Internal Combustion Engines make their power through a series of controlled explosions between fuel and air. That and the inherent friction found in any moving series of parts generates heat. Lots of it. Enough to warm the car and you on a sub zero winter's day. But that heat must be managed or the motor will melt down. Engine Cooling systems are designed to take away that heat.
The first is the Engine Lubrication system. Surprised? You shouldn't be. I remember an engineer who once told me, "Oil cools the engine. Water cools the oil." The engines lubrication system is the motor's first line of cooling, and in air cooled cars like the porsche 911, the classic Franklin automobile or the original Volkswagen Beetle oil does most of the work. In a resting engine, oil is stored in the oil pan, which contains between four and five quarts (liters) in most automobiles. An oil pump of several types will rest in the base of the pan, and will pump oil up to the cylinder head, main bearing journals and other parts of the valve train, where gravity will ultimately return it to the pan. All this oil moves through a series of oil galleys, that pass through the engine much as arteries, capillaries and veins carry blood throughout the body. Loose oil will also be scooped up by probes attached to the piston rod bearing caps, to lubricate the rod bearings. In high performance engines a windage tray my rest between the base of the pan and the bearings to ensure oil is up for the rods to catch. There may also be some type of baffle to ensure that oil gets tot he pump. High performance or heavy duty motors are often equpped with an oil cooler, really a small radiator to help the oil shed heat. Oil coolers are rarely installed in street cars because they represent additional cost and something else that might break. Things that leak oil are very, very bad.
Maintaining the oil system.
First of all, check your oil regularly. You do this by lifting the hood and locating the engine dipstick. Cars with an automatic transmission will have a second dipstick for transmission fluid. The engine dipstick should be marked, and may be co-located with the oil filler neck. If you have two dipsticks, the oil stick is usually forward of the transmission dipstick, and sticks into the engine, not the transmission.
With most cars the engine should be checked cold because the heads will contain a lot of oil during normal operations, making an accurate reading difficult. Some, like my truck, are designed to be checked hot and the dipstick scaled accordingly. You remove the dipstick, wipe it clean with a towel and reinsert it fully. The second withdrawal is when you read, because cleaning the dipstick removes any oil that may have splashed upon it. There will be a full line, and every 1/4 inch below that line approximates one quart of shortfall. If the engine is full, put the stick back in. If not add oil, but be careful not to overfill. Overfilling will cost you power as the rods and crankshaft have to fight their way through the excess oil. Reading the dipstick will give you a good idea of how much to add.
Oil MUST be changed regularly. As oil flows through the engine it also carries away much of the dirt-- and other bad stuff-- that comes with running the motor. Heat will break oil down over time. The old rule used to be change the oil every 3 months or 3,000 miles, whichever comes first. That isn't a bad rule. No engine ever died from too many oil changes. However, the consensus among the automotive press is that 5-6,000 miles is a reasonable interval given the advances made in producing conventional oils. Synthetic oils last longer and reduce friction, but cost from three to five times as much.
If you wish to change your own oil, you can, and this will save you money at the cost of time. First of all, elevate the car so you can reach the oil pan drain plug and oil filter. The car MUST be resting on securely mounted jack stands before you risk crawling underneath it. Violating that rule kills people every year, and being crushed is a slow and painful way to go. No, the car may not be simply jacked up. Jack stands under all four corners is the ONLY way to go. Otherwise have a pro change your oil.
Having put the car on stands you will need a wide oil pan, which you will place under the drain plug. Keep shop rags handy. Select the correct sized open end wrench for your car and loosen the oil drain plug, which will be located at the base of the oil pan. Once loose you will notice that oil begins to flow out after only a few threads have been loosened. Keep loosening it until the plug is removed. Then go get a sandwich and let the oil drip out until it finally stops. When the oil stops, replace the drain plug, making sure it is tight. Move the pan under the oil filter. Use your oil filter wrench unscrew the oil filter, and then empty it into the pan. It will be full of oil, and is full of passages so that will take some time. If you have a screen, just put the screen on top of your drain pan and set the filter on it, upside down, so it will drain. When done pour the old oil into a container, so it can be recycled. Any auto parts store will accept your old oil, for free.
