Engine Frequently Asked Questions
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2020 Corvette V8 engine

Engine Frequently Asked Questions

by Larry Carley copyright AA1Car.com

Q. What is the most important thing I can do to make my engine last as long as possible?

A. Regular oil & filter changes. Oil and filters are a lot cheaper than replacing an engine. Although many OEMS are recommending oil changes as high as 7,500 to 10,000 miles or more on many late model vehicles, our recommendation is to change it every 5,000 miles, especially if you do a lot of city stop-and-go driving or short trip cold weather driving.

Regardless of the type of oil you use, moisture builds up inside the crankcase, which over time can form acids and sludge. Changing the oil on a regular schedule will prevent oil breakdown and prolong the life of your engine.

Q. What are the 6 most common engine problems?

A. (1) Oil Leaks, (2) Oil Consumption, (3) Loss of Compression, (4) Broken Timing Belt, (5) Head Gasket Failure and (6) Loss of Oil Pressure.

Q. How Do You Stop an Engine Oil Leak?

A. Replace the leaky gasket or seal. Oil leaks are the result of old or damaged engine gaskets (oil pan, valve covers, timing cover and/or intake manifold gaskets), and/or worn or damaged crankshaft or camshaft seals. On some engines, RTV sealer is used to seal oil pan, timing cover and valve covers instead of gaskets. These too may develop leaks as the engine ages. The only cure for a leaky gasket or seal is to replace the old gasket or seal with a new one.

Q. How Much Oil Should An Engine Use Between Oil Changes?

A. Almost none. Although some vehicle manufacturers say it is "acceptable" (by their definition, not ours!) for certain engines to use as much as a quart of oil between oil changes. However, most late model low mileage engines that are in good condition should NOT burn more than half a quart of oil between changes. Most will actually use less than a pint of oil between changes.

As the miles add up, internal wear in the engine's cylinders, piston rings, valve guides and valve guide seals allow more and more oil to seep into the combustion chambers. If an engine is burning a lot of oil, you will likely see blue smoke in the exhaust when the engine is first started and when the vehicle accelerates.

There is no miracle oil additive that will stop oil burning. Some additives may slow it down a bit, but not enough to even justify the cost of the product. If the main cause of the oil burning is worn valve guide seals, replacing the seals may reduce oil consumption significantly or completely. But if the cause is worn or damaged piston rings or cylinders, the engine will have to be rebuilt or replaced to fix the problem.

See Causes of High Oil Consumption

Q. What are the most common causes of Loss of Compression in an Engine?

A. Loss of compression is often due to one of five conditions: (1) Worn or damaged piston rings that allow compression to blow past the pistons, (2) bent, worn or damaged valves that allow compression to leak past the valves ,(3) a broken valve spring that prevents a valve from fully closing, (4) a blown head gasket that allows compression to leak between adjacent cylinders or the cylinder head and block or (5) a broken timing belt or chain that prevents the camshaft(s) from turning, which in turn prevents all of the valves from opening and closing resulting in ZERO compression and a dead engine. These are all major problems that will require engine disassembly, replacing the worn or damaged parts, or rebuilding or replacing the engine itself to fix. Again, there are no miracle additives in a can that can restore lost compression due to any of these factors.

Q. What Happens If My Timing Belt Breaks?

A. Your engine will die immediately and will be unable to start because it will have no compression. The camshaft (or camshafts in engines with dual overhead cams) is driven by the belt, so if the belt breaks the cam stops turning and the valves stop opening and closing. However, there is an additional danger if the timing belt breaks.

Some engines are built with very tight clearances between the valves and pistons. If there is not enough clearance between the valves and pistons if the cam stops turning (which is the case in an "interference" engine), the pistons will hit the valves and likely bend one or more valves. This can also cause serious cylinder head and piston damage, requiring replacement of the damaged cylinder head, valves and/or pistons. To prevent his from happening, engines that use timing belts to drive their cams typically have a recommended replacement interval for the timing belt. On most late model applications, that interval is usually 100,000 miles. On older engines from back in the 1980s & 1990s, it was 60,000 miles.

For more information, see Timing Belts: Is Your Engine and Interference Engine?

Q. What Happens If My Engine Blows a Head gasket?

A. A "blown"head gasket can fail one of two ways: The gasket can burn through between cylinders causing a loss of compression and/or it can corrode or fail (often due to engine overheating) and leak coolant into the cylinders.

A compression failure will cause a major loss of power in the affected cylinders, while a coolant leak will lead to rapid engine overheating as well as possible damage to the cylinders, piston rings and engine bearings.

