I installed new gaskets including the upper plenum-to-lower intake manifold on my D2 about 4-5 months ago and when I disassembled yesterday I found oil residue in-between the bottom of the gasket and top of the manifold. I had the bolts torqued to spec and a bit of gasket adhesive on the top of gasket to bottom of plenum for ease of install. The residue just wasn't around the rim of the holes but a much larger surface area almost hole-to-hole in 2 different places. Is performance being affected with the gasket not being sealed on the entire surface and should I be using some silicone gasket around the holes? The gasket has a raised, textured surface on the top of it, but not on the bottom. Its hard to see the raised, blue material encircling the holes on the top portion of the gasket for positive seal. nothing on the bottom so maybe I could dress that up a little bit if anyone can confirm. I am not reusing the old gasket, I have brand new one.

 

I use the copper gasket spray, if it is not sealed, it will cause lean codes. There can be oily residue, because the oil vapors are pulled from the engine, via the tubes on the valve covers.

 

I didn't use anything the last time, and I never had any codes. I had some blue gasket maker but didn't pull the trigger as no one replied for hours while I was thinking about scraping all of that **** off the next time I was re-assembling. I also watched the AB video to get the torque spec of the bolts and he didn't use anything on the gasket either. Hopefully everything works out the same as last time.

 

It should be fine, I am creature of habit. Kind of old school when gaskets were just paper, cork or bare metal.