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Rear Coolant Flange - OEM vs Aftermarket?

6K views 28 replies 10 participants last post by  PZ 
#1 ·
Good morning - it's been forever since I've posted on here, but I had a recent repair that has me asking a question.

At the very top of Old Priest Grade on Highway 120, my rear coolant flange decided to fail catastrophically and dump all my coolant. Luckliy, I was able to immediately turn into a cafe, eventually got towed home, and replaced the flange yesterday. Once I got it off, I saw that it had split along its entire length horizontally.

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Now that I replaced the flange and all the other O-rings, I'm back up and running, and even have a spare flange in the trunk now in addition to the spare coolant I already had there.

My question is this: For those of you that have replaced this flange, have you had issues with both the Genuine VW and aftermarket parts? Or do the Genuine VW ones hold up better? I had replaced what was probably the original (not sure?) flange a few years ago with a Meyle flange, and that was the one that split open. The one I just bought is made by URO, purchased from the same local foreign parts supplier (basically a WORLDPAC source).

I saw in a couple previous threads about these the recommendation to use only a genuine VW part for this, and I'm starting to wish I did that. I think they are $20-30 as opposed to the $6 I payed for the URO one. I would hate to have this one crap out early and strand me again when I could have replaced it with a genuine VW part that will likely outlast it. Also, it was such a pain to replace (and I have the simplest engine of the 1.8t series, an AEB) that I don't want to do this again if I can help it.

Thanks in advance for any advice and recommendations!
 
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#2 ·
How many miles has it been since the last water pump change? If it's been over ~125K or so, you may have an opportunity coming up (keep an eye on whether coolant level is dropping). That split coolant flange looks like somebody got a little frustrated while changing their CTS. ;)

If you torqued both bolts on the coolant housing flange using a torque wrench, you should be all right. But try to limit the time spent in traffic jams to no more than 1-2 hours (in CA :rofl:) before you have a chance to change it.

:beer:
 
#3 ·
I don't recall ever paying $20-30 for a replacement flange, even ones from a dealer. I generally order them online from ECS Tuning or other reputable parts retailer that doesn't usually sell the cheap crap. I've never had a flange fail catastrophically like yours. I'm on my 3rd or 4th flange on my '99 Passat, all due to O-ring failures. I've also replaced them on a '02 A4 and a '98 Passat. The parts are cheap enough that it pays to replace the flange, O-rings, clips, and plug all at the same time. I rarely get the bill high enough to qualify for free shipping unless I order other stuff to fill out the order.
 
#5 · (Edited)
Electron Man: I changed my water pump when I replaced my timing belt about 30k miles ago, so I hope that doesn't need replacement for a while. I hadn't touched this flange since I last replaced it, so I have no idea why it split like that - there is a sort of molding seam there from the manufacturing process (probably injection molding?), so perhaps that acted as a stress concentration point and allowed it to break more easily there.

captain_video: I replaced all the o-rings at the same time, so those should be ok for a while. I was careful not to pinch the o-ring from the hard coolant pipe to the flange, since I did that last time I replaced one of these.



That's a great idea! I didn't know that metal version was even available! For now, I just needed to get back on the road so I could get to work. Now the only question is, do I want to re-replace the part now that I just spent a couple hours yesterday putting it in? $50 is pretty cheap insurance against having such an important part fail again.

Thanks again for the replies so far!

EDIT: I ordered one of the cast aluminum rear coolant flanges from UROTuning and will try to remember to report back once I have it installed. The O-rings can still fail, but overall, I see much less chance for anything to go wrong with this part.
 
#6 · (Edited)
I received my aluminum flange from URO tuning, but have yet to install it. The quality seems good, so I'm excited to put this part on. One thing to note is that the flange does not currently come with the O-ring that seals against the hard coolant pipe (part # 058121687). I contacted their customer service, and they are sending me one of those o-rings, and I believe they will be adding it to the part so that it comes with it.

EDIT: They have updated the part page, and it now includes the O-ring from the flange to the hard coolant pipe! http://www.urotuning.com/Cooling-Flange-in-Cast-Aluminum-B5-1-8T-VW-Audi-p/058121132c-cast.htm

From reading a couple other posts, it would also be a good idea to replace the lower heater hose o-ring, which apparently doesn't have a separate part # in the EKTA. That o-ring is apparently 21.3mm ID x 3.6mm W or 22.0mm ID x 3.5mm W. I think a new o-ring comes with the replacement heater hose, but I have not (yet...) had a problem with that hose, so I haven't replaced it yet.
 

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#7 ·
I've got the same flange sitting in the garage to install on my car some time. I also picked up a 10 pack of the heater O-rings from JC Witney as I expect the hoses will leak once removed (they almost all do).
 
#8 ·
After driving with the temporary plastic flange for about a week now, on my way home from work today the lower heater hose decided to pop off. I pulled over, reconnected the hose (Ow, very hot!) and tugged on the hose a little to make sure the spring clip seated properly this time. Refilled with coolant and was on my way.

I think I will get a chance to swap the metal flange on next week sometime.

Moral: it is hard to see, so double check to make sure that lower heater hose is seated properly and the connector clip is engaged when replacing the flange!
 
#9 ·
I finally got around to swapping in the metal flange from UROTuning today after work. Was able to take a different car so this one could stay cool to work on. Changed the temp sensor too, since the old one had a crack in the plastic. The new one is the part number of the blue 4 pin one, with the correct plug shape, but is a green color. Seems to work fine. No new leaks yet! (Fingers crossed...)

