Just finished replacing the coolant flange and heater core hoses on my 2001 Passat GLS, so posting the job notes. Several other posts on this topic, so I'll try to add to those. Definitely a PITA job. Looks like my hands were in a fight with 10 cats! Off to the notes then:
Recently a coolant leak started getting worse, with the fluid ending up more on the DS than the PS. Others have mentioned flange problems dripping on the PS, but that wasn't the case for me. I read the posts about the flange being the most likely culprit, so I decided to swap it out, along with the hoses. Went with the Uro Tuning cast one, which was lovely. Looking back I don't think I needed to replace the hoses - putting hose clamps on to fix the coupler leaks would have done it - but ah well.
General Prep - the usual to get started. Pulled the cowl off, disconnected the battery, drained the coolant, and got the coolant reservoir up and out of the way.
Vent Pipe Fun - the two vent pipes, the 3-way connector, and the heat shield all need to come off to make space. Be sure to remove both hoses going to the combi valve.
Combi Valve - this one wasn't too bad. You just need a short 1/4" ratchet and a stubby 5 mm hex setup of some sort, and you can get the three bolts out fairly easily. As others have noted, the gasket wants to drop down into the engine, so it needs extra attention. I spent time flushing the combi valve with a whole lot of throttle body cleaner and got a bunch of junk out, so hopefully that will help. When putting the combi valve back in I used the sewing thread trick to keep the gasket positioned, and that worked great. Pulled the thread off once the bolts were threaded on.
Flange Removal and Installation - your new best friend is a 1/4" ratchet, a standard 10 mm socket, and a long 10 mm socket. The long one is good on the PS with the outer bolt, stud bolt, and the second regular bolt. The two hex bolts holding the silver fuel line (?) definitely need to come out, and then the bracket can slide toward the firewall and off the stud bolt. Most of this is blind, and I remembered to make use of my mirror a lot. Super helpful for seeing where the bolt holes need to line up. On the DS the two bolts are easy to get to with the standard socket.
Outlet Hose - this was probably my biggest headache, and ironically it wasn't a problem. Should have just left it! Getting the coupler to disconnect took gorilla strength, but luckily with all the other stuff removed you can hug your engine and get two hands on it. No option to twist these couplers because of the alignment pins/slots. I replaced the hose with a Rein one, and after it all went back together this was the problem child, I think because the hose/coupling wasn't an exact match. I put the original hose back on and all good, except for the small fortune I spend on coolant with the stuff I can't catch. I like these couplers when they work correctly - the spring is in place, you line it up with the slots, push hard, and get that nice click when it seats.
Soapy Water - figured out that spraying the heater core hoses with soapy water makes removal and installation through those holes a breeze. Well, as much of a "breeze" as you can get on a B5.
Final Analysis - once everything was out, the main problem seemed to be the crack near the coupler on the inlet hose. I could have pried off the plastic part and put on a hose clamp, but going into it I didn't know how these hoses were designed. Also the o-ring connecting the flange to the block. That thing was soft, oversized, and flattened, so good to get a new set of o-rings in there along with the metal flange. Some photos below.
Hope this helps! I'll probably do the same swap on my 2002 wagon as a preventative step. Not a bad repair, but also not one you want to deal with in an emergency.
Graham
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Recently a coolant leak started getting worse, with the fluid ending up more on the DS than the PS. Others have mentioned flange problems dripping on the PS, but that wasn't the case for me. I read the posts about the flange being the most likely culprit, so I decided to swap it out, along with the hoses. Went with the Uro Tuning cast one, which was lovely. Looking back I don't think I needed to replace the hoses - putting hose clamps on to fix the coupler leaks would have done it - but ah well.
General Prep - the usual to get started. Pulled the cowl off, disconnected the battery, drained the coolant, and got the coolant reservoir up and out of the way.
Vent Pipe Fun - the two vent pipes, the 3-way connector, and the heat shield all need to come off to make space. Be sure to remove both hoses going to the combi valve.
Combi Valve - this one wasn't too bad. You just need a short 1/4" ratchet and a stubby 5 mm hex setup of some sort, and you can get the three bolts out fairly easily. As others have noted, the gasket wants to drop down into the engine, so it needs extra attention. I spent time flushing the combi valve with a whole lot of throttle body cleaner and got a bunch of junk out, so hopefully that will help. When putting the combi valve back in I used the sewing thread trick to keep the gasket positioned, and that worked great. Pulled the thread off once the bolts were threaded on.
Flange Removal and Installation - your new best friend is a 1/4" ratchet, a standard 10 mm socket, and a long 10 mm socket. The long one is good on the PS with the outer bolt, stud bolt, and the second regular bolt. The two hex bolts holding the silver fuel line (?) definitely need to come out, and then the bracket can slide toward the firewall and off the stud bolt. Most of this is blind, and I remembered to make use of my mirror a lot. Super helpful for seeing where the bolt holes need to line up. On the DS the two bolts are easy to get to with the standard socket.
Outlet Hose - this was probably my biggest headache, and ironically it wasn't a problem. Should have just left it! Getting the coupler to disconnect took gorilla strength, but luckily with all the other stuff removed you can hug your engine and get two hands on it. No option to twist these couplers because of the alignment pins/slots. I replaced the hose with a Rein one, and after it all went back together this was the problem child, I think because the hose/coupling wasn't an exact match. I put the original hose back on and all good, except for the small fortune I spend on coolant with the stuff I can't catch. I like these couplers when they work correctly - the spring is in place, you line it up with the slots, push hard, and get that nice click when it seats.
Soapy Water - figured out that spraying the heater core hoses with soapy water makes removal and installation through those holes a breeze. Well, as much of a "breeze" as you can get on a B5.
Final Analysis - once everything was out, the main problem seemed to be the crack near the coupler on the inlet hose. I could have pried off the plastic part and put on a hose clamp, but going into it I didn't know how these hoses were designed. Also the o-ring connecting the flange to the block. That thing was soft, oversized, and flattened, so good to get a new set of o-rings in there along with the metal flange. Some photos below.
Hope this helps! I'll probably do the same swap on my 2002 wagon as a preventative step. Not a bad repair, but also not one you want to deal with in an emergency.
Graham