The only fix for a bad head gasket that is leaking compression is to remove the cylinder head and replace the gasket. But if a head gasket is only leaking coolant, there are cooling system sealers that may temporarily or even permanently stop the leak. If nothing else, using a sealer product may buy you some time until you can afford to have the gasket replaced, or sell or trade your car for another.

See Common Causes of Head Gasket Failure.

Q. I Hear a Sharp Pinging Sound When Accelerating. What's Wrong?

A. A pinging or ratting noise that is only head when accelerating is typically a symptom of "Detonation" (also called "Spark Knock"). There is probably nothing mechanically wrong with your engine, but the combustion chambers and tops of the pistons may have a heavy accumulation of carbon deposits that increase compression and combustion temperatures, and cause the fuel to burn abnormally. Cleaning the combustion chambers with a "Top Cleaner" solvent product will usually eliminate the deposits and stop the noise.

Another possible cause of Detonation or Spark Knock can be gasoline that lacks sufficient octane (knock resistance) for your engine. High compression engines, as well as supercharged and turbocharged engines usually require higher octane premium fuel for this reason.

To learn more about Detonation, see Causes of Detonation & Spark Knock

Q. Why is My Oil Pressure Warning Light On?

A. If the Oil Pressure Warning Light is on, it means your engine is not developing normal oil pressure. Low oil pressure is serious because it can quickly lead to bearing damage and engine failure if you continue driving while the warning light on. You should stop immediately, shut the engine off and check the engine oil level on the drip stick.

If the oil level is low, our engine is leaking or burning oil. Add enough oil to bring it up to the full mark and check the engine for oil leaks.

If the oil level is full, the engine may not be getting oil pressure because of a bad oil pump or a plugged oil filter. Oil filters are supposed to have a pressure relief valve so if the filter plugs the oil will bypass the filter. But the bypass may not always work as it should.

Another possibility would be a bad oil pressure sensor or sending unit, or a fault in the warning light circuit or oil pressure gauge.

See Troubleshooting Low Oil Pressure

Q. Is a Turbocharged Engine Better than a Naturally Aspirated (non-boosted) Engine?

A. It depends what you mean by better. A turbocharged engine will make more horsepower and torque than a naturally aspirated engine that has the same displacement and number of cylinders. A turbocharger forces more air (and fuel mixture) into an engine so it can perform like a larger displacement engine. That's why auto makers have been replacing larger displacement V8 and V6 engines with much smaller turbocharged four-cylinder engines. The benefit of doing this is that the turbocharged engine only produces the extra power on demand, which saves fuel when the extra power really isn't needed. So if you drive with a light foot, a smaller turbo engine will usually deliver much better fuel economy than a larger naturally aspirated V6 or V8 engine, while also getting almost the same fuel mileage as a naturally aspirated four cylinder engine of same size.

The downside of a turbo motor is that the turbo and its related plumbing and intercooler add cost to the engine (making a turbocharged vehicle more expensive to buy). Many (but not all) turbo motors also require using more expensive high octane premium gasoline, and a high quality (more expensive) full synthetic motor oil to withstand the extra heat produced by the turbo. And if the turbo fails, they are expensive to replace.

See Turbocharger Diagnosis & Repair

Q. What are the Differences Between Diesel and Gasoline Engines?

A. Diesel engines use the heat of compression to ignite the fuel, so diesels have no spark plugs and no ignition coils. They also have higher compression ratios than most gasoline engines, which improves thermal efficiency for better fuel economy. Diesel engines also inject the fuel under extremely high pressure directly into the combustion chambers of the engine.

Gasoline engines use spark plugs to ignite the fuel, and a throttle body to control air flow into the engine and engine speed. Older gasoline engines used low pressure fuel injectors to spray fuel into the intake ports (Multi-Port Injection), but many late model gasoline engines now use Direct Fuel Injection (like a diesel), and some even use a combination of port and direct injection (essentially two parallel fuel systems).

Because of these mechanical differences, you can't burn diesel fuel in a gasoline engine, or gasoline in a diesel engine. Diesel fuel is actually a slow burning light oil while gasoline is a highly volatile (thinner) liquid with very different combustion characteristics.

Q. Why are Internal Combustion Engines so Inefficient?

A. Gasoline fueled spark ignition engines are only about 30 to 35% efficient in converting the fuel they burn into useful torque and horsepower. Toyota and Nissan have built some high efficiency turbocharged four cylinders that are around 40% efficient. Diesel engines have higher thermal efficiency with ratings typically in the 40 to 44% range. Even so, both types of internal combustion engines waste well over HALF of the energy in the fuel they burn.

