Wife's car: 2002 Passot 4motion; auto; 150K; purchased new. Leak is not oil, trans fluid, power steering fluid, or wiper fluid; this is verified by the coolant level in the reservoir going down. Two doses of stop leak has slowed it way down but it still leaks somewhere. There are some finger size holes in the bottom of the bell hosing. There is also a slit in the bell housing and the ring gear is fully in view. The anti freeze is coming out of one of the finger size holes and blows across bottom of trans and cat and stains them. Ring gear looks fine. I took the engine covers off to look at the pipes at the back end of the motor (up against fire wall). To do this I removed some of the 9,000 vacuum lines back there to get a better look. Of course 10 year old, brittle lines do not like to move and consequently disintegrated. I had a good view back there but not perfect. I could get an inspection mirror in there and I could feel around the rear water pipes and hoses to the heater with my hand. This inspection showed no leaks or any signs of anti freeze discoloration in back of engine. I have car on a lift so the view from underneath is as good as one can get. Nothing is seen except for antifreeze coming out those holes. I had a water boxer van with lots of leaks so I do not want the same problems with Passot. I would like to find the leak and fix it properly.
Having found nothing, I put car back together and come up with these questions:
1. Do these engines have a reputation for coolant leaks like the water boxer?
2. Where do the trans cooler line go in the trans? Is it possible this is the source of coolant dripping from bell housing?
3. If, indeed, the water pipes at the back of the engine or the heater supply pipe needs replacement, must the engine be pulled?
4. Could there be a bad thermostat or a bad head gasket that is causing system to over pressurize; thus forcing coolant out the over flow vent from the overflow tank? (This was an early water boxer problem.) The vent is at the rear of the tank and sits over the left side (driver side) of the bell-housing.
Check under the intake manifold. There are metal water pipes running underneath there that use o-rings as a seal. Over time, the o-rings will wear out and start to leak. This was the source of the leak on my B5. The o-ring is $1, but the process takes a few hours to do (drain coolant, remove intake, replace orings, reverse process).
You should be able to see it with just a flashlight before removing the manifold. There will either be a small puddle, or dried up pink stuff. If that is indeed the source of the leak, I would recommend you replace all the orings down there while you have it all pulled out. Also it's recommended you replace the intake gasket.
Just something to be careful of, the EGR hose over time also gets very brittle. You will have to remove this to do this fix and it could break during removal or re-installation.
When I look with the flash light, am I looking at the back of the engine (next to fire wall)? I have already looked; negative result. As I said in original post every thing looked fine except for a little dirt and dust. I know about vacuum hoses. Must be made out of same stuff as Mercedes wire harness. About five years ago the heat exchanger was replaced under the dash. This is a suspect. I need to do a pressure test. Will advise when accomplished. First have to fix an EVAP problem on a 2000 cabrio so it can pass inspection before the end of August.
I chaste my leek down , it was behind the engines fire wall where the cabin filter , battery and brake fluid are kept , Take the large cover off to access that area , in there you will see between the battery and brake fluid reservoir is a splash guard covering over the heater hose and heater core connection . Pull that cover off the hoses , it's tuff , look and see if you see any dryed antifreeze , my heater box was leaking there , a hair line crack on the heater box pipe and the antifreeze was going down the drain that is wright below the hose connection , also you have to have your antifreeze reservoir full to check for the leek , it is the high spot in the cooling system above the reservoir , if coolent is low it has air there by the heater core and no leek will be visible , now start car turn on the heater Max and check for leeks , if it's the heater core this is how to change it out. USE ONLY VW ANTIFREEZE G12
Lots of times the plastic housing on that the coolant temp sensor mounts in on the back passenger side of the engine cracks. This causes coolant to drip down the backside of the engine and down to underneath the car. Look at the plastic housing where the sensor is and if there is any pinkish crusty residue, then that is your problem.