My cooling system. My 1999 meredes S320 is overheated.

An overheated engine can be caused by anything that decreases the cooling system's ability to absorb, transport and dissipate heat; therefore engines can overheat for a variety of reasons. Let's take a look at some of the most common causes.
Cooling System Leaks
This is the primary cause of engine overheating. Possible leak points include hoses, the radiator, water pump, thermostat housing, heater core, head gasket, freeze plugs, automatic transmission oil cooler, cylinder heads and block. Perform a pressure test. A leak-free system should hold pressure for at least one minute.
Wrong Coolant Concentration
Be sure to use the coolant recommended by your vehicle's manufacturer. The wrong type of coolant and/or mixing the incorrect concentration of coolant and distilled water can also result in engine overheating. The best bet is to perform a complete flush and fill.
Bad Thermostat
A thermostat is a heat-sensitive valve that opens and closes in response to engine temperature. Heated engine coolant passes through to the radiator when the thermostat is in the open position. In the closed position, it prevents the flow of coolant to speed up the warming of a cold engine. When the thermostat gets stuck in the closed position, coolant stays in the engine and quickly becomes overheated, resulting in engine overheating.
Blocked Coolant Passageways
Rust, dirt and sediment can all block or greatly impede the flow of coolant through the cooling system. This can limit the system's ability to control engine temperature, which may result in higher operating temperatures and engine overheating. Once again, a flush and fill is recommended to remove debris.
Faulty Radiator
By passing through a series of tubes and fins, coolant temperature is reduced in the radiator. Leaks and clogging are some of the most common causes of radiator failure. Any disruption in the radiator's function can lead to elevated engine temperature and overheating.
Worn/Burst Hoses
A hose that contains visual cracks or holes, or has burst will result in leaks and disrupt the flow of engine coolant. This can result in overheating.
Bad Radiator Fan
A fan blows air across the radiator fins to assist in reducing the temperature of the coolant. A fan that wobbles, spins freely when the engine is off, or has broken shrouds will not be able to reduce the temperature to proper level, thus possibly resulting in engine overheating.
Loose or Broken Belt
A belt is often the driving link that turns the water pump at the correct speed for proper coolant flow through the cooling system. If a belt is loose or broken, it cannot maintain the proper speed, thus resulting in poor coolant flow and ultimately, engine overheating.
Faulty Water Pump
Known as the 'heart' of the cooling system, the water pump is responsible for pressurizing and propelling engine coolant through the cooling system. Any malfunction of the water pump, including eroded impeller vanes, seepage or wobble in the pump shaft, can prevent adequate coolant flow and result in engine overheating.

Did you have the head checked for warping and crack tested. because combusting gas is finding its way into the cooling system. have you replaced the thermostat .

CHECK COOLANT LEVEL MOST NEWER VECHICLE DONT HAVE RADIATOR CAP YOU HAVE TO POUR COOLANT IN THE COOLANT OVERFLOW JUG THE COOLANT WILL GO TO RADIATOR. IF THE COOLANT OVERFLOW JUG EMPTY ADD COOLANT UNTIL COOLANT LEVEL STOP DROPPING AT STAY AT FULL COLD MARK.IF COOLANT OKAY,NEED TO REPLACE THERMOSTAT AND COOLANT OVERFLOW JUG PRESSURE CAP. IF ALL BEEN DONE. MOST OF THE TIME WHEN CAR OVERHEATING WHILE MOVING. RADIATOR CORES STOPPED UP OR RADIATOR GRILLE DIRTY OR RESRICTED.ENGINE BLOCK COOLANT PASSAGES CLOGGED AND HEATER CORE CLOGGED.CHECK WATER PUMP SEE IF WATER PUMP WEEP HOLE LEAKING IF SO REPLACE WATER PUMP.IF ENGINE OVERHEATING AT A LONG TRAFFIC LINE ENGINE COOLING FANS NOT RUNNING EITHER COOLING FANS FUSE AND RELAYS BAD.OR ENGINE COOLANT TEMPERATURE BAD. THE ENGINE COOLANT TEMPERATURE SENSOR TURNS ON COOLING FANS AT A CERTAIN TEMPERATURE IF SENSOR BAD FANS WONT TURN ON. MAKE SURE YOU HAVE 50 /50 MIXTURE OF COOLANT AND WATER IN COOLING SYSTEM.

