Zinc

[Ronan279]

Hi!
I was wondering if you knew what was that nut, I thought it was the Zinc at first. But maybe its not?
As you can see I have a lot of corrosion. I replaced the prop zincs, but not sure it's enough here.

Thanks a lot for your help!

[Sam]

Well on my boat it is a brass manifold drain nut that I remove to drain the manifold for winter storage preparation. Fyi every few years I clean up the threads with a thread tap and few more years change the nut when the softer threads get "rounded".

[Ronan279]

So no Zinc on the engine, right?

[Al Schober]

Engine itself has NO zincs. You should have a zinc in the vicinity of your prop.
If you have glycol cooling, the HX should have a zinc in the raw water side.
edit: That snowy street ell looks like a galvanized steel fitting that has corroded externally due to ambient conditions. I'd be concerned about it's internal condition and recommend replacement with a bronze fitting (brass if you can't find bronze). You may also want to consider making that fitting the INLET to the manifold. Let the other (high) end be the outlet.

[sastanley]

What Al said...We call it the "Thatch mod"...most of us A4 enthusiasts agree with forum member Thatch, that you should take the cooling water from the t-stat outlet and plug it into the aft (lower) end of the manifold to force the water uphill and provide better manifold cooling, before it spits out the top of the manifold and off to the riser/mixer/HX.
Photo for clarity. I have clycol cooling, but I would recommend the same route with raw water engine cooling. If your motor is RWC, send the exit from the top of the manifold to the exhaust riser.