Early car repairs save cash That new noise? Don’t wait until the repair becomes a horror story.

A 2002 Chevrolet Blazer had developed a small coolant leak from its radiator. According to Joe Ranker, the Hohokus, N.J., mechanic who spotted the leak, a repair would have cost about $400. But the customer decided to put off the fix. Within a few weeks, the Blazer's engine overheated, blew a head gasket, and needed a replacement of the cylinder heads, which cost the owner roughly $2,000. That scenario underscores the importance of monitoring your car's health and taking care of small problems before they snowball into service disasters.

A car will usually signal that something isn't right long before it has a major failure. Following the recommended maintenance schedule in your vehicle owner's manual is usually enough to avert many large problems. Routine maintenance items such as oil changes and tire rotations are performed on time, and during the accompanying inspections a trained technician can spot signs of trouble: leaks you might not have noticed, tiny cracks on the accessory belt, worn brake pads, or indications that front-end joints and bearings are wearing out.

If the warning signs are ignored, any of those problems could lead to expensive repairs in the future or even leave you stranded on the side of the road.

We spoke with a number of automotive mechanics across the country who had similar stories of owners who ignored early signs of trouble only to find themselves digging deeper into their wallets later to pay for needlessly costly repairs.

Tales of repair woes

Engine replacement: $6,000

Reason for repair

Sludge buildup due to not having motor oil changed for at least 11,000 miles.

What it would have cost

About $30.

What happened

Bruce Archuleta, a mechanic in Phoenix, had to replace the engine on a 2003 Jeep Liberty because a buildup of oil sludge blocked lubrication passages, causing the engine to fail.

How to prevent it

Change the oil according to the maintenance schedule (about every 7,500 miles for normal driving conditions or 3,000 miles for severe conditions). Failing to do so can cause excessive engine wear and create sludge in some engines, which forms when oil breaks down.

Engine replacement: $3,500

Reason for repair

Timing belt was not changed on schedule.

What it would have cost

About $600.

What happened

Mike Mikulski, a Haddam, Conn., mechanic, had to replace the engine on a 2000 Subaru Outback after its timing belt broke after 150,000 miles, allowing the pistons to collide with the valves. A used engine with a new timing belt was installed, keeping the cost from being much higher.

How to prevent it

The timing belt should be replaced as prescribed by the manual, usually around 60,000 to 100,000 miles. Many cars use a chain, which never needs changing.

Brake replacement: $400

Reason for repair

Owner ignored brake noise from worn pads.

What it would have cost

$100 to $200.

What happened

John Ibbotson, our own senior mechanic, had to replace the rear brakes on a friend's 2007 Hyundai Santa Fe because the pads had worn down to bare metal and damaged the discs. Had the job been done earlier, it might have been limited to replacing the pads and perhaps smoothing the discs on a lathe.

How to prevent it

On many cars, when a pad wears thin, a metal tang rubs against the disc and makes a squeal, warning that it needs to be replaced. Other signals include steering-wheel shake or noises when braking. A pad inspection at each tire rotation (about every 6,000 to 7,000 miles) should also be performed.

Engine replacement: $6,000

Reason for repair

Oil level was too low because of a leak.

What it would have cost

$100 to $1,000.

What happened

Steve Ouellette, a Higganum, Conn., mechanic, told us of a 2004 Acura TL that had to have its engine replaced because a lack of oil kept it from getting enough lubrication. A used engine kept the cost from being much higher.

How to prevent it

Check the oil level once a month, or every week if the car has a leak. Take your car in for service if the check-engine light is accompanied by another warning light or a change in performance. A leak caught early can be an inexpensive fix.

Transmission rebuild: $3,000

Reason for repair

Fluid was too low because of a leak.

What it would have cost

About $300 to $500.

What happened

Lance Wiggins, technical director for the Automatic Transmission Rebuilders Association in Oxnard, Calif., told us of an owner whose Mazda Protegé had a leaking axle seal. But instead of having his shop repair it, he decided to keep topping off the fluid. He overfilled the transmission, which made the leak worse. Eventually, the transmission's internal clutches burned out.

How to prevent it

If the transmission fluid is too low, it's probably because of a leak, which should be fixed. If you add fluid, don't overfill the transmission; that can make things worse.

New catalytic converter: $900

Reason for repair

Engine was not tuned.

What it would have cost

$300.

What happened

Auto-repair shop technician Frankie Jaquez in Middletown, Conn., replaced the catalytic converter on a 1999 Honda Accord—twice. The customer declined a $300 tuneup when it was first replaced and was back after 20,000 miles. The new catalytic converter became overtaxed because a dirty sensor caused the untuned engine to run too rich and it poured unburned fuel into the exhaust system.

How to prevent it

Regular tuneups are vital for optimizing the life of drivetrain elements and producing low emissions. The catalytic converter should have lasted 100,000 miles.

Windshield replacement: $430

Reason for repair

Windshield crack.

What it would have cost

About $60.

What happened

Bob Simpson, district manager for an auto- glass shop in Belleville, Ill., replaced the windshield on a 2005 Ford F-150 because a small chip grew into a long crack over time.

How to prevent it

Chips can be fixed for around $60, but in some states it's illegal to repair one in areas swept by the wipers.

New tires: $250 to $400

Reason for repair

Tires were not rotated.

What it would have cost

About $20 per rotation, or $100 over 30,000 miles.

What happened

Clint Dalton, manager of a Leesburg, Va., tire and repair shop, replaced a Nissan Sentra's tires after less than 30,000 miles because they had never been rotated. Those tires, with a 65,000-mile warranty, should have lasted much longer.

How to prevent it

Rotation is generally recommended every 6,000 miles by manufacturers. Also, check the tire pressure at least once per month; underinflation can cut a tire's life by as much as half. If your car pulls to one side, its wheel alignment is probably off, which also hastens tire wear. An alignment runs $50 to $100.