Not too long ago, I purchased a compact Nissan pickup to fix up and recondition, with a goal of making the little Nissan my own bass-thumping, color-laden "minitruck." Not soon after a little yellow light on the dash flashed at me ... I could almost see the dollars flying out of my wallet.

So I took it to a local mechanic, who shall remain nameless. He told me that he ignored the engine warning light on his Toyota minitruck for three years, or until the bulb behind the engine light finally fused and his Toyota came to no grief. So I took a chance. But his advice extracted a heavy price on my Nissan: Just six weeks later, I got a significant loss of power and that dreaded white smoke pluming from my exhaust and, finally, a blown head gasket.

Sometimes a seemingly innocuous car problem can lead to bigger problems -- even a write-off -- if ignored. We took a look at five common car ailments or driver mistakes to inform you of the problems that can develop if left untreated.

Engine Oil Level Ignored

Most people know someone this happened to, usually a young or inexperienced driver. My wife's brother, for example, did this many years ago on a spring break trip from the D.C.-area to Florida. With a new driver's license and next to little know-how about cars, he reached North Carolina before his car, a VW Scirocco, ran out of oil and died on him. Cue an expensive tow home and an even bigger repair bill. Thanks dad!

What now?

Running out of oil is, perhaps outside of wrecking it, the worst cruelty you can inflict on your car. Oil prevents engine components from grinding together and prevents heat buildup. Denied its lifeblood for just a few miles your engine will swiftly seize up. Even if you refill with oil after discovering your mistake and the car is starting or running with the new oil, it's usually only a matter of time before a full seize-up occurs.

Fix or write-off?

You either need a new engine or a new car. Either way it's expensive. If the car itself is worth a lot more than the engine, then buy a replacement engine. If the car is old and barely worth a new or rebuild engine, start looking for a new ride.

Filled Tank With Wrong Gas

Again, seemingly everyone has a friend that managed somehow to do this at some stage in their life. It can happen to anyone who is in a hurry or distracted at the pump. My friend, Rob, was 17 and filled his old-school BMW 318i from the diesel pump instead of regular gasoline. Unaware of his error, he drove away and came to a rather bumpy stop within 100 yards.

What now?

Trick here is whether you realize you have made a mistake and how quickly you respond. Neither a diesel or petrol engine will run on fuel designated for the other. If this happens to you, it's important to try to avoid starting your engine, as this will cause the wrong fuel to circulate in your system, likely damaging some components in the process. The best thing is to get your car towed to a mechanic without starting the engine, and then get the mechanic to drain your fuel tank.

Fix or write-off?

It's more of an expensive repair option. A total fuel system cleanup and component repair can run into the thousands, while a simple drain will be hundreds only (or the more mechanically minded can do this themselves). This will make you think twice before picking up the wrong gas nozzle though.

Ignored a Fuel Line Leak

Aging fuel lines often crack and start leaking fuel, says Kenneth Lavacot, CEO of online mechanics' help site www.2carpros.com. Symptoms of a cracked fuel line are when you discover a puddle of fuel on the ground or frequently smell gas in your car. Most cars have a metal line that runs the length of the car with rubber fuel lines connecting at either end, one at the fuel tank and the other to the engine. Fixing a leaking fuel line is a simple task for a repair facility and costs between $60 and $120. Lavacot says it can easily be done at home by the semi-advanced mechanic.

What now?

Any driver who ignores a leaky fuel line is obviously at serious risk of becoming a fire casualty, Lavacot says, as gas is spurting from their car somewhere.

Fix or write-off?

Fix that leak. Not doing so may seriously endanger your and your car's lifespan. A fire in any part of your car will result, most probably, in a write-off, at least in any insurer's eyes.

Ignored a Water Pump Leak

"If your car's water pump is leaking engine coolant and you have left it unattended, it will cause your engine to overheat," Lavacot said. "Once this has happened, the engine's head gasket can rupture requiring major engine work to be performed."

What now?

Fixing a water pump is no big thing, Lavacot said, but a head gasket replacement is not easy and requires a qualified technician to perform this repair. Once the cylinder head has been removed, a machine shop will be needed to inspect the cylinder head for cracks using a pressure test procedure. If the cylinder head checks "OK" they will resurface the head to ensure a proper seal to the new head gasket. The technician will then reinstall the cylinder head and reassemble the remaining accessories. After the reassembly is complete the engine will be refilled with coolant and necessary adjustments performed.

Fix or write-off?

A cylinder head gasket replacement cost can vary greatly depending on the car's manufacturer. Be sure to receive a complete written estimate before work begins. A typical head gasket replacement will cost between $800 and $1,700 and go as high as $2,500 if the cylinder head(s) is/are cracked. Due to the major costs involved, consider the value of the car before the repair is started.

Failed to Change Timing Belts

Timing belts, among other things, regulate when your engine's valves open and close. If the timing belt or chain is broken or offset in any way, it can result in the valves not opening or closing correctly, which affects air intake, or, more seriously, the valves themselves can clatter into the engine block.Often, these need to be changed around the 70,000-mile mark (your car's owner manual will specify the time period or you can ask your service technician).

What now?

Aside from keeping your car off the road, damage caused by a flawed or un-replaced timing belt can lead to protracted insurance claim processes, with much forensic work conducted over engine-change receipts or just what -- usually lax maintenance -- caused the belt to seize.

Fix or write-off?

Replacing a timing belt is no biggie, but if your flawed or offset belt has resulted in bent valves and broken pistons, you're in real trouble here. Think new engine or new car.

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