How To - 2.0 Thermostat and Coolant Flush

 This "how to" assumes you have some basic tools, and safety gear. Safety glasses should be worn at all times when working with tools and automotive fluids. Always use a hydraulic jack and safety stands when lifting or getting under a vehicle. If you are unsure on where to safety lift your vehicle, refer to its owners guide. Hot boiling coolant will cause severe burns, and coolant is toxic when ingested.   The writer of this how to assumes zero liability in how to use this guide, or any damages that may come from it to you, your property, or others and others property. If you are uncertain at any point, refer to a qualified automotive technician.  Dispose of all waste materials based on your local laws.  AT NO TIME SHOULD A HOT PRESSURIZED COOLING SYSTEM BE OPENED!

Why do this:

Well, either your coolant, is weak, mixed wrong, old, or perhaps its part of another job (say a water pump).

As time progresses, coolant can be come acidic - which means that it will start to act like a simple battery.  Coolant can act as the electrolyte, and the cast iron block, and say the aluminum cylinder head are two different metals.  Over time, with this acid, the cast iron block will "trade" some spare electrons with the aluminum cylinder head.  This transfer will cause the metals to become pitted, and cause cooling hoses, radiators and heater cores to fail over time.  Coolant also acts as the lubricant for the water pump and its bearings, and seals.  Cars with well maintained cooling systems run longer and cooler without major system failures.

The coolant bottle and cap help maintain pressure on this system, keeping it sealed from pressure loss.  As pressure is raised on the cooling system, this lowers the boiling point of the coolant.  The cap has a safety valve built in that keeps the system under pressure, until a max pressure is reached, it will then vent excess pressure.  Excess pressure can rupture hoses, the heater core, and the radiator.  The coolant bottle is also the "service" point for the system.


VW uses three types of coolants in its vehicles, based on when it was produced.  G11 (blue) was used from about 1990 to mid 1996.  G11 is a phosphate free anti-freeze and is blue in color.  G12 was used from mid 1996 to 2005 - its pink in color, its also phosphate free and should not be mixed with other coolants.  G12+ is purple in color, and well, I don't know that much about it.  A lot of early to mid 90's European vehicles use G11 coolant (Saab, Mercedes, Volvo, Etc..).  Rumor has it that VW switched to G11 for the Vanagon (head gasket issue) and then pushed the G11 line into all of their vehicles to cover the costs of the Vanagon G11 supply.  Before G11 there was "green coolant" that VW  used, ( I think it was G10, but I could be wrong, it was still phosphate free..).  As a side note, GM's "Dexcool" and its family of coolants share the same basic Organic Acid Technology (OAT) as G12, at least this has been my findings from reading the Material Safety Data Sheets (MSDS) more or less the "ingredients" list.

If you want to switch coolant types, you can.  Well, that is a source of debate that I have read about for 15 years now. Basically if you fully flush a system, with lots of water, and do this a few times to remove all the traces of the coolant, you can switch from G11 to say G12, or from G12 to "green" coolant.  There is also talk of the G11 coolant was changed to G12 due to yet another head gasket issue with the VR6 engine, and by this time the Vanagon had been phased out in 1991.

Coolants, regardless of type, should be mixed with 50% water and 50% coolant.  Meaning, a 1 gal bottle of coolant will really make two when mixed with water.

Its very import to remember - never mix coolants, avoid "universal" coolants.  Also use DISTILLED water to mix any coolants!  The metals, chlorine, iron, calcium, and scale in household tap water will only weaken the coolants abilities to fight acid.  Distilled water can be found at most drug stores and food stores for $1.00 a gallon, a low cost for a job that you may only do a few times on a vehicle as you own it.

If coolant has been mixed, or is brown, or - well you don't know what the hell it is - flush out the system with water.  Avoid and type of "system cleaners".  These just cause problems.  Don't even think of asking for G11, or G12 or G12+ at a place that does not deal often with European cars.  They will just stare at you and point to towards the rack of domestic green coolants and say "this works good for me".  Buy it at the dealer, or from a place like

Thermostat failure.

The thermostat is a spring loaded coolant "blockage" that is designed to open once the engine reaches its operating temperature (about 190 Deg F).  The thermostat in the 2.0 is located below the power steering pump.  The t-stat has a small wax pellet inside of it, when the wax gets hot, it expands pushing the spring open - and allowing coolant to flow from the water pump to the radiator.  The t-stat will open and close partway while driving to keep the engine at full operating temperature.  

Signs of a failed (closed) t-stat are overheating.  Signs of a stuck open t-stat is a car that will not warm up, or when it does warm up, a high speed drive on the highway will cause the temperature to drop (below 160 deg F).  Heater output will also suffer.  Prolonged driving with a colder than normal running engine will lead to engine sludge, and a lower than normal MPG.

