Coolant leak, behind engine. B6 1.8t

[jfirko]

My son's a4, 1.8t b6, has developed a coolant leak. Just noticed since cold. I first saw a small puddle on the ground after it was parked in the garage. I have topped off the coolant twice in a month, just keeping an eye on it to be safe.

Looking in the engine bay I cou see some coolant back behind the engine. Any advice on the most likely culprit?

[jfirko]

Not sure how to post a picture. I may not be able to yet since I just joined.

[kevin1980]

Look at the coolant housing behind the engine

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[jfirko]

Thanks, I am suspecting that is where it is coming from. I purchased a mechanics mirror to take a closer look when my son stops home from college.

[walky_talky20]

If you want to fix it just once, I'd recommend a metal coolant flange. They are quite available and cheap nowadays:

Examples:
https://www.ebay.com/itm/15578643905...mis&media=COPY
https://www.urotuning.com/products/c...=8392239317047
https://www.ecstuning.com/b-iabed-in...-121-132b6~ia/

I've used several of the cheap ebay ones on my B5's and they've been installed for years for no issues. Much peace of mind to have a metal part back there.

[MoRbiD]

I had the same issues a few months ago. When I got the valve off I found it was that the O-ring failed.
Most likely due to a previous oil leak from a failed gasket. I already ordered the whole plastic part so I just replaced the whole thing.

The mechanics mirror will certainly help but you'll be working mostly by feel.

[jfirko]

Thanks, I imagine the added stiffness of the aluminum flange helps prevent leaks.

[walky_talky20]

Yes, they can warp (especially on the flange where they touch the cylinder head) or the plastic can actually crack.

[Gunnarrrrr]

I would avoid gimmicks like aluminum coolant flanges and steel water pumps. The reason the oem flange is the best, is the quality of the casting and the smoothness of the gasket surface. I've seen plenty of people fight with leaking aftermarket flanges and having to load it up with silicone. If you're worried about the plastic warping or cracking vs an aluminum one, keep in mind yours is over 20 years old. If you go oem, yeah, you'll want to replace it about 10 years from now again. But it won't come with any manufacturing surprises.