I usually spend some time cleaning out a new oil cooler, even though it’s brand new, before using it. I’d rather flush any manufacturing left overs out of there than have it cause problems down the road. I also remove the tiny foam piece that is usually attached to it and install my own. Which is more dense and thicker to take up the space between the doghouse tin and the cooler. It really is important to get every bit of air passing through your oil cooler, rather than have it escaping past it.