Its been common for many who are not familiar with VWs to think that the coolant flange on the side of the head is where the thermostat goes.  Putting the thermostat near the water pump has been a long-standing VW idea.  Since it a little of a pain to get to it, its a good idea to use QUALITY parts.

A note about the "goofy" hose clamps.

A lot of people dislike the spring loaded hoses clamps that VW (And other OEMs) use since they can be tricky and can snap your fingers.  The advantage of these clamps is that they cannot be over tightened and damage the hose, they also expand and contract along with the hoses to keep a more uniform seal around the hose.  If you find them hard to work with, spray a small amount of silicone spray around the neck of the hose to help you slip the clamps on and off without damage.  Also, the best way, hands down is to use the "right tool for the job" rather than pliers.

Tools needed

Pliers, Optional - But Recommended - Spring Clamp Pliers (shown to the right)
Metric sockets (8, 10, 13, and 14mm)
Wrenches (Same sizes)
3/8" ratchets and extensions
Razor blade
Torque wrench (ft and inch lb versions)
"Hose Pick Tool"
Assorted quality screwdrivers
Flat pan that can hold about 4 gallons of fluid
Safety Glasses
Jack stand
Floor jack

Parts needed

Two gallons of coolant, two gallons of distilled water.  
Thermostat, and gaskets
Needed Hoses and clamps
Coolant Bottle, and Cap.
Silicone spray (optional)
New belts (optional, since they come off for this job)

Step 1 - Get Parts and Tools together;

Here we see the basics of what you'll need, a Bentley manual, some distilled H2O, And G11 coolant (The tall skinny bottle is G11 from, I also got all my parts from them).

Step 2 - Once the car is cooled down, remove the cooling system cap.

This is what the coolant bottle looks like once it gets old, and has had whatever coolants mixed into it.  I could not see  how much coolant is in it since it has a brown film of scum on the inside of it.  You can't take it apart and clean it.

When I got the car, the coolant was brown.  You can see some sludge on the inside.  I had done several changes to get to down to the "clean green" color.  I needed some new hoses, and a T-stat so I felt this was a good point to change out the coolant tank, and refill the system with the OEM coolant.

Step 3 - Get under the car

On the passenger side of the car is where you'll be spending all of your time.

Remove the splashguard, its held in place to the body by two small friction clips, and then a 3rd "clip" that goes into the sub frame.  Just yank it down, it should come out easy.

I prefer to do this with the power steering (PS) system intact.  There is no need to pull the hoses or drop a drip of fluid.  I just gently hang the PS pump and lines out of the way.

Step 4 - Remove belts

For now, leave the P/S W/P belt on the vehicle, and remove the main serpentine belt. 

Slip a 13 mm long handle wrench on the end of the tensioner bolt and rotate it to the front of the vehicle.  This will release the tensioner spring.  Move the belt, and then slowly swing the tensioner back to its full rest position.  Use the wrench as a lever, not as a tool to "take bolts off".  I found that taking off the main belt aids into getting to ONE bolt that holds the P/S pump bracket to the block.  

Step 5 - Drop P/S pump and bracket.

The power steering design is a hold over from the older MK II 1.8 engine design.  And it sucks.  Let me say this first, its weak, and soft, and if you look at it too hard, part of it may break.  Don't go hog wild with a hammer on this thing.

First, you must loosen the adjuster that holds the pump to the bracket.  Just loosen these bolts, you don't have to remove them.  You may have to "apply some force" to the P/S pump body itself to get the bracket to become loose.  Three of the adjuster bolts are circled, refer to the illustrations below.  These are bolts, 12, 16, and 19 shown below.

Once you get the belt off, you can now remove the entire pump and bracket assy. off of the engine block.  3 bolts (arrows) hold the bracket to the block.  The two lower bolts are up behind the pump, and the 3rd is at the top.  Its sneaky, and its easy to pull out the adjuster bolt (long) rather than the shorter mounting bracket bolt.  These are bolts 11, 13, and 17 shown below.

Whatever you do, take your time, this is the hardest part of this job.  Don't just "take all the bolts out" some of the bolts hold the pump together.

Step 6 - T-Stat Housing

With the P/S pump out of the way, you can see, and get to the underside of the water pump.  There are two small 10mm bolts that hold the t-stat housing to the underside of the water pump.  If the bolts are hard to turn, - they may be bound up.  The one farthest away from the water pump has exposed threads on the backside of the housing.  Its a good idea to shoot some penetrating oil (PB Blaster) up into the backside of of the bolt and let it soak.  I broke my bolt off.

Once you get the t-stat housing down, clean it off, a LOT of coolant will come out, more will come out once you pull the T-stat.  ALL of the car's cooling system will be pretty much empty at this point.

Here we see the longer (good) bolt and the shorter (broken) bolt.

