Coolant is being used up quickly and engine keeps overheating.

hi Jonathan.
leaks in your 2005 Volkswagen Beetle. Leaking coolant is one of the more common types of fluid leaks on Beetles. Engine coolant (which is also called antifreeze or anti-freeze) moves through the inside of your Beetle's engine and keeps it from overheating. Coolant can leak from the reservoir or from the hoses, in 2005 Beetles coolant leaks are most likely to occur where the hoses connect to the engine.
A few things to note about coolant is that it is sweet tasting and highly toxic, so it can end up in the dog's stomach pretty quickly. If you ignore a small coolant leak long enough, you will run out of coolant, which leads to an overheated engine and other serious, but highly avoidable, problems. In many 2005 Beetles, an anti-freeze leak can cause the temp sensor to record high engine temperatures. thermostat most likely culprit if it is taking a long time to heat up.
or read up some more at this link.

2005 beetle heater takes long time to heat up Google Search
or this one.
2005 beetle leaks coolant somewhere Google Search

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.

Temperature Warning Light is on Inspection Service How this system works: With the exception of older, air-cooled vehicles, cars rely on a liquid called coolant (or antifreeze) to keep the engine at an optimal temperature. Coolant is a mixture of water and ethylene glycol, and it circulates around the engine block and absorbs excess heat, which keeps the engine from overheating. The coolant converts that heat to air in the radiator, and then the air is emitted, at which time the coolant is ready to absorb more heat. Without coolant, the engine would quickly ruin itself with its own heat production. Common reasons for this to happen:

• Coolant is low or weak: The most common culprit when an engine overheats is low or weak coolant. If your car doesn't have enough coolant, then it can't absorb enough heat. While your car will naturally lose small amounts of coolant over the years, a leak is the most likely cause of low coolant levels.The proper ratio of coolant to water can also get distorted, resulting in a problem. Too little or even too much antifreeze can dramatically lower the boiling point of the coolant. A proper ratio of antifreeze to water is 50/50 to 60/40, depending on the vehicle.
• Broken radiator fan shroud: The radiator fan shroud directs the airflow across the radiator so the air can absorb the coolant's heat. When the fan shroud breaks or becomes dislodged, air fails to enter the radiator, and the coolant will no longer have a place to direct the transfer of heat.
• Broken or missing air dam: Along with the shroud, some vehicles have an air dam (or deflector) underneath the vehicle. If this is broken or missing then the air can pass underneath the vehicle but not also through the radiator, which will cause overheating. These air dams are essential in newer vehicles, as they force the air through the fan shroud.
• Faulty coolant temperature sensor: The temperature sensor takes constant readings of the coolant temperature and sends that information to the engine control unit. Based on the temperature of the coolant, the engine control unit adjusts the ignition timing, the fuel injector pulse, and the operation of the electric cooling fan.
• Bad water pump: The water pump is responsible for keeping the coolant cycling throughout the engine. After the coolant transfers its heat energy to the air, the water pump recirculates it around the engine so that it can absorb more heat. The most common water pump problems are a leaking pump, bad bearings, or an impeller that has rotted away due to a low coolant ratio.
• Stuck thermostat: The thermostat acts as a dam for the coolant. When the engine first turns on, and it is still cold, the thermostat keeps the coolant from circulating, which allows the engine to warm up as quickly as possible. Once the engine has reached its operating temperature, the thermostat opens and allows the coolant to circulate. A stuck thermometer may stay permanently sealed and therefore keep the coolant from reaching the engine block.
The thermostat may also stick open. This will not usually result in overheating, but it will waste gas.

• Broken engine cooling fan: The engine has a cooling fan that is deployed when the coolant needs some extra help. When the coolant temperature sensor notices that the coolant temperature is getting too high, the engine control unit (on newer vehicles) will initiate the cooling fan to reduce the temperature.
• Broken thermostatic fan clutch: Older vehicles use a thermostatic fan clutch to engage the engine cooling fan, which is mounted to the fan blades. The fan clutch uses a bi-metallic spring that tightens when the temperature increases. This acts as a "high speed" option for the fan, and when engaged, it draws more air across the radiator.
• Blown head gasket: The head gaskets sit between the engine block and the cylinder heads, and keep coolant from entering the engine's oil and combustion chamber. When a gasket blows and coolant seeps in, the issue is not only that the engine will overheat, but also that damage may be done to the catalytic converter and oxygen sensors due to contamination from the coolant. What to expect: A top-rated mobile mechanic will come to your home or office to determine the cause of the temperature warning light turning on and the source of the overheating, and will then provide a detailed inspection report that includes the scope and cost of the necessary repairs. How important is this service? An overheating engine is extremely dangerous. It is not safe to drive a vehicle with an overheating engine, or you may ruin the engine completely and put yourself at risk. As soon as you notice the light come on, pull over. If there is no place to safely pull over, turn off your radio and other electrical units, and turn your heat on high (this will funnel some of the hot engine air into the cabin). As soon as you can safely pull over, do so, and then book one of our mechanics to perform an inspection.
  

get it serviced

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.