First confirm that the engine IS actually overheating - steam, no heat to the interior etc. Sometimes a temperature sensor will fail and give a misleading 'overheat' reading on gauge. For that matter sometimes the gauge can fail and give the same misleading reading. Check that the cooling fan comes on when the engine temperature starts to rise above 'normal'. If not check (in order) fan fuse, fan relay, fan sensor, fan. Real overheating is caused by a lack of coolant AND/OR lack of coolant flow. Modern cooling systems are 'closed'. In other words there should be little or no loss of coolant. If the level is significantly low you have a leak....either external or internal. With the coolant topped up to the correct level and the radiator cap on, run the engine and look for visible leaks...hoses, valves, radiator etc. Internal leaks, eg. head gasket will usually be accompanied by white exhaust smoke (steam), hard starting, rough running and bubbles in the expansion tank. Sometimes, though NOT always, you will find the engine oil has a milky look and/or engine oil will be mixed in with the coolant.

OVERHEATING CAN BE CAUSE BY MANY THINGS LIKE FAULTY THERMOSTAT AND FAULTY RADIATOR PRESSURE CAP,TOO MUCH WATER IN COOLANT SYSTEM NEED 50 / 50 WATER AND ANTIFREEZE.LOOK FOR WATER PUMP WEEP HOLE LEAK, IF COOLANT LEAKING OUT WEEP HOLE WATER PUMP BAD NEED REPLACING.CHECK FOR LOW COOLANT LEVEL, YOUR RADIATOR OVERFLOW JUG SHOULD HAVE COOLANT AT THE FULL COLD MARK IF NOT KEEP ADDING COOLANT INTO COOLANT OVERFLOW JUG UNTIL COOLANT STOP DROPPING AND FULL COLD MARK, IF OVERFLOW COOLANT JUG WAS EMPTY RADIATOR IS LOW ON COOLANT.WHICH CAUSE AIR IN COOLANT SYSTEM KEEPING THE ENGINE COOLANT TEMPERATURE SENSOR FROM BEING SUBMERGE IN HOT COOLANT WHICH TURN ON THE COOLANT FANS.WHEN ENGINE COOLANT TEMPERATURE GET CERTAIN SET TEMPERATURE LIKE 190 DEGREES THE PCM AND COOLANT SENSOR WILL TURN ON COOLANT FANS, IF VECHICLE OVERHEATING COOLANT FANS NOT WORKING EITHER YOU HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR CHECK COOLANT FANS FUSE AND RELAYS. YOU CAN CODE SCAN CAR TO SEE IF YOU HAVE FAULTY PCM, FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR FAULTY COOLANT FAN RELAY.IF COOLANT FAN AND ENGINE COOLANT TEMPERATURE SENSOR OKAY,YOU HAVE CORRECT COOLANT LEVEL IN COOLANT SYSTEM, THERMOSTAT AND RADIATOR PRESSURE CAP BEEN REPLACED, YOU COULD HAVE BLOWN HEAD GASKET CHECK ENGINE OIL LOOKS LIKE MILK SHAKE HEAD GASKET BLOWED ALSO WHEN HEAD GASKET BLOWED YOU CAN DRIVE CAR SHORT DISTANCE START OVERHEATING AND YOU LOOSE ENGINE POWER SUSPECT BLOWED HEAD GASKET.

CAR OVERHEATING FIRST CHECK FOR LOW COOLANT IN THE RADIATOR COOLANT OVERFLOW JUG.IF COOLANT LEVEL IN OVERFLOW JUG LOW REFILL ADD COOLANT BACK TO THE FULL COLD MARK.PUT RADAITOR CAP ON COOLANT OVERFLOW JUG START ENGINE LET IT IDLE UNTIL IT OPERATING TEMPERATURE.MAKE SURE TOP RADIATOR HOSE GETTING HOT WHILE ENGINE WARM UP.IF TOP RADIATOR HOSE DONT GET HOT WHILE ENGINE IDLING YOUR THERMOSTAT COULD BE STUCK CLOSE CAUSING CAR TO OVERHEAT.IF TOP HOSE IS GETTING HOT.CHECK FOR COOLANT LEAKS CHECK TOP RADIATOR HOSE AND BOTTOM RADIATOR HOSE FOR LEAKS.CHECK FOR LEAKS AT THE RADIATOR CORES AND PLASTIC SIDE CONTAINERS.IF ALL IS GOOD ENGINE OVERHEATING WHILE IN A LONG TRAFFIC LINE, COOLANT FANS NOT COMING ON.COULD HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR OR BLOWN COOLING FAN FUSE OR RELAY.COULD HAVE PCM FAULT.MAKE COOLING FAN ELECTRICAL CONNECTORS AND WIRING NOT DAMAGE OR BROKEN.

