Radiator ,Thermostat,or Water pump ,which to go after

[chasinthesun]

The 84 300cd was in need of some radiator fluid service and had been ready to get going on it when I noticed a bit of yeh olde rusty water when drained.I revisited the auto house and returning with some radiator flush ,prestone brand.Drained radiator ,readded clean water with additive and ran as directed with the follow up of the flush ,then repeat .So basically ,in short ,I took a trip and had the system boil at the reservoir at pit stops,the gauge wasnt pegged ,actually set at an acceptable temp.After returning I decided to take out the thermostat and drill 6 holes in the t-stat thinking that would do it.Same result,top small house puffing into reservoir after just 2 minutes of running.I did notice the radiator ,while the engine was stopped ,was cool at the bottom .Next step , give the radiator shop a call for service ,or replace the water pump?