[VCPwayne]

I need to make some ground clearance so milling off about .750" off the bottom of a NEW oil pan and welding in a plate. The casting is new so there will be no oil to contend with but other report that the pan is an alloy that isn't that clean. What rod will give the best results (ie: no leaks)?

[Coldman]

I'd be using 4047

[Oscar]

I agree that sounds like a good rod to use for leak free joints.

https://www.esabna.com/us/en/education/ ... -alloy.cfm

ESAB Knowledge center.
What are the advantages of 4047 filler alloy?

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Q - I have been informed that there is a filler alloy (4047) that can sometimes be used in lieu of the commonly used filler alloy 4043. What are the advantages of using the 4047 filler alloy and when would it make sense to substitute it for filler alloy 4043.

A - You are correct there is a filler alloy 4047. The filler alloy 4047 was originally developed as a brazing alloy (BAlSi-4) or (718) taking advantage of its low melting point and narrow freezing range (1070 to 1080 deg F). The main difference between 4043 and 4047 is the silicon content of these alloys. The 4043 filler alloys contain 4.5 to 6.0% silicon and the 4047 contain 11.0 to 13.0% silicon. The higher silicon additions in the 4047 alloy result in improved fluidity (wetting action) during the welding operation. This characteristic has proven itself to be extremely desirable when welding thinner materials that are required to have leak-tight joints. Welding procedures used in the heat exchanger fabrication industry have been improved by changing from 4043 to 4047 filler alloy. The 4047 provides exceptional fluidity, which helps to reduce weld leakage rates during the manufacturing process, thereby substantially improving productivity. Additional benefits from the 4047 filler alloy over the 4043 are minimizing solidification cracking and slightly higher fillet weld shear strength. Other advantages have been found in moving from 4043 to 4047. One such advantage is improved cosmetic appearance, particularly when welding thin material. The improved fluidity from the additional silicon within the 4047 filler alloy can produce exceptionally smooth welds that are cosmetically pleasing. In terms of the AWS D1.2 Structural Welding Code for Aluminum, 4047 is acceptable as a replacement for 4043 as both of these filler alloys have the same “F” number (F23). The 4047 filler alloy like the 4043 is suitable for elevated temperature service. However, the same problem with 4047 as 4043 can occur if post weld anodizing is to be performed. Because of their silicon content, both of these alloys will typically turn dark gray after anodizing, and for this reason, they are usually not recommended for products requiring this type of post weld surface treatment.

[VA-Sawyer]

For thin stuff, I agree with the 4047. However that cast Aluminum oil pan isn't what I consider thin. I have used both 4943 and 4047 on cast . For that job I would choose the 4943. It would be best to know what alloy the pan is made from. The amount of Silicon can have an effect on short cracking.
If you shorten the pan , remember you will need to redo the oil pickup screen too.

[VCPwayne]

Thanks guys!