While swapping my parts over i noticed my GTO oil pan was cracked. To my surprise it hadn't weeped any oil out on the outside. It must be from a nut that holds my plastic skid plate to the steel plate and it may have flexed upward or a rock may have been wedged in there. Ill check the skid later and move the nut if thats it.
I figured this would be a good spot for some oil soaked cast aluminum repair tech.
Welding aluminum can be difficult enough for some even more so with cast aluminum and very hard to do with the common oil soaked cast aluminum. Most cast aluminums have some porosity which soaks up oils making it even harder to clean. After years of cast aluminum repairs i have found this technique to work the best for me.
First i try and get the surfaces as clean and oil free as i can with a wire wheel or a grinding wheel. In this case all i used was a wire wheel. The oil will soak into the crack and as soon as you light up with the tig it will be sucked out into the puddle you are trying to establish and ruin any chance you can of welding it. I will simply run several "Dry"(Not adding filler) passes over it with the tig and wire wheeling in between. Each time you run a dry pass the heat and cleaning action from the AC current will float the impurities to the top where the wire wheel can reach them.
This is the result of 4-5 dry passes. All the oil has been sucked out of the joint and aluminum is fusing together with each dry pass. Its okay that the cast is cracking as i have not added any filler to it yet and the pan is still getting a good pre heat going. After running several dry passes on both side of this weldment they will achieve full penetration without any grinding or beveling of the joint.
Out side of the pan after the first dry pass. After 3-4 passes i had it as bright and clean as the inside.
After they were nice and clean i laid in some 4043 filler. It has never let me down with aluminum castings.