Where does this lost energy go? Much of it is soaked up heating the engine itself. Up to a THIRD of the heat energy that is released by burning a gallon of fuel is absorbed and carried away by the cooling system. Were it not for the cooling system, the engine would get hotter and hotter until things started to melt! Another 25 to 30% of the heat produced by combustion is lost as waste heat in the exhaust. A little of this heat energy can be recovered by using it to spin a turbocharger connected to the exhaust, but most of it still goes right out the tailpipe. Internal engine friction also wastes maybe 3 to 5% of the energy produced during combustion.

What's more, internal combustion engines waste 100% of their potential energy output when they are idling when the vehicle is not moving. Stop-start systems that automatically shut the engine off when a vehicle is waiting at a traffic light help eliminate this kind of waste. But the overall gain in fuel economy is only a few percent at best for the average vehicle.

By comparison, electric motors in electric vehicles (such as Tesla and others) are over 90% efficient in converting battery energy into useful power. Tesla says the AC induction motor in the Model S is 93 percent, and some experimental electric motors are approaching 98%. Better yet, electric motors in electric vehicles consume ZERO energy when the vehicle is not moving. They only consume power when the vehicle is in motion.

The reasons why electric motors are nearly THREE TIMES as efficient as internal combustion engines is that they are using magnetic force rather than thermal energy to produce power. Electric motors do generate some heat under load, but nowhere near the waste heat of an internal combustion engine. Also there is only ONE moving part inside an electric motor, the rotor. So only the shaft bearings generate minimal friction to waste energy.

An internal combustion engine, by comparison, has a crankshaft with five main bearings generating friction, plus four to eight or more connecting rods & pistons depending on the number of cylinders int he engine. The piston rings scrubbing against the cylinder walls is a major source of friction, as are all the components in the drivetrain including the camshaft(s), valve lifters or followers, valve springs and valves, and camshaft drive gears, chains or belts.

A four-stroke internal combustion engine also wastes energy compressing the air/fuel mixture, and pushing the spent exhaust gases out of the cylinders. It also wastes energy driving an oil pump (to supply lubrication) and a water pump (to control heat), plus all the other accessories that are driven by the engine such as an air conditioning compressor, and power steering pump (if hydraulic power steering is used). There are additional pumping losses from the restriction created by the throttle plate(s) that limit airflow and engine speed, especially at idle. Add it all up, and you can see why gasoline and diesel engines waste so much of the fuel they burn.

Q. What are the Three Things a Gasoline Engine Needs to Start?

A. Compression, Fuel and Ignition. When an engine is cranked to start it, the download motion of the pistons creates suction in the cylinders to pull air into the cylinders. As the engine's pistons move back up, they create compression which squeezes the air/fuel mixture into a smaller and smaller area. This helps mix the air and fuel, vaporize the fuel and raise its temperature making it more ready to burn. If there is no compression because a broken timing belt or chain is not turning the camshaft(s), which operate the valves, air won't be pulled into the engine and there will be no compression. Same thing happens if the crankshaft is broken, or the crank doesn't turn because the starter or starter drive gear is bad. The engine has to be pumping and compressing air before it will start.

Fuel also has to be mixed with the air before combustion can occur. Whether the engine has port fuel injection or Direct Fuel Injection, fuel has to be delivered into the combustion chamber and mixed with the compressed air to burn. If fuel pressure is low, or the fuel injectors are clogged or dirty, there may not be enough fuel in the air/fuel mixture to ignite, resulting in a no-start. A bad fuel pump, clogged fuel filter, bent or restricted fuel line, or no fuel in the tank can all prevent the engine from starting. Also, the fuel has to be the correct fuel for the engine and not contaminated with water to burn properly.

Finally, there needs to be a spark at just the right moment to ignite the air/fuel mixture in the combustion chambers of the engine. A fouled, badly worn or damaged spark plug, or a weak or dead ignition coil may prevent a spark from occurring. A bad crank position sensor, ignition module or PCM may also prevent the spark from occurring. And in some instances, a fault in the anti-theft system may prevent the fuel pump and/or ignition system from functioning because the ship in the ignition key or smart keyfob failed to send the correct coded signal.

See Diagnosing An Engine that Won't Crank or Start




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Related Engine Articles:

Causes of High Oil Consumption

Engine Oil Leaks

Valve Failures

Diagnose Weak Valve Springs

Understanding Engine Displacement

Compression Ratio: What Is It and How Does It Affect Engine Performance?

Engine Compression Testing

Engine Leakdown Testing

Measuring Blowby

Engine Exhaust Smoke (various causes of)

Finding & Fixing Engine Vacuum Leaks

Engine Overheating: Causes & Cures


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