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Pelican Technical Article:

Coolant Flush and Replacement

Jared Fenton


1 hour1 hr


$20 to $140




Vacuum bleeder, large drain pan

Applicable Models:

VW Jetta GL (1999-05)
VW Jetta GLS (1999-05)
VW Jetta Wolfsburg (1999)

Parts Required:


Hot Tip:

Be sure to have a drain pan of at least two gallon capacity

Performance Gain:

Prevents overheating and corrosion

Complementary Modification:

Replace coolant expansion tank

One often neglected task on many cars is the maintenance of the cooling system. In general, I recommend that you flush and clean out your cooling system every two years. The reason for this is that old, exhausted coolant can actually cause irreversible damage to your engine components. Over time, the old coolant can become corrosive to aluminum and cast iron.

A properly maintained cooling system must have a few things in order: adequate supply of coolant, a radiator that acts as a heat exchanger with the outside air, a fan or air flow source, a water pump to keep the coolant circulating, and a thermostat to regulate the engine at its optimum operating temperature. The coolant must also have the correct mixture and chemical compounds to promote heat transfer, protect against freezing, and also inhibit corrosion. To keep your VW operating correctly, it's important to check the level and overall condition of the coolant on a regular basis. You also need to change the coolant before it degrades to the point where it doesn't perform its job adequately. It is also important that you use the G12 coolant specified by VW. This coolant has additives that are specifically designed for the engine to prevent corrosion.

It's very important to check your coolant level regularly, as this will help detect leaks that can siphon off coolant and cause overheating in your engine. You should regularly check the coolant level in your coolant reservoir, making sure that it is within the prescribed High/Low marks. These marks are printed on the side of the coolant container. The container is slightly transparent. You can see through it slightly to see the current coolant level.

Your car will lose a little bit of coolant here and there over time due to evaporation from the reservoir. However, a significant loss of coolant over a very short period of time almost certainly signifies a leak in the system. Sometimes a leak can be seen when you park the car overnight. Often, the coolant leaks out and then evaporates while you're driving, leaving no tell-tale mark of coolant on the pavement. If you suspect a coolant leak, visually inspect all of the hoses, the water pump, the reservoir, and the radiator for seepage or the 'weeping' of coolant out of seams and gaskets. If you suspect a leak that you cannot see, a pressure test from a professional mechanic can verify the integrity of your system.

In the case of the Mk4 2.0, you'll need roughly one gallon of coolant along with one gallon of distilled water.

With your VW cold, jack the car up and place it on jack stands. See our article on Jacking up Your Jetta for more information.

You'll want to have a drain pan of at least three gallons capacity to catch all the old coolant. Crawl underneath the car and find the radiator drain plug at the bottom right corner. Pull the valve out and rotate it counterclockwise. Let the old coolant drain completely. Once empty, close the valve.

When filling the system, I recommend using a vacuum bleeder to remove all the air from the system. These work like a siphon, sucking all the air out and creating a vacuum in the system. Don't be alarmed if you see the hoses collapse. This is normal.

I've found that bleeding the system the old fashioned way with modern cars really doesn't do an effective job of removing air pockets from the cooling system.

The advantage of this type of bleeding is that it can also determine if there's a leak in the system. If there is, the system won't hold a vacuum. Once you have determined there are no leaks, use the transfer hose supplied with the bleeder kit to suck the coolant into the engine. If you have done it right, you should be just at the correct level when the system pressure equalizes.

Locate the radiator drain valve at the lower right side of the car.
Figure 1

Locate the radiator drain valve at the lower right side of the car. You'll want to have a drain pan underneath of at least three gallons capacity. Pull the knob on the drain valve (green arrow) and rotate it counter clockwise. This opens the valve and allows the coolant to drain.

Allow the old coolant to drain completely from the radiator.
Figure 2

Allow the old coolant to drain completely from the radiator. Be sure you have a large enough drain pan. Once empty, turn the knob clockwise and push it inward. This closes the valve.

You'll need to fill the system from the coolant expansion tank.
Figure 3

You'll need to fill the system from the coolant expansion tank. Loosen and remove the cap (green arrow) and attach the vacuum bleeder.

I like to use a vacuum bleeder to evacuate the cooling system of air pockets.
Figure 4

I like to use a vacuum bleeder to evacuate the cooling system of air pockets. My favorite unit is the Airlift system, available through Pelican Parts. I highly recommend using this tool when filling the system with new coolant.

Comments and Suggestions:
Chalaz Comments: What if you add ordinary water without coolant,will it cause over heating as well?
February 19, 2017
  Followup from the Pelican Staff: The only issue with that is corrosion, and excessive wear on the water pump from lack of lubrication. It shouldn't over heat though. - Casey at Pelican Parts  

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Page last updated: Sun 2/18/2018 03:26:01 AM