All metal expands when heat is exposed to the area. Becasuse you have different material thickness, that plug could "float" and move around. I really never liked press fit parts like this in engines, because of vibrations and heat. Also, if your cooler starts to leak for what ever reason, it's not sealed this way. Coolant will still enter into your intake manifold. You need to seal weld the inlet and outlet flanges of the egr cooler to be effective.Oh ya, I forgot to say that I didn't even have to weld the stainless plug in the ERG cooler. I peened the end to keep it from being pushed into the EGR cooler, and when I did I used a vise to hold the plug. The vise left marks on the outside of the plug made the plug a press fit.