The most likely causes of a hot running engine are the following:

1. low antifreeze level in the radiator and cooling system.
2. fan not turning on at operating temperature.
3. restrictions in the cooling system such as sediment build up.

Water pumps usually leak when they are bad, and can cause an overheat because of low coolant level.
Check whether the water pump is leaking after topping off the coolant level and running at operating temperature, and then shutting off the car's engine.

When your temperature gauge reaches "H' it may too late to prevent a major breakdown. Knowing the symptoms of an overheated car and how they occur may be the difference between being inconvenienced and incapacitated.
Identification:---Other than a low oil level or low oil pressure light, there is not a more significant part of a car's instrumentation than a rising temperature gauge or a glowing "Hot" light. These lights are really the only confirmation a driver has that his car is really overheating. It is the identification of the symptoms of an overheating car that enable the motorist to avert a badly damaged engine. Overheating is always a traumatic event for a car's engine, which makes the early identification of the symptom an important addition to the informed motorist's tool kit.
Stuck Thermostat:--The car's thermostat is a valve that controls coolant flow from the engine block to the radiator. When the engine is cold the thermostat remains closed so that the coolant can reach operating temperature quicker and also provide heat to the passenger's compartment. The thermostat has a spring on it that moves depending on coolant temperature causing the thermostat to open. Sometimes the thermostat fails to open thus restricting coolant flow to the radiator where it would be cooled down. This condition is often the cause of overheating. The symptoms of this cause would be a rising temperature gauge and possibly the loss of heat inside the car.
Restricted Radiator:---A car's radiator will have thousands of gallons of coolant passing through in its lifetime. Along with the coolant comes particulate matter in the form of corrosion breaking loose from various parts of the car's cooling system. These contaminates collect in the tubes of the radiator reducing its efficiency. Extensive "plugging" in the radiator will cause the car to overheat. The symptom of this condition would be a rising temperature gauge which goes up when you accelerate.
Coolant Loss:--A car's cooling system is a closed loop system. You are not supposed to lose coolant. Sufficient coolant loss will cause the engine to run hot because engine is heating less coolant to higher temperatures. The symptom of overheating induced by coolant loss would be a pool of coolant on the pavement when the leak is external. Steam under the hood as the lost coolant hits hot parts of the engine, or a rising temperature gauge in the case of a undetectable engine related leak. Of course, the gauge would also go up if the leaks were not detected. Deteriorated Water Pump:--Cars use a belt driven pump to push the water and coolant mixture through the cooling system. This part is called the water pump. Rarely the impeller that draws the coolant through the pump will rust away making it impossible to push any through the system. If this occurs the temperature gauge will climb and coolant will boil over in the radiator. Inoperable Fan:----Most cooling fans are electrically driven. Some are driven by fan belts. If a belt breaks or the electric supply to the fan is interrupted overheating may result. Electric fans are tuned on thermostatically when needed. When the car runs at idle for extended periods or the weather is extremely hot, a failed fan will cause overheating otherwise it serves as a standby assist to the rest of the cooling system. In stress conditions an inoperable fan will cause the temperature gauge to rise. This will help. Thanks please keep updated.please please do rate the solution positively .thank you for using fixya

check for low coolant level in plastic overflow resorvoir.There is a float inside which activates this blinking indicator.Do this when vehicle is cool ...contents under pressure

Normal. This is called heat soak. When you stop the engine, its temperature rises since the coolant is no longer being circulated by the water pump through the radiator. The coolant then expands and goes higher in the overflow tank. As the engine cools, it retreats back into the engine. Proper level should be determined only when the engine is cool.