I had a similar problem when I picked up my car. It would never get above 80 and took a while to get up to "your red line". After doing some reading here and finding out that it is actually better to err on the hot side (as long as it is not 100+) I decided to open things up and have a look.
I found my thermostat was eviscerated. Someone had ripped the guts out and just used kept the outer piece to use because of the seal. Running cold all the time is NOT a good thing.
Later I found out my fan clutch had failed at some point and the morons put a bolt through it to help the cooling. Long story... And caused more problems (for me) in the long run. The failed fan clutch is probably the reason for "removing the thermostat". They just were not smart enough to figure it out.
Hopefully whoever put the bolts in your new thermostat housing used anti-seize. Steel bolts + Aluminum housing = corrosion. If anti-seize was used and they were "torqued properly", removing it (or any bolt in aluminum) should not be a problem. Most of those problems arise from rushed jobs with improper tools, improper materials and the old "calibrated arm syndrome" (IE: no torque wrench).
Today, I was outside looking around under the hood and found another botched repair job. The hose barb running out of the top of the radiator was leaking. Someone at some point managed to mess this part up as well and installed an improper hose clamp, return line, etc... Another mess I had to deal with.
I guess the bottom line is this. When every you decide to take time to "delve into" your cooling system on one of these cars.... Take your time and do it right. Look at the entire system closely. God only knows what you will find later if you don't.