Next take a new oil filter that was designed for your car. The correct filter is easily found, guidebooks for each make, model and engine are found at every auto parts store. Take a quart of oil, and begin to fill the filter with oil. Pre-filling the oil filter gets oil to the engine quicker when you restart it, reducing wear. This will also take some time, which explains why your local service station does not pre-fill the filter. The same oil passages that make your old oil filter slow to drain, will make this one slow to fill. But take your time, after all, your car is worth it. While refilling it, moisten the little rubber gasket on the filter with oil, this will help the new filter seal without getting it too tight. Then reinstall the filter, making it nice and tight. Once that is done add the recommended amount of oil, minus the oil you have already put into the filter. Close up the filler cap, then check the oil to make sure you're full before you're ready to take down your car and drive.
A note about oil.
Viscosity is a measure of the oil's thickness. All things being equal, the higher the viscosity the more effective oil is as a lubricant. But the higher the viscosity, the more resistant the oil is to being pumped where it needs to go. That costs power by increasing resistance to the oil pump. Which is why most cars get a multi-grade motor oil. Most cars use a 10W30 oil which means it moves like a ten weight oil in Winter (10W) but is a 30 weight the rest of the time. Single grade oils are fine in summer, and 40 and 50 weight oils are for high performance or racing applications. Street cars can use multigrade all the time.
Synthetic oils are a significant advance. They are more effective at reducing friction than standard oils-- a 30 weight synthetic is roughly equivalent to a 50 weight petroleum product. Plus they are more stable at temperature extremes, and much less prone to thermal breakdown. Double the mileage between oil changes. Users of synthetic oil can also expect a 1% bonus in both power and fuel economy. But they are not a panacea. Synthetic oils are much more expensive, up to 500% more money. Plus the oil molecules are much smaller than in standard oil. That smallness helps them do their job, but if you car has any tendency to leak oil synthetic oils will exacerbate the leakage. In fact, a car that does not normally leak may start.
The water cooling system
Now we get to the part you were expecting all along. The part where "water" is pumped through the motor for cooling. The block and heads are honeycombed with a series of water journals that absorb the excess heat and carry it away from the oil. Coolant exits the engine through the top hose and is transferred to the radiator. A radiator is essentially a long hollow tube that is loaded with heat sinks. The radiator will have a drain hose linking it to the surge tank, an auxiliary tank that holds coolant that may be sucked into the engine if needed, or where overflow may be stored. Having passed through the radiator coolant returns to the engine through the bottom hose (remember heat rises, cool sinks) which is connected to the water pump, which is one of the accessories driven by the serpentine belt. The water pump moves coolant throughout the engine until it returns through the top hose.
The amount of water entering the engine is controlled via a thermostat, which is generally located under the fitting that connects the top hose to the engine. The thermostat is a very critical device. If the thermostat locks closed, the engine will overheat. If it sticks open, then the engine will never come up to operating temperature, and operate efficiently.
Modern engines require the thermostat to operate properly if the engine is to do its job. Engines are run hot--- 210 degrees not an unusual temperature-- to ensure efficient combustion and reduced emissions. Sudden drops in gas mileage and/or power may be traced to bad thermostat. Pay attention to your temperature gauge, if you have one. If you engine seems to be operating poorly, and the operating temperature seems odd, your thermostat is possibly the culprit.
Modern engines pressurize the coolant, Pressurization raises the boiling point of the coolant. A coolant system is tested in two ways. A pressure test is used to find leaks. Second, the coolant itself may be sampled. Sampling can tell you if the coolant is leaking. It can also detect a blown head gasket if combustion products are detected in the coolant. Overheating may be the first sign of a head gasket problem.
