least every couple of weeks thereafter.
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 (everything made after that time) is the warm-up protocol.