Unless you drive an old German air-cooled car (Porsche or VW), chances are you'll have to tend to the cooling system of your vehicle someday. Here's a How To... on maintaining and repairing your car's cooling system.
Before we get into the why's and wherefore's of maintaining your vehicle's cooling system, let's spend some time reviewing what the system does and how it's designed. Then we can explore ways to care for and maintain it.
Internal combustion engines create friction. Even with the best motor oils, which help to reduce the friction by making everything slippery so that the internal components slide past one another with a minimum amount of resistance, the engine still produces a vast amount of friction. Friction creates heat, the enemy of engines far and wide. It is the job of your engine's cooling system to get rid of that heat as quickly and efficiently as possible.
The basic components of your car's cooling system include a radiator, fan, water pump, thermostat, a sensor or two, an overflow tank, water, coolant, and a series of belts, clamps and hoses to connect it all together and make it run. The system works by directing fluid past the hottest parts of your engine (the cylinder heads and valves), then redirecting that fluid out to the radiator, where the heat collected from the cylinder heads gets dissipated into the cooler atmosphere. Then the whole process begins again.
Before we get into each component, here's a short seminar on coolant. The fluid within your car's cooling system contains both water and coolant. The coolant portion consists of a green fluid that contains ethylene glycol. This chemical extends the freezing and boiling point of water, making it ideal for use in automotive radiators; it also inhibits rust, an added bonus. For most climates, we recommend a minimum 50-50 mix of coolant to water. In other words, if your cooling system holds two gallons of fluid (see your owner's manual), it should contain at least one gallon of coolant (convenient, since it comes in one-gallon containers). For more severe climates, you can increase this percentage to about 70 percent, at which point the benefit stops.
(An important note of caution here: NEVER open your cooling system to add fluid when the system is still warm. Best to let it cool overnight. Not only are the contents scalding hot, they're also under incredible pressure.)
Now onto the other components. The radiator, generally made of aluminum, sits just behind the front grille of your car. It consists of a series of tubes (known as the radiator core) which contain the above-mentioned coolant/water combination. Attached to these tubes are thousands of little metal (also aluminum) fins. These fins effectively increase the surface area of the radiator, exposing the heated fluid within to the cooler surrounding air. The heat gets whisked away by the atmosphere.
A fan is bolted to the inside of the radiator. In the old days, this fan, driven by a belt off the engine, ran all the time. Because of improvements in coolant technology and engine efficiency, the fan is now electric and runs intermittently, kicking in only when you need it. Park your car in your driveway on a hot day, leave the engine idling, and watch the water temperature gauge rise. When it gets to about halfway, the fan will kick in. A heat sensor did that. The fan serves to increase the volume of air moving past the little fins. Watch it now — see the gauge drop! Since a car traveling at 60 or 70 mph has its own built-in airflow system, it doesn't need a fan going all the time. Removing this drivebelt reduces the load on the engine and improves mileage and efficiency (hey, every little bit helps).
The water pump drives the coolant through the system. Pumps come in several varieties, but are generally a centrifugal type, with a rotating impeller. They're driven by a pulley off the engine.
The system also includes a thermostat, which senses temperature and controls fluid flow within the system, a plastic overflow tank, which serves as a reservoir for excess coolant (remember, heat expands things), and the aforementioned hoses, clamps and belts.
So what can go wrong? Well, a lot of things.
For one, the system can spring a leak. If you notice that your vehicle is running warmer than usual, park it, turn off the engine, and look underneath. Do you see a greenish-looking fluid on the ground underneath your car? If so, open the hood. Any funny noises? A leaky cooling system on the boil will make a distinctive whistling sound, like a teakettle getting ready to scream. Remember, the system's under pressure: if there's a leak, you should be able to spot — or hear — it. Or smell it. Radiator coolant, when atomized into steam, casts off a characteristic aroma you're not likely to forget once you've smelled it. A little sulfurous — like the last time you visited Carlsbad Caverns. No leaks? OK, you're not out of the woods yet. Get a rag and carefully open the lid to the plastic overflow reservoir. Look inside it. If there's fluid in there, you may have something more serious going on with the engine. If not, and you don't smell or see or hear a leak, you need to explore further. If you're close to home or your mechanic's shop, close the hood and gently nurse your baby in that direction, or at least to a place where you can investigate further? Keep a close eye on the water temperature gauge as you drive.
A little dissertation on heat. We mentioned earlier that heat is the enemy of your engine. If you're getting indications from your instrument panel that your car is running way too hot, or if you see or hear or smell something indicating excessive heat, it generally means one of two things. Either there is something seriously wrong with your engine, or the cooling system isn't doing its job properly. Either way, you have to be very careful about driving the vehicle until you solve the problem. An overheated engine is a severe problem. If you're driving your car and your water temperature gauge goes, and stays, in the red for any length of time, you must pull over immediately and have the car towed. Trust us, if you're not careful, a $10 repair can end up costing you thousands.
You've made it home, your car is running all right, just hot, and you don't have water coming out of your tailpipe, which means you probably don't have a blown head gasket. If the car is not running dangerously hot, and you want to troubleshoot the problem yourself, park it in the drive, but leave the engine running. Now watch the water temperature gauge to see if it rises. If it gets near the red and the fan doesn't kick in, you most likely have a bad sensor. Turn off the engine and let it cool, find the wire that runs from the fan to the engine (best to disconnect the battery first), and remove the sensor. Have a buddy take you to the auto parts store and buy a new one (usually less than 15 bucks). Install it and run the test again to see if the fan kicks in this time. Does it run? Is the temperature dropping? If so, everything's probably OK.
If this doesn't fix the problem, or if the fan kicks in but the temp continues to climb, you may have a bad thermostat. The thermostat resides under the return hose that runs from the engine back to the radiator; this hose usually comes off the top of the engine. Let the engine cool, remove and replace the thermostat, then run the idling test again. If that doesn't fix it, you'll have to check out the water pump or the radiator. (Don't overlook the thermostat, though. We recently replaced one after a new radiator and fan sensor, and it fixed the problem. Total price of the thermostat: $4)
These are a few of the basic things you can do to maintain your cooling system. If all this hands-on stuff scares you, take the car to your mechanic. Most cooling system problems can be fixed for under $300.00.
Remember, though, never drive a seriously-overheating car. It can cost you thousands.