Service Bulletin: VW Jetta Coolant System for 1.9L 8 Valve Engine

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The cooling system is one of the most important areas to pay attention to during VW Jetta timing belt replacement. To ensure that your new VW Jetta timing belt components and water pump last until the next 75,000 mile change interval, it's important to re-create the engine's condition as it was when it left the factory. You can not be lazy when it comes to the water pump and timing belt replacement! Cutting corners now adds time, labor, and money later.


VW Jetta timing belt installation is a complex repair procedure and should be performed by experienced automotive technicians, trained in performing proper timing belt installation.

Blauparts recommends that an Audi VW Factory Trained ASE Certified Technician perform timing belt repair on your VW Jetta. Someone who has been trained in timing belt procedures for your exact vehicle model. This is for your safety and to prevent improper installation by untrained and unqualified installers and technicians, which may lead to possible engine damage.

Always read the factory service manual safety instructions and guidelines.


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How to prevent premature VW Jetta timing belt component and water pump failure?

It is the installer's responsibility to take the necessary time to follow the steps outlined in this bulletin to prevent future labor costs, as well as, any inconvenience after the installation of the water pump during timing belt replacement.

Flushing VW Jetta Coolant

It has been noted that due to time constraints, inconvenience, and profit, many individuals, mechanics, and repair shops, do not take the extra time needed to thoroughly flush the entire cooling system prior to the installation of a new VW Jetta water pump and related timing belt components.

It is imperative that the cooling system be thoroughly flushed of all accumulated silt and sediment build up, including all aftermarket cooling system additives, or stop leak products that may have been added to the cooling system, past or present.

Just draining the cooling system and refilling it is not enough! Thoroughly flushing the coolant involves flushing the radiator, engine block, heater core, and hoses entirely.

DO NOT USE Cooling System Flush Products since many contain muriatic and/or other acids. Remnants of such acids left in the cooling system can cause your new water pump to prematurely fail.

Premature water pump failure (bearings and seals) can occur if you don't take the time to flush the entire cooling system and it's related components. Often when problems arise, such as a coolant leak, the new water pump is blamed as the cause when if fact the opposite is true. It's usually because the installer has neglected to follow this important step.

Example 1) VW Coolant Contamination Caused By Old Age

VW Jetta Coolant Flush

Blauparts purchased a used 1-owner 1997 Audi A4 with every service record from the date of sale. The vehicle had regular oil changes, preventative maintenance, and was in really good shape. Despite the great service history, note the G12 coolant sediment and contamination that was removed when we drained and thoroughly flushed the system. Even when using approved coolant, years of continuous circulating through the engine causes a measure of sediment to buildup. Similar to motor oil, over time coolant (even long-life) becomes weak, is depleted of it's additives, breaks down, and "gets dirty" causing this pictured sediment. It's important to thouroughly flush and remove all of this sediment during timing belt replacement. Re-creating the engine's condition as it was when it left the factory will ensure that your new components last until the next 75,000 mile change interval.

Example 2) VW Coolant Contamination Caused By Coolant Flush Products

Normal worn VW water pump.Premature VW water pump failure due to bad coolant flush.

Image 1) Original water pump removed from a Audi A6 2.7T with approximately 80,000 miles. This pump was not leaking. Note the normal discoloration of the aluminum casting. This is the result of minimum coolant contamination for this type of mileage.

Image 2) Water pump removed from a Audi A6 2.7T with less than 3,000 miles due to leaking. It was wrongly assumed that it was a manufacturer defect. However, the evidence revealed that the leak was caused by coolant contamination. Note the abnormal black discoloration of the aluminum casting. The cause was a result of an additive (likely a flushing agent) containing muriatic acid/other acids being used (before or after the water pump replacement). Acids left in the coolant system ate away at the internal seals and caused premature water pump failure.

Proper VW Water Pump Installation

The key to a factory quality seal is in the preparation of the surface area. Take the extra time to properly clean the VW water pump gasket and thermostat o-ring surfaces thoroughly. These surfaces should be free of all old gasket material and corrosion build up before installing your new VW water pump and thermostat.To achieve the optimal just like new surface, it's usually necessary to use a medium grit scotch brite pad and/or angle die grinder with a medium grit scotch brite conditioning pad (see the video below).

When the water pump mounting surfaces are thoroughly cleaned and smooth, gasket sealing agents are not needed! Again, gasket sealing agents (Form-A-Gaskets, gel or spray forms) should NOT be used with the paper water pump gasket. Sealing agents vary in composition and intended usage, and when used in conjunction with paper gasket's may affect the paper gaskets long term ability to compress and/or perform its sealing function. Appropriate gel like gasket sealing agents should only be used in the case of severe pitting of the engine block surface in the event an even and smooth mounting surface for the water pump is not attainable.

Some installers have used sealing compounds which can significantly reduce the sealing function of the VW water pump gasket. It is important to note that no sealing compounds were used when mating the water pump to the engine block from the factory. The factory Robert Bentley manual makes no reference to using sealing compounds during water pump replacement. Besides not being recommended or required, sloppily applied sealing agents can contribute to cooling system contamination. It is important to pay attention to and follow the manufacturer's installation instructions. Sealing agents (RTV Form-a-Gasket silicones, aerosol adhesives, or sealants) should NOT be used!

Double check all water pump mounting bolts for tightness. A loose or missing water pump or thermostat housing bolt can result in a leak and falsely attribute the water pump as defective.

How To Properly Prepare The VW Water Pump Gasket Mating Surface Video

Filling VW Jetta Coolant

Read the warnings on the antifreeze coolant bottle.
Improper use can be harmful or fatal.

Use only approved Audi VW G12 antifreeze coolant. Most G12 coolant sold on the market is concentrated. You must dilute the coolant. Mix 50% coolant with 50% deionized water. Deionized water is preferred. However, if it is not available you can use distilled water. Do not mix tap water with new coolant! Tap water varies in chemicals, minerals, ions, and Ph levels. These factors can adversely effect the new coolant, a new water pump, and other cooling components.

Mixing and Maintaining VW Jetta Coolant

Mixing other brands of unauthorized coolants with the approved G12 coolant can also cause an adverse chemical reaction, causing the coolant to gel and clot. This can damage the new water pump, plug the cooling system, and weaken other plastic cooling system components, such as the radiator and plastic coolant hose connections.

Water Pump Break in Period

Water pumps are inspected and air pressure tested at the factory for any leaks. Per the manufacturer, all new water pumps have a break in period. Shortly after startup, it is not uncommon for a new water pump to have slight seepage or coolant discharge coming from this hole below the water pump pulley. This is because the unique seal material in a new water pump is designed to 'bed in' as the impeller shaft spins. Slight weeping or dampness from/or around the discharge 'weep plug' or cap is allowable for at least 100 miles after installation and should not be attributed to a defective water pump.

In extreme cold climates (below freezing), it's important that the correct coolant mixture ratios be maintained. If the coolant ratio is incorrect, it can cause weakening of the machined weep hole tolerances causing a leak.


Be environmentally responsible. Dispose of the old anti freeze coolant properly.


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