Do I need a separate pump or compressor to use this kit?

The pressure tester uses hand pump action — no external air source required. For vacuum purging, you'll need access to a shop vacuum or dedicated vacuum pump.

Will this work on my radiator cap or just the fill neck?

This kit adapts to the radiator fill neck. If you need to test the radiator cap itself, cap testers are sold separately.

Can I use this on a sealed pressurized expansion tank?

Yes — the adapter set covers most domestic and import expansion tank ports. Test-fit your specific tank opening before committing to pressure.