FM radiator cap

There are a lot of radiator caps out there, so how do you know you're getting a good one? Same answer here as elsewhere - buy it from FM. These are made with a silicone seal for long life and an anodized finish with a laser-engraved logo. Plus, they're much more economical than other options out there. 

Available in 16 psi or 20 psi versions. Most cars running at least 30% antifreeze will want the 16 psi version. If you're running more water you'll want the 20 psi version - 100% water boils at a lower temp than water + antifreeze, raising the pressure of the system brings the boiling point back up. Bear in mind that more pressure = greater likelihood of leaks. If your system is healthy it'll be fine with 20 psi, if it's questionable the higher pressure cap might push the system too far and cause a leak.