FIRST OF ALL CHECK ENGINE COOLANT LEVEL IF LOW YOU NEED ADD MORE COOLANT CHECK FOR LEAKING TOP AND BOTTOM RADIATOR HOSES, CHECK RADIATOR FOR LEAKS. IF YOU DID NOT LOSE MUCH COOLANT THERMOSTAT COULD BE STUCK CLOSED.WHEN ADD COOLANT CRANK VECHICLE AGAIN CHECK BOTH RADIATOR HOSES THEY BOTH SHOULD BE HOT. IF TOP RADIATOR HOSE GOING TO ENGINE BLOCK COLD AND BOTTOM RADIATOR HOSE COLD WARM THE THERMOSTAT IS STUCK CLOSED. IF ENGINE OVERHEATING WHILE SITTING IN LONG TRAFFIC LINE YOU COULD HAVE FAULTY ENGINE COOLANT TEMPERATURE SENSOR.IT CONTROLS COOLANT FAN AT SET TEMPERATURE.IF COOLANTS FAN NOT RUNNING WHEN OVERHEATING.EITHER COOLANT FAN FUSE RELAY FAULTY OR FAN MOTOR DEFECTIVE OR FAN MOTOR WIRING CONNECTOR HAVE BROKE WIRES.IF COOLANT FAN IS RUNNING WHILE ENGINE OVERHEATING CHECK CRANK OIL AT OIL DIP STICK OIL LOOKS LIKE MILK SHAKE YOU HAVE BLOWED HEAD GASKET. WARNING DONT KEEP DRIVING VECHICLE WHEN ENGINE OVERHEATING YOU WILL CAUSE ENGINE AND TRANSMISSION DAMAGE.

Overheating can seriously damage a car's engine if left unchecked. Although overheating simply means that a car's engine temperature exceeds normal operating temperatures, the causes of overheating are varied. What follows is a brief list of some of the most common causes of engine overheating.

Faulty Radiator
1. A car that overheats will often have a faulty radiator. A radiator is responsible for cooling hot engine coolant that picks up heat from inside a car's running engine. A radiator "radiates" the heat from engine coolant out into the outside air. A faulty radiator loses its "radiating" effects and allows engine coolant to become overheated, thus rendering it ineffective at adequately cooling and engine.
Faulty Water Pump
2. A faulty or malfunctioning water pump prevents adequate engine coolant flow and can cause a car to overheat. A water pump serves to pressurize and propel engine coolant throughout a car's engine and radiator to increase the heat-reducing capabilities of engine coolant. A faulty water pump loses its ability to adequately pump and propel engine coolant, and can cause a car to overheat.
Coolant System Leaks
3. A leaky engine coolant system reduces the level of circulating engine coolant, which increases engine temperature and leads to engine overheating. Radiators, water pumps, and coolant system hoses and seals--all of these coolant system parts can develop leaks, which can result in low coolant levels and engine overheating.
Faulty Thermostat
4. A car thermostat regulates the flow of engine coolant. A thermostat is a heat-sensitive valve that opens when a car engine reaches a set operating temperature and closes when a car engine is cold and warming up. If a thermostat gets stuck in the closed position, coolant will be prevented from reaching the engine, which will quickly lead to engine overheating and potential engine damage.
Low Engine Oil Level
5. Engine oil, in addition to lubricating an engine's internal parts, helps to keep engine operating temperatures reduced by eliminating friction within the engine. If engine oil levels are low, friction and heat build up inside an engine, a condition that causes increased engine operating temperatures and can lead to engine overheating.

1. The thermostat in the cooling system could be sticking and need replacing. If it sticks in the closed position coolant cannot flow to and from the radiator and the coolant circulating through the engine will quickly overheat.

2. The water pump may be on its last legs and require replacing. If the pump has failed (and they do) the coolant will not circulate through the engine and radiator as it is designed to do and it will overheat quite quickly.

3. There could be a build up of debris in the cooling system that is impairing coolant flow through the engine. This can occur if the cooling system is not fully flushed out every 2 years and the coolant replaced. The cooling system must then be bled to remove all air. When replacing the coolant you MUST use the correct product as specified by the manufacturer and in the correct mix.

4. Radiator caps must be sound (and the correct specification) to ensure coolant does not escape and result in a low coolant condition and then overheating.

You need to get your car to a competent mechanic quickly to check and rectify the problem. (You may find it is only the thermostat as this is a common problem with time and usage.) Driving your car with an overheating condition WILL result in expensive engine damage. The head gaskets will blow and the heads on the engine will crack. Additional engine damage is also possible.

Cooling systems must be well maintained to prevent overheating and consequential engine damage.

Any cooling system fault in JULY/AUGUST is a big deal. This sensor is 22$ and can be installed in a COLD engine in minutes.Very small cost for accurate gauge so you can monitor gauge and know if real overheating conditions exist.I would probably spring for a new thermostat while Im servicing that sensor and coolant just for good measure. stay cool