I have a small crack on top of the radiator, what adhesive should I use until I can replace the radiator cause it starts to leak.

I would use a two part epoxy to hold a plastic patch in place. Scuff up the area with sandpaper so the epoxy holds. Use a little less hardener to allow the epoxy to move with the temperature change. Mark the patch at least one inch larger than the cracked area. Wait 24 hours for a full cure. And hope it holds. Replace the radiator ASAP. --- Meanwhile travel with an ounce of black pepper and jugs of water. If it leaks, pour some pepper in and top off the water. The pepper will find the hole, fill the crack and swell. It might not stop the leak but it will slow it down. It won't clog up the system like stop leak does. It got me home from the Glen when my radiator met the fan.

loosen cap a little its a pressure leak only ,maby