This is what happened after I tried to drill it out, and then TAP a screw extractor into it.  Busted flange.  Well, since the bolts get down to 89 In/Lbs I plan to risk it. (Ps, it holds fine)

Step 7 - Remove old hoses and install and/or/flush system

This is the main "hose" of the system, this is the older style OEM design used until 1996, when VW went with a more "leak free" hose.  A lot of these smaller hoses are no longer available, so I had to order the single unit design.  You can see where the previous owner had installed two older screw clamps in place of the OEM spring clamp fittings.  I replaced these, and it was easy since I had the spring clamp tool.

Older hose (above) and the newer style hose (below).  Since the Golf/Jetta design has some odd shaped hoses, I say do them one at a time, and don't get them mixed up or crossed.  Its easy to do with the heater hoses.  Check them for proper placement and fitting before going hog wild.

I left the T-stat out while I changed the other hoses. In-between each hose change I flushed the hose inlets and outlets with clean water, then chased the system with some distilled water, then blew about 10 PSI of compressed air into the system to force as much water out as possible.  Do NOT use more than this pressure as it could rupture radiators and heater cores.

I also swapped out the crappy water outlet flange (on the side of the head), and replaced my ECT and A/C overtemp sensors.  Get new o-rings, and apply a light film of *water* to them before you install them.  


Step 8 - Putting things back together.

The following diagrams have some torque specs.  The most critical is the spec for the T-stat housing, stripping out these bolts will lead you to installing a new water pump, or using helicoils.


Step 9 - Filling it back up.

With my new hoses, I filled the system.  I left off the top of the radiator hose (loose) while I filled the system to give the trapped air a place to escape.  Once I had seen coolant come out of the top hose, I put the hose and last clamp on.

 When filling the system - keep these general rules in mind:

Turn the heater on "full hot" - 
The cooling system cap MUST remain "OFF" while filling, at no time should the system be subjected to pressure.
Don't let the car overheat.
Make sure the cooling fans are working.  
Alternate the RPMs between 2500 and idle about every 30 seconds to force the air out of the system.

This process can take up to 20 min.. 

The heater should get hot.  If the car is overheating, and the heater is COLD there is AIR trapped in the system.  Turn the car off and let it cool down.  Massage the upper hose.  It should get hot.  Once the car cools back down, start it again and keep filling.  Some 2.0s seem to catch a lot of air.  This is somewhat normal, and may take several cycles with a full empty system.

If the car is overheating, and the cooling fans are NOT working.  Check to see that the thermo-switch in the radiator is hot.  If its cold, the fans will never turn on, and the system has air trapped in it.  If the switch is hot, make sure coolant has not dripped into the fan control unit (under the coolant bottle).  A really dumb place for a piece of electrical equipment.  Another trick is to turn on your A/C.  This should also turn on the cooling fan.

Added Note - May 30th 2006 - From Vortex User HK1980

"ok start the car up after its cooled down, with the reservoir open, add coolant/distilled water slowly, with the heater on full blast, just let it idle for a few minutes, then start reving it up to 2000-3000 a few times, and then start massaging the upper hose, when you massage it you are creating different pressure passage ways, so you'll see the air trying to escape on its out route, you'll see the bubbles form at the top of the reservoir ,a trick is to pinch the top hose rev it up for a little, and then let it go, pinch the hose and let it go, you'll see HUGE bubbles start to come out from the reservoir top, keep doing this until you feel the bottom thermostat hose is hot, and make sure your heater is blowing hot air, and the car is not overheating, if this cycle doesn't work the first time around, cap the system off, go drive it around the block a few times with the heater on still, then park it and let it kool down, and do the process over, it may take up to 3-5 times of doing this to get it done, if you get really good with pinching the hose and making the passages for the air bubbles, you can do it in 2 tries.  Once the lower thermostat hose is getting hot, make sure the fan switch is hot also, and once the fans do come on, cap it off, and let it cycle for a bit.....

I know Dan and the others dyi's say never cap/pressurize the system, but if you are doing this over and over,
one thing is, if its overheating just don't turn the car off with the reservoir still open, cap the system and let it kool down, if its starts to overflow its going to let more air in, and you'll be going in circles, at least force the coolant back into the coolant system, and not out of the reservoir, then let it cool down for awhile and do it over

I also have a Neuspeed upper strut stress bar.  I did NOT have to remove it in order to change out the coolant bottle.  Using a stubby 10mm wrench I was able to work out its mounting bolts.

I also have (shown) a slightly overfilled cooling system.  This is since the pressure is low, and the system was just filled.  I add this amount so that once ALL the air is out of the system, and the system is under pressure, it will be at its "MAX" mark.

Once the system has been run, and its running at normal temperature, and the water level is not drastically changing in the coolant bottle.  Cap the system and go for a test drive.  Keep an eye on the coolant gauge, and the heater output.

And Remember: