This DIY was written by Daris,
screen name DarisD on VwVortex. Do
not repost these instructions without first asking his permission.
Im sure I speak for EVERY VR6 owner when I say - Thanks Daris!!
Honorable mention to the Dr - VgRt6 (Gary) for help working out the minutiae of this
DIY describes how to replace the thermostat housing and coolant distribution
pipe (AKA crack pipe) on the MKIV AFP VR6 motor (very similar procedure for AAA
VR6 engines). This covers most of the weak spots in the coolant distribution
system. If you have a leak in one spot, consider replacing as much as you can
afford. At the very least, replace all o-rings and the thermostat. Next most
important, replace the sensors, housing, and pipe. If you have not done so
already, you might as well replace the water pump. Check hoses for condition and
replace as necessary. If you do not replace the plastic parts, at least check
them very carefully for stress cracks and repair with JB Weld or other
high-density epoxy product as necessary.
The chrome, billet crack pipe installed in this DIY can be ordered from www.GruvenParts.com in either chrome or polished finish. You will truley never have to reference these instructions again!!
from www.GruvenParts.com -- You should
consider replacing ALL spring type hose clamps with screw type clamps.
You will find the spring clamps very difficult to get at to remove.
Its easy to make a mistake and not seat the spring clamps fully as well,
resulting in leaks. The screw type
clamps are very easy to install, using a 5 or 6 mm socket on a swivel head.
Just a hint! - Paul
Spark Plug Wire Puller
5mm Hex socket or similar. It should be short (no long t-shaped wrenches)
10 and 13 mm sockets
Various socket extensions
Flathead screwdrivers (thin and wide)
Phillips head screwdriver
Channel-locks or similar wrench for hose clips (short handles good)
Thermostat Housing Seal
ECU Temp sensor
2 sensor O-Rings
Crack Pipe (www.GruvenParts.com billet pipe, or stock) [if you feel like doing all this again in a few more years – Paul, www.GruvenParts.com]
Screw-style hose clamps (5 at 2 inch max dia, 1 at 1 inch max dia)
Alot of paper towels
RTV Silicone Sealant (optional)
Threadlocker or Anti-Sieze (optional)
Get the lock carrier assembly to the service position using this DIY:
Lock Carrier to Service Position
Precautions and Obvious Stuff:
Wear gloves and skin covering clothing at all times, and consider eye protection. Change your clothing if it becomes soaked in coolant. Coolant can soak through skin if left for long enough. G12 is extremely poisonous stuff. It contains Ethylene Glycol, Diethylene Glycol, and Sodium Hydroxide, just to name the most dangerous ingredients. It has a sweet taste and smell, and is attractive to children and animals for this reason. Even a small amount can cause irreversible damage to your liver and kidneys. Ethylene Glycol in the bloodstream catalyzes into several harmful intermediaries, mostly acids, ending in things like Oxalic Acid that can lead to crystals in your urine. The early stages of poisoning feel similar to ethyl alcohol intoxication. I strongly recommend you abstain from alcohol consumption while working with coolant for this reason. If you even suspect that you have been poisoned: take a shower, get yourself out of the garage, and call your doctor. Early intervention could save your life and has a high success rate. Death from glycol poisoning is SLOW and PAINFUL. You have been warned!
Part 1: Getting Things Off
Remove the airbox. This will give you access to the back of the thermostat
housing. The airbox is attached with two 10-mm screws and is held in place with
a rubber damper. When you are done you can now see a small sliver of the
thermostat housing, as in this picture:
Remove the top engine cover (the thing with the chrome Vr6 emblem). This gives
you easier access to the coolant and smog pump lines just beneath the coil. To
do this first pull the spark plug wires using the tool and pull them from their
channels, then remove the six or so T25 Torx screws. Then remove the oil filler
cap and pull the cover, and replace the oil filler cap. I would also put the
screws for the cover back in their holes just to keep track of them.
it is time to get some hoses out of the way. Here is the view you should see
from the front of the vehicle. This image has been colorized. Yellow is the smog
pump feed hose, and red is the upper-coolant-manifold-spaghetti thingy.
Get the smog pump supply line out. This is the plastic corrugated hose that has
the rubber protectors on it that seems to be snaking around the outside of this
morass. You may have to cut a zip tie. Squeeze the connectors on the fatter
textured sides and pull straight back to get them off. The connectors may stick,
keep in mind that they are sealed with o-rings so see if a little twist sets
Now focus on getting the y-shaped coolant hose manifold thingy on the front part
of the thermostat housing out. You already have the coolant hose coming out of
the top of the radiator off it. Now remove all the other connections that the
hoses coming from this manifold-assemblage have. The connections are: throttle
body (connects to a steel rail next to the coil pack), aux radiator (connects to
a steel rail in front of the intake manifold) and thermostat housing. The hose
that attaches just to the right of the sensors on the thermostat housing will be
EXTREMELY tight work, be prepared to curse but rest assured that someone got it
there and you can get it off if you keep at it. This is what it looks like when
it is free.
Now remove the lower thermostat housing hose. This one is particularly difficult
to get at as well. See the yellow arrow in this image:
Carefully unclip the electrical conduit attached to the bracket on the outside
of the thermostat housing. See the image above, the red arrows. Two are shown,
there are three total.
we will move to the back part of the housing.
Remove the hose going to the afterrun-pump which angles sharply off the back
side of the thermostat housing. See the image above of the area behind the
airbox for an idea of the hose I speak of. Of all the hoses, this is the hardest
to get off. I had to remove both sides, starting with the side closest to the
pump first so that I could bend the hose far enough to get my channel-locks in
to the other clamp. The extreme angle of the hose where it attaches to the
thermostat housing will make getting the clamp out of the way challenging.
Whatever you do, be careful not to mar or cut the hose. Hoses get $$$$ fast.
you have everything out of the way to get the thermostat housing out.
Remove the three bolts holding the housing to the aluminum head. There are two
long bolts that are on the front-top, and one small one tucked behind the
housing. Here is a picture of the longer screws and the bracket. Pay close
attention to the orientation of the bracket, you will want to put this on the
is a picture of where this smaller one is located. Be sure you have the right
bolt, as the other two pictured are for the timing chain cover.
Remove the thermostat housing. First break the seal free and then work it out
through the front of the vehicle. Set it aside for the next section so we can
check sensor condition etc.
we need to get the coolant distribution (crack) pipe out. Take a look at the
situation. At this point you probably cannot even see the pipe, except the
business end that slides into the thermostat housing. The main thing in your way
is the smog pump, but there are also sensor connectors, wires, air hoses, all
sorts of things in your way.
we will remove the smog pump. This is very tricky. Note that the pump is
connected to a plastic bracket that snaps onto a robust metal bracket that
shares screws for the intake manifold. This configuration makes it easy to
assemble but difficult to remove. Refer to these pictures and take a minute to
feel around for the three bolts you will need to remove first.
(plastic bracket in yellow, metal bracket in red):
Unplug the Smog Pump. This is a large plug close to the end of the crack pipe.
See the "before" picture, red arrows. Also unclip the relay that is
clipped to the pump bracket near the bottom.
Disconnect and remove the smog pump send hose. This is a high pressure hose and
will be a little more difficult to remove than the intake side, but is not
Remove the screws attaching the pump to the plastic bracket (5 mm hex). The
front two are not a problem. The back one is more difficult. You will either
need a long extension for a socket, or some very creative work. Try a hex socket
on a long extension. The hardest part here is getting the socket into the bolt.
Now get the pump out of there, going between the alternator and the large AC
hose. It is a tight fit but believe me it comes out eventually. If it seems like
you are breaking things, continue to step 14 and see if you can get the bracket
Now get the bracket off. This is necessary to get the oil cooler send hose off
the crack pipe. Look carefully at the "after" picture above. Get a
wide but sharp screwdriver and insert it under the plastic retaining clip (two
yellow arrows in picture), and give it a little twist, pulling and rocking the
bracket back and forth. Both parts are quite tough, so do not feel like you have
to baby them.
SMOG PUMP REMOVAL PROCEDURE: If you have done this before, and
you were conscientious to lubricate and clean the clip well, it should be
possible to unclip the entire assembly from the metal bracket. This is trickier
but could save you ten or so minutes.
we will remove the crack pipe. Here is a picture of the pipe on my car, with a
shiny new pipe to show the orientation. This chromed billet pipe is made by A2T2
(Paul) and you can buy it direct from him at www.GruvenParts.com.
If you have a camera, take a quick picture of where the wires and brackets are
located, as yours may be different. As we will see, the tolerances between parts
and systems here are measured in millimeters.
Drain the crack pipe. This one is messy. The drain has to be accessed from
underneath the car, and is just next to the block where the water pump housing
fits. The stock pipe will need a flathead screwdriver and a turn or two, then it
pops off. WEAR EYE PROTECTION!!!
Take the oil cooler water send hose off the pipe. This one is tricky but at
least you can see it easily. More coolant will spill. I swear, we are almost
Free the plastic cable/plug bracket to the right of the oil cooler hose nipple.
The two connectors come out easily, and the wire harness clip on the bottom just
needs to be snapped open. Be careful as this is not the most beefy part. Pop it
off the bosses and set it aside.
Pull the crack pipe from the car. More coolant will spill.
are done. Take a break, change your clothes, etc.
Part 2: Reassembly
Fit the crack pipe to the block. Expert tip: it is hard to get your eye in
there, but check the hole where the pipe fits into the block for corrosion or
scale, and remove with 400-grit sandpaper if you find any. If you are re-using
the old unit remember to replace the o-rings. If you are using the billet crack
pipe from www.GruvenParts.com, verify that the hose clamp for the
block-coolant-exit-hose (just behind where the pipe goes, to the left of where
the nipple is on the pipe) is completely below the the 9-oclock and 3-oclock
positions to avoid contact with the pipe, which would cause this hose to be cut
by the clamp and possibly the crack pipe to not even fit correctly. Refer to
this picture -
a small amount of lubricant, coolant or grease, on both rubber o-rings of the
pipe. Alternately, you could use RTV on one side at a time (block side for this
step) and work it in wet. Slide it into place in the block, twisting it slightly
to keep the o-ring from being cut or bound. It should slide in like a hot
knife in butter. If not, verify that you have the right alignment, check for
obstructions, check for scale inside the throat, and try again. Just remember to
be patient as the o-rings are the only thing holding the water in.
Get the thermostat housing ready for installation. Replace the o-rings on your
two sensors. Be VERY careful with these, do not twist them off or on, just
pull straight back. Daris twisted his and the bases cracked free of the
housings, forcing him to replace them. PAY ATTENTION TO ORIENTATION WHEN YOU
INSTALL THESE! See the image or compare to the orientation of the sensor plugs
in the harness to see what side should be where. The three tabbed sides of the
two plugs SHOULD be at the 1, 9, and 6-oclock positions. See the white arrow in
the image below. Again, NO TWISTING ALLOWED! The larger of the two (temp sensor)
is fairly expensive so be careful. Remember to replace the thermostat (it is
inside the housing). Expert advice: use a tiny bead of RTV to seal the
thermostat in. Finally, put the wiring loom clip on with the two longer bolts
(align as with the yellow arrows below). You should have something that looks
check the mating surface with the head. There could be a fair amount of crud
here. If this is very dirty and it does not come off with a rag and elbow
grease, carefully clean the surface. Use a small flathead screwdriver CAREFULLY
for the hard crusty stuff, like a dentist would pick plaque off your teeth.
Finish with a dremel with the conic bronze wire polishing tool to finish the
surface. Remember, this is aluminum. Expert tip: if there is any deep galling or
pitting, patch with JB Weld and sand it flat with 400 grit paper.
Install the thermostat housing. First get some grease and put it in the channel
for the rubber o-ring that seals. Not too much (See the science note above for
why). Fit the rubber o-ring in. Be observant: IT SHOULD NOT WANT TO POP OUT OF
THE CHANNEL! If it has a tendency to do this, try more grease. If it does not
stay in place even then, consider the possibility that you have the wrong or a
bad gasket. The important thing is that this o-ring should stay put while you
fiddle with the three bolts getting it in place. Now get the two long bolts and
the wire harness bracket on. If you want, put some blue threadlocker or anti-sieze
on these. Working from the front of the car, wiggle the housing in between the
battery, hoses, and conduits. Once in place, veryify that the seal is still in
the channel by peeking in with a flashlight. Now start the two long bolts. Just
START them. Now we need to start the back bolt. Again, blue threadlocker if you
have it. It is difficult to get this one started, but be patient. It helps if
you do not have the other two bolts in too far. Be CAREFUL not to cross-thread
these: aluminum is softer than you think. Also, check that there is no binding
with the crack pipe, and that this can still rotate inside its two cups easily,
and before continuing make sure that the nipple on the crack pipe comes out
straight and level.
the tedious part. Slowly work each of the three bolts one at a time into the
head. Try starting with one, screwing until the gap is about a couple
millimeters, then get them all going a turn at a time. This is important to
ensure that the gasket does not bubble out, which would force you to tear down
and start over if it caused a leak, or worse fail on you later. TAKE YOUR TIME.
Final torque is 10N-m/7ft-lbs.
Clip the wire loom into the thermostat-housing clips. There should be three
clips (see the yellow arrows in the image above).
Replace the hoses accessed from the area where the airbox goes. Replace the hose
going between the thermostat housing and the afterrun pump, back by the shifter
mechanism. Now replace the hose coming from the bottom of the radiator, which
fits onto the housing pipe below the thermostat. We strongly recommend using
screw-style clamps for these three, to facilitate future replacements, and face
the screw ends towards the airbox.
Replace the air filter housing. Remember to reattach the smog pump air supply
hose. You are now done with the back section.
Finish the crack pipe installation. See the image above. Note that the part
marked with the red arrow is from what I could tell completely useless, I threw
it away. Fit the crack pipe harness clip over the crack pipe (white and yellow
arrows). Note that the billet pipe from www.GruvenParts.com
does not have the bosses for this clip (white arrows) but they do not really do
much except keep the harness clip from rotating (you can easily just use zip
ties if you want). Clip the two sensor plugs into this (thin yellow arrows), and
clip the wire conduit below it inside the trap on the bottom (fat yellow
arrows). Replace the oil cooler coolant supply hose onto the nipple (blue
arrows). Do NOT use a screw style clamp here: there is not enough clearance
between this hose and the smog pump bracket for you to place the screw on top of
the nipple, and any other orientation is more of a pain to access than it is
worth. The clip ends should be just below the 9-oclock position. More
specifically, the clip ends have to be completely below horizontal or the smog
pump bracket will not fit at all.
Attach the hoses to the front of the thermostat housing, aux radiator rail, and
throttle body supply attachment points. Use screw-style clamps for the
attachment to the thermostat housing and aux rad supply, the smaller feed for
the throttle body does not require a screw style clamp. The point here is making
access to these hose clamps easy without requiring removal of the lock carrier,
which as you have seen is a pain. Point the mechanisms of these two new screw
Attach the smog pump. Clean and apply a little oil or grease on the metal
retainer that the plastic bracket attaches to, this facilitates installation.
Attach the smog pump to the bracket. Now, working slowly, move the pump in
through the space between the alternator and the AC hose. Once in place, jam the
plastic bracket over the metal retainer. If you have difficulty doing this,
attach the bracket first then the smog pump, but this will be more difficult due
to the clearances and the difficult access to that back screw.
Finish the smog pump. Attach the supply and pressure hoses. Clean all
attachments and apply some grease to keep the o-rings in good shape. Plug the
You are done. Check for any loose ends, and proceed with replacing the lock
carrier assembly (See the prerequisite). Check for any leaks carefully on fill