Are those people beneficiaries on your life insurance policy?

In the first place, your car doesn't have a radiator cap, it has a pressurized reservoir cap. There is no discernable flow through the reservoir.

Another thing to check is the thermostatic clutch on the belt driven fan. I don't know how to check it other than to listen for it to engage when it should.

Sixto
91 300SE
87 300SDL
83 300SD