I have a small leak on the s4 top filler neck. It is on the two bolt flange that holds the top pressure cap in the coolant system. I replaced the O-ring and also used some gasket sealant on it and still it leaks at the exact same spot.

Its a very small problem but I figured I would ask if anyone has had a similar problem or any suggestions.

Perhaps I am under/over torquing the bolts.

 

The two bolts that hold the neck on, or just the filler cap mount with the pressure relief outlet?

For either case, take off both parts, sand them SMOOTH, make sure anything that's going to contact RTV is flat. clean it up super well, I used a wire wheel on my setup.

Finally, make sure you get the special high-pressure, high-temp, water resistant RTV (http://proseal.supergluecorp.com/80006.html) something like that. Ask a friendly mate at Schucks, Autozone, or wherever for some water-resistant RTV, they'll lead you to this stuff.

Once it's clean, shiny, smooth and flat, let it dry thoroughly. Put a thin amount of rtv on both faces of what you're going to seal, and press it on, then bolt them together lightly. Don't use enough pressure to squeeze all the RTV out. After its dried (about a 30 minute time period iirc) you can torque the bolts to spec and try filling the system. Make sure to keep coolant on you at all times until you're sure it doesn't leak anymore. Also I recommend warming the car up at a standstill to make sure that your seal holds at full pressure.

These are the steps that I use, and I haven't had any of my seals leak yet.

 

Make sure there are not any cracks either. Probably not though, but jsut check anyways

 

Yea that is why I am frustrated. I did exactly that. took it apart sanded it down, cleaned it up real well. Used Blue RTV, tightened, torqued and even waited 10hours before I started the car.

I can't see any cracks but the way it seems to be leaking from the exact same crack I wonder if that is a hairline crack in it or something.

 

Make sure your thermostat is seated properly, oem thermostats are highly recomended.

I talked with a rep from permatex. The proper way to use it is to not torque it down, jsut bottom out hte part. Then let it cure for 24 hours and then torque it down. I personally never had the time to do this, but that is supposed to be the best way to do it

 

where the 10mm Bolts go into the plastic thermo Cap housing have small brass inserts on it.you can't see them unless you Flip the Piece over when it is off of the neck.Maybe it is leaking there?..suggestion,Buy another Piece..The Part sells for about 20-30 bucks tops,But it will also give you the Piece of mind that the Cap is sealing up too.

 

If you've followed all of the above steps and you still have a leak, I recommend ordering new parts from Mazdatrix or similar, you'll have the peace of mind that they'll work properly, not to mention they're cheap.

 

I decided to just torque it down hard as I physically could and it stoped.