How to burp a radiator without a radiator cap?

Hi so I drive a 2001 Ford Escape XLT V6 2WD 3.0L and it's overheating. A couple of weeks ago my car started to overheat. I pulled over and it was sizzling and all that and when I got home I discovered my radiator was cracked. So I replaced it. I test drove it and it was still overheating. Yesterday I replaced the thermostat and test drove it. After about 6 minutes it warmed up and the gauge went to normal but soon after it went to the hot zone and was overheating. I pulled it into the garage and the only thing I could think of is the water pump until someone told me about there possibly being an air pocket in the cooling system. However, my radiator does NOT habe a cap… Only a reservoir. So before I go buying a new pump for $60 I want to try and see if an air pocket is causing the problem. So how do I do this when my car doesn't have a radiator cap?

I presume you know how to burp it in the usual way. You can do it by removing the expansion tank cap instead. It helps if you can park the car a bit nose-up, and have the heater set to maximum heat.

I doubt you don't have a radiator cap. That's unusual