Monthly Archives: June 2017

Specs for maximum performance and efficiency

Actually, there is no such thing as a tuneup in the traditional sense of replacing parts to bring the ignition and fuel systems up to specs for maximum performance and efficiency, and there hasn’t been for years.

About the only things left from the traditional tuneup are new spark plugs, which is typically done every 100,000 miles, and replacing the air filter periodically. The federal EPA and Department of Energy say that replacing a clogged air filter will not improve gas mileage but can improve acceleration 6 to 11 percent. The agencies do not say what benefit can be derived from fresh spark plugs, but computers that control today’s engines adjust the air-fuel mixture and spark timing to compensate for wear, such as when the electrodes on spark plugs are worn down.

Even so, some car owners still dutifully take their car in periodically to have it “tuned up.” Instead, service technicians will inspect and perhaps test the fuel, ignition and emissions systems to look for faulty vacuum hoses,oxygen sensors and other parts that can hurt performance. The federal government, for example, says a bad oxygen sensor can give engine computers false readings and reduce fuel economy as much as 40 percent.

Having your vehicle serviced and inspected periodically is a good way to extend its life and keep it operating efficiently. However, walking into a repair facility and asking for a tuneup is a bad idea because it indicates you’re still living in the previous century and have extra money you would like to spend. Some in the auto-repair business will take advantage of those opportunities.

Are You Need a Valve Clearance Adjustment

It could, depending on the age, condition and brand of vehicle you’re driving. The maintenance schedules for some recent Hyundai engines, for example, call for a valve clearance inspection at 60,000 miles. Some Hondas call for an inspection at 110,000 miles. Some manufacturers advise valves should be inspected only if there is excessive valve noise. Others don’t mention valve clearance in their maintenance schedules.

Valves are opened by camshaft lobes on overhead camshaft engines and by rocker arms on pushrod engines. With extended time and use, the original clearances between these parts and the valve stems become bigger (with exhaust valves, the clearance can become tighter over time). That often leads to a clattering noise or more engine vibration that a driver might not notice for quite a while, because it increases gradually.

Intake valves open and close to let the air-fuel mixture (or just air in some modern engines) enter the combustion chambers, and the exhaust valves allow exhaust gases to escape. Too much or too little valve clearance can result in poor performance or a rough idle because the engine can’t “breathe” normally and operate at peak efficiency. Too much clearance means the valves will likely clatter and, over the long term, cause damage to the valves and/or camshaft lobes or rocker arms. If there’s too little clearance the valves won’t fully close, causing excessive heat, and the engine will lose power.

If your engine generates a loud clatter, it could be time for a valve clearance adjustment — though on some engines the valves don’t generate noise when there’s too much clearance. Loss of power could be a sign of a weak or broken valve spring, and a tapping noise could be caused by a loose rocker arm, so a clearance adjustment may not be all that’s needed. The mechanic won’t know for sure without inspecting the valves.

Because adjusting valve clearance (or “lash”) requires removing the valve cover (or covers on V-type engines) and checking both intake and exhaust valves, it isn’t a quick in-and-out maintenance item like an oil change, especially on engines that have three or four valves per cylinder. Plan on at least a few hours at the shop and a charge just for the inspection.

The Crankshaft Position Sensor

Most owners probably don’t know that their vehicle has a crankshaft position sensor until the engine dies, won’t start or starts running poorly. Then they find out they need a new one.

The crankshaft position sensor, typically mounted near or on the crankshaft, tells the engine computer how fast the engine is running. That’s so the control unit knows when the spark plugs should ignite the air-fuel mixture and, in some engines, when to inject fuel. These sensors are used on virtually all engines that have distributorless ignition systems.

If the sensor fails, the computer won’t know how to set the ignition timing, so the engine may stop running or refuse to start. It could also stall or run badly, possibly triggering the check engine light. Excessive heat is a frequent reason these sensors fail, and they also can stop working because of faulty electrical connections or wiring.

Some vehicles also have a camshaft position sensor that allows the engine computer to monitor the position of the camshafts (or camshaft), which open and close the valves, for more precise fuel and ignition management.

These sensors are not listed as routine maintenance items, but they often fail without warning. For that reason, some repair shops recommend they be replaced on high-mileage engines as preventive medicine.

The manufacturers recommendations

Maybe forever, if you rely on an overly liberal interpretation of the maintenance schedules set by some vehicle manufacturers. That doesn’t mean you should ignore them or even accept the manufacturer’s recommendations, though; instead, add them to your list of items that should be checked annually after the first three or so years of ownership.

With accessory drive belts, most manufacturers recommend only a periodic inspection for cracks, fraying or other visible wear, and on some GM vehicles the first inspection isn’t until 10 years or 150,000 miles, when someone else might own the vehicle.

Hoses? What about them? Most owner’s manuals don’t even mention radiator or coolant hoses (except that they can get really hot on an overheated engine). Other hoses, such as for the power steering or air conditioner, usually are mentioned only as something that should be checked as part of routine maintenance or when leaks are suspected.

Coolant hoses typically last several years, though anything longer than 10 years may be pushing the limits. Rubber weakens with age and from repeated exposure to hot coolant, so the older they get the higher chance they’ll leak and cause the engine to overheat.

Drive belts are usually the serpentine type that snake their way around pulleys to power the alternator, air conditioning compressor, power steering pump and perhaps the water pump, and they’re designed to last several years.

When to replace a drive belt is a judgment call by a repair technician, and it’s up to the vehicle owner to decide if the time is right given the manufacturers have largely chosen to stay out of it. We would err on the side of caution, because when a drive belt breaks your car comes to a halt. Depending on where this happens and when, a belt that fits your car may not be available until tomorrow, leaving you stranded.