When it comes to heater cores, radiator caps, thermostats, I only use and sell those branded Stant.  I’ve tried those $1.99 radiator caps and they typically don’t last our warranty period.  We rarely find a bad Stant cap and when we do, it’s usually been damaged by someone trying to remove it and they didn’t know you have to push down and twist radiator caps counterclockwise to remove them without damaging them.  I also like that they have a full line of radiator caps, oil caps and locking and non-locking gas caps.  That way I can just stock just their line and have 99% of all the caps I need in stock.

Stant