Now the next weakest part in the cooling system can break!
 

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#11 ·
Everything lined up fine, and it is working fine so far. It was nice that it came with two Allen head bolts that go to the cylinder head, since it is easier to tighten that on the top bolt that is just barely under a hard coolant pipe.

One thing I would have done differently during the swap: drained the coolant first. I thought I would only lose a little coolant, but ended up making a mess on the garage floor.
 
#14 ·
Here is the O-rings I ordered, it was actually from Grainger, shipping was expensive, they did not give an option of ground:
GRAINGER APPROVED
O-Ring, Dash 212, Buna N, 0.13 In., PK10

Item# 5JJT3 Mfr. Model# 5JJT3 Catalog Page# 2711 UNSPSC# 31181506


I still have not installed my flange, but my old one is not leaking yet.
 
#16 ·
I had intended on replacing that lower heater hose o-ring, but the one I ordered when I got the flange was not the correct size. I just wanted it back together, so I didn't go to the hardware store to try and find a replacement.

Also, to Captain Video - that's a good point about the different type of bolts. The thing I like about the allen heads in this application is that you don't have to mess with that upper coolant pipe as much. I kept having trouble with getting a socket over the head of the bolt, since that pipe would be really close/pressing on the bolt head, and it was a blind operation at the back of the engine. I've rounded out a few of these allen style bolts (including the ones that originally held on the AC clutch, which I then replaced with hex head bolts), so that is a concern. I'm hoping that I won't have to monkey with this flange for a very long time now that this aluminum one is in place.
 
#18 ·
I use a 10mm 1/4" drive deep well socket to get at the bolts on the flange and hard pipe connections. A short extension may be helpful to get at the hard pipe bolts on the side. I can lean over top of the engine and access the flange bolts if I slip my arm around the passengers' side of the engine and reach around the back of the block. I loosely install the bolts on the hard pipe first and then do the same for the flange to engine block surface. That's always helped me to mate the hard pipe with the flange and not have any leaks. If you remove the temperature sensor from the flange and move the cable assemblies out of the way you can see both of the flange bolts quite easily, at least you can on my '99.

Unfortunately, when I installed the new flange to heater core hose today, the hose still leaked even though it was a new hose. I ended up putting the old plastic flange back in. It still leaks, but just a slight drip. Somehow I managed to lose the O-ring on the metal flange, which is why I went back to the plastic one. I've ordered some extra O-rings from ECS Tuning to have them on hand.

Does anyone know what size O-ring is used in the heater hose that connects to the rear of the flange? I can't seem to get mine to form any kind of proper seal even though it's fully seated and clipped in place.
 
#21 ·
I successfully installed the new genuine VW flange & o-rings with no leaks. My original 14 year old flange looked okay but the flange to head o-ring was mushy & leaking.

I did one big thing different from the DIY guides: I took a few extra minutes to disconnect & remove the coolant hard pipe from the car. I could then easily connect the flange to the hard pipe perfectly straight & evenly tighten the bolts. Also pre-installed the CTS o-ring & sensor on the flange outside the car. Then I snaked the flange+pipe back through the nest of vacuum & pcv hoses and bolted the flange to the head.

The -212 size o-ring fits the heater hose connector perfectly. HOWEVER, BEWARE of the plastic ring in the connector not seating all the way down. The ring should fit tight against the o-ring with no gap, but there is a lip inside the connector that keeps it from going down far enough. I couldn't get the ring past that lip with any amount of force. I finally got it to go past the lip at an angle--just be very careful to not dislodge the o-ring. I think this is the cause of most problems (leak or popping off) with the heater hose connector.
 
#22 · (Edited)
Success!

I finally got the new flange installed with no leaks.

WARNING!!!

If you install the aluminum coolant flange you need to check for any ridges along the casting mold lines as shown in the photos below. The photos show the areas I had to file smooth to eliminate the leaks.

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Pipe Auto part Tool accessory Asphalt
Auto part Pipe Tool accessory


I pulled everything apart and inspected the O-ring inside of the flange to heater hose and noticed a nick in the O-ring. I then inspected the aluminum flange and discovered some flashing that didn't get cleaned off at the seams of the mold. One of them was rather large and quite jagged and nicked the O-ring as well as creating a gap between the fitting and the O-ring, which would account for the new flange not sealing properly. The nicked O-ring caused the hose to continue leaking when I reinstalled the old flange. I took out the O-ring from the hose, flipped it over so that the nicked portion was not exposed to the fitting, and reinserted it into the hose. I had new O-rings for the flange to engine block, temperature sensor, and hard pipe connection so I installed them. I tightened everything down just snug and filled it with coolant and crossed my fingers when I started up the engine.

Eureka! No leaks!
 
#24 ·
I used a Uro Parts flange on the 1.8t 02 AWM variant wagon yesterday. I bought a new o-ring for the hard pipe connection at the VW dealer.

Dealer did not have a separate o-ring for the heater pipe connection, so I just re-used the original oring. Would have had to buy a whole heater hose for $119 to replace the o-ring.

I fixed the leak on the back of the head, and no leaks at the heater pipe or the hard pipe, and no leaks on the new temp sensor (beck arnley).

All high and dry right now, knock on wood.
 
#29 ·
The plastic ones are OK, but I have had a couple of aftermarket ones that did not seal perfectly. Then when replaced with an OEM one, there were no leaks. On my own car, I put the Aluminum one on, but smoothed out all of the seats for the O-rings with a little sandpaper. No issues since then.
 
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