Radiator leaking

For the first time I saw the low coolant symbol light up on the display. Checked it and yes it was low (slightly), topped it off about a week later same thing. So I start to look around, found coolant weeping down the passenger side top of radiator - like the edge seam of the tank and core. Not sure if it a repair is possible. Looking around at prices (ECS Tuning) lists the RS6 (4B3 121 251F) $1371. I checked the p/n of the regular 4.2 C5 - it is 4B3 121 251D for $548. Are they not the same ? Usually the last digit is a revised p/n. Anyone had to replace theirs ?? Options ??

The radiator is most definitely specific to the RS6 and not shared with any other trim level. Your options are limited for replacement. They may still be available from Audi but I've seen plenty of parts on ECS as "in stock" or "ships in x business days" only to find out it was discontinued. Also, don't be fooled by aftermarket suppliers. You'll find that it will be missing an additional coolant port.

I just found out that Shokan is no longer in business...

Scour the part-out ads, ebay.co.uk/.de, etc. Or buy a running car for <8k with a blown trans then cannibalize it to keep yours running for a few more years. I say that in jest, but it's seriously becoming one of the few remaining options.

I've never come across a shop that will/can repair plastic end tanks/seams. Ymmv.

Best of luck!


https://www.ebay.com/itm/OEM-C5-Audi...gAAOSwmPFcrmya

They are definitely different. I think the RS6 is a Modine unit and it's all metal. I would suggest you find a legit old school radiator shop to take it to and see if they can repair it.

FYI, the non-RS6 4.2 radiators can be found cheap on the used or aftermarket and will work if you remove the afterrrun system. The radiators in the cold climate areas were the normal 4.2

Steve, do you know if there is a MT radiator for those of us with the 6spd now? I would think we'd want something a little larger than a 2.7t or 3.0 radiator.

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Originally Posted by hahnmgh63

Steve, do you know if there is a MT radiator for those of us with the 6spd now? I would think we'd want something a little larger than a 2.7t or 3.0 radiator.

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It seems that all the 4.2 radiators have the loop for trans cooling (or warming).

I haven't really done any research to see if the C5 S6 manual in the Euro III zone cars had manual trans cooling similar to the allroad or not. If not, then this would be the only OEM radiator I could think of that may not have the trans cooling built in. If it were the case, then you would still need to ditch the afterrun system.

...Although I've seen some specs on radiators with the third outlet on the bottom left that goes to the afterrun pump. I think they may be from C6 or B6 cars, though.

I'm sure it's possible that there may be one out there that would fit, but it would take some research.

I wonder if you could replace that third fitting with a tee off the lower radiator hose. I know it's a bit kludgy, but with the huge price difference between the regular 4.2 radiator and the RS6 version, it might be worth it. I also worry about long-term supportabilty since I suspect RS6-specific parts are going to go out of production faster than more common models.

There is also the full-custom unit someone had built by Wizard Cooling. I think the price was about $800, and I'm sure they could build a manual version that might even be cheaper. They are all-aluminum so should be fully repairable in the long run.

Anybody remove the after run system? What happens to the coolant control valve?

SteveKen did a lot of research on this stuff in his S6-RS6 conversion: http://www.rs6.com/showthread.php/25...l=1#post259812

Steve, did you ultimately remove the afterrun system?

So I tried a repair with a 2 part high temp epoxy on the crack (plastic side). I did not hold. So now it looks like a replacement.

Pulled the radiator out this weekend kind of a project. Tried really hard not to have to remove the A/C condensor coil - ultimately had to. Lost about 1 Qt of Trans fluid from the radiator and the disconnected line, also about a table spoon or 2 of AC compressor oil. New radiator arrives tomorrow.

Attachment 18968

Picture of Project

Got the new radiator in yesterday, kind of a PITA. I wound up buying it form audiusaparts.com - went with the OEM (not really a aftermarket option, unless you go custom). There is a place in Oregon - Ice Box that will build a custom one for about $1K and 5 - 6 weeks + they would need the old one and quite possibly the car. The one I got was $1069 and was actually built in 2017 (the date code sticker on it). The OEM is available but not sure for how much longer, when I got mine it was 1 of 2 left in the US.