The Thermostat Is Leaking on My 2001 Jetta VR6

The automotive thermostat functions as monitor that regulates the amount of coolant that flows from the radiator into the engine coolant passages. When the 2001 Volkswagen Jetta VR6 engine is cold, the thermostat diaphragm, which functions like a valve, remains closed to allow the engine coolant to heat up. Once the thermostat reaches a certain operating temperature, it opens and stays open to allow cooled radiator water to enter the engine. A leaking thermostat in a 2001 Volkswagen Jetta VR6 can be the result of a few problems, which the owner can diagnose and repair.

Instructions

1

Park the vehicle on a level surface, and place the selector in park or neutral, depending upon your transmission. Set the emergency brake and raise the hood. Use a socket and wrench to disconnect the negative battery cable from the battery. If the engine is hot or warm, turn the radiator cap a quarter or half turn counterclockwise, or lift up the pressure release lever. Let the engine cool.

2

Raise the vehicle with a floor jack and place two jack stands under the rear part of the frame and two under the front frame section. Place a drain pan under the radiator drain plug location, or under the bottom radiator hose. Depending upon your preference, remove the drain plug with a socket, or use a screwdriver to loosen the radiator hose clamp and pull the radiator hose free.

3

Drain enough coolant from the radiator to permit the coolant level to drop below the height position of the thermostat, then install the drain plug and tighten it, or reconnect the hose and tighten the clamp with a screwdriver. Place the drain pan under the thermostat location, which is at the end of the cylinder head on the Jetta VR6 engine. Notice if the hose connection to the flange leaks, or if the thermostat housing seal leaks. If the hose clamp looks loose, tighten it with a screwdriver to stop the leak.

4

Loosen the upper radiator hose clamp with a screwdriver and pull the hose end free if you suspect a housing leak. Remove the two metric housing bolts with a metric socket. The bolts face up, so you can use a socket and wrench in an upside down position from the top, or use a socket extension to reach up to the bolts from underneath the vehicle. Pull the housing free.

5

Inspect the thermostat housing for cracks on the outside edges and at the bolt hole locations. Any cracks in the housing indicate a defective housing, and you will need to replace it with a new one. If no cracks are seen, use a gasket scraper and wire brush to clean the engine mounting surface and the mating surface of the thermostat housing. Remove all gasket material or any sealant or silicone with a wire brush and carburetor cleaner.

6

Place a straight-edge ruler across the mating surface of the thermostat housing. Run the ruler back and forth from all angles. If you see any dips or irregularities that suggest metal warp, set the housing between the jaws of a vice with the mating surface facing up. Do not over-tighten the housing in the vise.

7

Use a fine-tooth flat file to gently file across the housing mating surface, moving the file around in a 360 rotation. Shave enough metal from the mating surface so it appears shiny on all lip areas. Clean the filings away with a rag and carburetor cleaner. Clean the housing bolts with a small wire brush and lubricate them with anti-seize lube. If you want to replace the thermostat at this time, set the new thermostat inside the housing, with correct face upward, as indicated by the stamp on the diaphragm. Set the new O-ring inside the groove.

8

Place and align a new gasket on the thermostat housing. Install the thermostat housing on the engine block and insert the housing bolts by hand, as far as they will go. Use a socket and wrench and tighten the housing bolts. Use a torque wrench to tighten the bolts to 7 foot-pounds. Reconnect the radiator hose to the housing flange and tighten the hose clamp with a screwdriver.

9

Fill the radiator with a 50 percent ratio of water to coolant. You can also reclaim and refill the radiator with your old coolant, provided it looks clean and is free of contaminants. Reconnect the negative battery cable and start the engine. Keep the radiator cap off. Wait for the coolant level to drop once the engine has reached normal operating temperature. Keep adding coolant until the level reaches the fill neck. Install the radiator cap and let the engine continue to run.

10

Check and fill the overflow reservoir to its prescribed level. Shut the engine off and let the engine cool. Remove the radiator cap and add more coolant, if the level has dropped. Install the radiator cap. Use the floor jack to raise the vehicle, and remove all jack stands.