Recently replaced radiator, can't fill with all 3.5 gallons of coolant

I recently had a local freelance mechanic change my radiator in my 98 LE 6 cyl 3.0, he only put 1 gallon of coolant because I bought the coolant and misunderstood I needed to buy 4 gallons, I've tried to add the additional gallons but it's filled up, I've burped it with the heater at full blast like your supposed to but it makes no difference, there doesn't appear to be a bleed valve on top of the radiator like I've read there is supposed to be, is it possible there is still coolant in the engine from before and that's why I can't add more? I've been able to drive it a few miles with no overheating although I"m not sure about the cooling fans, the seem to only go on when the AC is on, could it be a bad thermostat? I need to do some further testing. All this going on while I"m having a nightmare going on with the break booster hard lines and radiator coolant lines rusted on my old motorhome I'm living in. Murphy seem to be falling me around or Mercury in Retrograde if you are familiar with that. Thanks for any info.