Vehicle Information:?

Volkswagen Jetta 2.5L 2005-2013 
Volkswagen New Beetle 2.5L 2006-2014
Volkswagen Golf 2.5L 2010-2014
Volkswagen Rabbit 2.5L 2006-2009
Volkswagen Passat 2.5L 2012-2014

What is a Car Thermostat?

A thermostat opens or closes a valve to control coolant flow between the car's radiator and engine. It responds to changes in temperature. The valve itself operates through a wax-container element. As coolant temperature increases, the fluid (or wax) container melts and enlarges, which, in turn, pushes a small bar, dividing a centre plate from its mounting base to expose the valve. The thermostat also helps to keep your engine running smoothly and reduces engine wear. Ensuring optimum fuel economy and harmful emissions.

If your car starts overheating quickly after starting it, or the dashboard temperature gauge drops below normal, it might be an indication that your thermostat has failed.

What is a Thermostat Housing?

The thermostat housing is where the thermostat is fitted to perform its operation. A broken housing might cause the thermostat to fail, which, in turn, could cause damage by overheating your engine.

How a Car Thermostat Works

Sitting between the engine and the radiator and usually connected to the upper or lower radiator hose, think of the thermostat as a valve that opens and closes to allow or prevent coolant from flowing to the radiator.

All thermostats have a temperature rating at which they open or close, and the rating can differ from vehicle to vehicle based on the manufacturer's specifications. Most thermostats are rated to begin opening between 180 and 195 degrees and will reach the full open position around 20 degrees higher, allowing coolant to flow between the radiator and engine.

Problems a Thermostat Can Experience

The thermostat isn't a maintenance or wear-related item that requires replacement at any pre-set level. Instead, it's usually only replaced if failing, or whenever the water pump is replaced. The main problems a thermostat can experience are being stuck open, stuck closed, or leaking.

1. Thermostat Stuck Open

If the thermostat is stuck open, an optimal engine temperature is never going to be reached, and there will be no or little heat available in the passenger compartment, and engine wear can increase.

2. Thermostat Stuck Closed

If it's stuck closed, the engine is going to overheat because coolant isn't moving to the radiator. Debris or a broken spring in the thermostat could be responsible for it being stuck in either the open or closed position.

3. Leaking

Finally, the thermostat housing can fail and begin leaking coolant.

Signs of a Bad Thermostat

At the very least, a periodic visual inspection should be conducted under the hood and under the car to look for signs of leaking coolant. Another alternative is to actually test the thermostat by removing it from the vehicle and placing it in a pot of boiling water. If the thermostat opens in the water, and then closes when removed from the water, it's working. Other warning signs indicating a faulty thermostat include:

1. Fluctuations in engine temperature (This could also indicate there's an air bubble in the system that can be removed by bleeding the cooling system.).
2. “Check engine light" is illuminated with an OBD code indicating it's thermostat-related. There are multiple codes that could indicate a thermostat problem, such as P0128 or P0125.
3. Engine overheating.
4. No heat or little heat in the passenger compartment.
5. Engine runs rough or there are fluctuations in engine performance.

How to Replace a Vehicle Thermostat?

What You'll Need

• New thermostat;
• Thermostat gasket;
• Coolant/antifreeze;
• Jack;
• Jack stands;
• Drain pan;
• Ratchet & socket set;
• Pliers;
• Gloves;
• Shop towels;?

Pro Tip

Take a look at the coolant/antifreeze first. If it looks dirty, it should be flushed. It would be a good idea to flush with the old thermostat still in, or removing it to complete the flush.

Installation Steps:

1. Let the engine completely cool down. Pop the hood.
2. Depending on the vehicle, you may need to raise the front end using a jack and jack stands. Set a drain pan under the engine.
3. Drain the cooling system through the radiator drain valve, or by removing the lower radiator hose. Store the coolant for later recycling or disposal.
4. Following the radiator hose to the engine, disconnect the hose clamp, and pull off the hose.
5. Remove the thermostat housing cover bolts, and lift off the housing. (Note that some newer vehicles use a thermostat/housing combo.)
6. Note the orientation of the thermostat, and how the new one will be mounted. Compare the old and new thermostats closely to be certain you've got the right part.
7. Remove the thermostat and clean the sealing surface, using a gasket scraper.
8. Install the thermostat gasket and ensure correct alignment.
9. Place the thermostat into the engine. The deeper spring-side end goes into the engine, while the shorter end sits in the housing. If there is a tab, it goes through a slot in the thermostat flange. If the thermostat doesn't sit flat, it's incorrectly installed.
10. Replace the thermostat housing, then the housing bolts. Torque to 15 lb-ft. (No torque wrench? This is about the same force as needed to twist open a bottle cap.)
11. Reattach the radiator hose and hose clamp.
12. Lower the vehicle and refill the cooling system. Start the engine and monitor the coolant level, being sure to get out any air bubbles. To ensure air is removed from the system, run the engine for about 10 minutes with the heat on.
13. Take a test drive and watch the engine temperature to confirm your repair, and then after a couple of days, check the coolant level. It's normal for the reservoir to need a little top off.

FAQs About Thermostat

Q: Why Should You Replace a Bad Thermostat?

A: Aside from maintaining the engine’s optimal performance, getting a new thermostat reduces the risk of overheating and thermostat failure. Experts recommend changing the thermostat every ten years for preventive maintenance, especially on early-model and high-mileage vehicles.

Q: Can You Drive Without a Thermostat?

A: It is not advisable to run your engine without a thermostat. While driving without a thermostat almost never causes overheating, it does increase the risk of sludge formation due to the engine running too cold, and sludge in the oil pan can starve the engine for oil.

Q: Is it Safe to Drive with a Bad Thermostat Housing?

A: Although it’s possible to drive with a damaged thermostat housing, it’s highly recommended that you don’t. Ignoring a coolant leak is flirting with disaster, and cooking your engine can ruin your whole day. It’s best to enlist the help of a mechanic to check your thermostat and replace the faulty parts as needed. You don’t want to wait until your vehicle overheats, potentially causing catastrophic internal engine damage.