The easiest way to maintain your cooling system is to check the coolant level. This is done with the engine cold. Usually monitoring the surge tank, which has a fill line, is enough to check coolant level. If it is low, open and fill to the line. If it is empty, and the engine is cool, remove the radiator cap and add coolant. Start the engine, if the radiator is low, as the system cycling will lower the coolant level. Keep filling until the coolant level stops dropping, then carefully close the cap. While doing this inspect your hoses for cracks. If you find any cracking, replace the hose because it's about to break. Hoses are cheap, a lot cheaper than a tow, and much less a blown engine.
Do not open your radiator cap when the engine is hot. You may be badly burned by boiling coolant.
Do not add coolant to a hot motor. The temperature differential may crack the radiator. However coolant may be added to a partially full surge tank.
Coolant consists of anti-freeze and water, normally mixed at a 50/50 ratio depending upon climate. The type of coolant will be listed in your car's owners manual or service manual as will the change intervals. Modern coolant can be good for 100,000 miles, longer than cars used to last. Usually the old coolant is pumped out and replaced with water in a procedure called "flush and fill", which also removes things like calcium from the cooling system. Flushing is a good thing to do when the coolant reaches its replacement interval.
A properly operating coolant system, topped off with good oil and water is very important to insuring the long life of your engine. This is not the place to scrimp. Spending money here will save you money down the road.
Air-cooled engines
Water cooling is not a requirement for a successful automobile engine.
Franklin automobiles did away with the radiator, and enjoyed a fine reputation in the early days of motoring. The first
Volkswagen Beetle,
Porsche Speedster,
VW Microbus and the early
Porsche 911 all used airflow over the engine to cool the motor. Air cooling enjoys many advantages. First of all the engine can be much simpler, with no need to cast water journals in the block and heads. The engineer gets to do away with the radiator,
water pump, hoses, thermostat or to worry about water
freezing inside the engine. That all gets rid of a number of problem areas, cuts costs and reduces weight.
But air cooling is not a panacea. First of all, you have to ensure sufficient airflow over the engine. That's fairly easy at highway speeds, much harder in a rush hour traffic jam. The engine must be designed in order to ensure airflow, and that affects its shape, which in turn affects the shape of the car. The horizontally opposed layout of early VW and Porsche engines is in part to ensure cooling, but also mandates a very wide engine. An inline engine is necessarily very long.
But an even more severe issue is temperature regulation. Most engines work best at an optimal temperature. Ambient temperatures do affect both horsepower and gas mileage even in water cooled cars. Air-cooled cars are even more affected by temperature changes, simply because the thermostat makes controlling operating temperature much easier. Water cooling also makes it much easier to heat the passengers. Anyone who has ever ridden inside and old Beetle in winter can tell you how poor the heaters were. A lot of people who were otherwise happy with their bugs bought a different car next time in order to get a decent heater.
An aside
The United States Army has good results and never, ever changes their engine oil. The Army's attitude is that the problem with oil isn't that it wears out, but rather that oil gets dirty. What the army does is change the oil filter at regular intervals. That does replace some engine oil, as a good bit is stored inside the filter. At the same time they take a sample of oil for analysis. A tech examines the oil under a microscope for metal shavings, unexpected particles and other signs of stress. If something questionable is found, nothing happens then. If the next scheduled test also shows a potential problem the engine is torn down.
The Army has learned that because the oil circulates everywhere, unwanted bits in the oil are early signs of trouble. They save on oil costs, and save again because they often catch a budding engine failure early. That saves a lot of money because a minor rebuild is much cheaper than a new engine.
Of course you and I probably don't have the lab and expertise required to do this. And the Army is wrong, engine oil can fail, particularly the organic stuff. But oiil failure is almost always a product of excessive heat, which the Army's preventative maintenance procedures do much to prevent. You and I should continue changing our oil on schedule. But fleet operators may wish to follow the Army's example.