Forgive me if I don’t know the technical terms. My car’s temp gauge always ran a little under the halfway mark. About a month ago, it moved to the halfway mark. Last week it jump to the 5/8s. The car never officially overheated, just ran hotter in increments. I took it to the local Tuffy auto center who has always done right by me. When I asked if I was being paranoid, I was told it should be checked out. The thermostat and radiator ended up being replaced. Picked up the car last night and asked how hot the car should run. Was told the thermostat shouldn’t go over the halfway mark. Driving to work this morning I noticed it hit the halfwaymark and stayed there, which meant it was running as hot as it should. But I’m paranoid. Should I be anxious about this? What if I get stuck in traffic? Should I take the car in again? I really hate being a single female in the automotive world.
First thing, good girl for watching the gauges. Engine temp is a killer.
Yikes, radiator replacements are not a common procedure. The thermostat might have been the only problem. Thermostats themselves are usually easily accessible with minimal tools and only cost about $10 last time I looked for one. Radiators will build up tons of crud over the years but most of that can be chemically flushed out.
You might want to try and pick up a simple auto repair manual for your make and model of car and a cheap set of basic tools. The books will often have basic system troubleshooting tips and demonstarate how to check the basic problems and perform preventative maintenance. You would be amazed what you can do in a couple hours in your own driveway and save lots of money 
Your message indicates that the car is running cooler now (halfway mark) than when you took it in (5/8ths). That tells me something has been accomplished. If you’re concerned about how it would act when stuck in traffic, let it idle at home for 20 minutes (after it’s warmed up) while you keep an eye on it. I would think that the repair shop did this before determining the problem was solved.
Cooling system repair is fairly easy, but the diagnosis can be very tricky sometimes. Although it’s possible that replacing either the thermostat or the radiator alone might have sufficed for now, it’s also possible that both were factors in the running hot, or that three months from now the other would have had to have been dealt with. It’s impossible to evaluate the diagnosis without testing the car as it was before the repair. Nevertheless, what you had done does not strike me as alarming.
Chemical flushes can sometimes be helpful as maintenance, although regular basic flushes done often enough make chemical flushing unnecessary. When hard deposits have built up in the radiator, flushing won’t help. Mechanical cleaning (“rodding out”) or replacement is then needed. Some radiators can not be successfully fixed (leak repair or rod out) and must be replaced.
Was told the thermostat shouldn’t go over the halfway mark.
The thermostat is in the engine. What you’re looking at from the driver’s seat is the temperature gauge. The correct terminology would be “the gauge shouldn’t go over the halfway mark.”
Sounds to me like you did fine, you addressed the situation before it became an emergency or a bigger, more expensive, problem. Congratulations for being an aware driver. Also sounds like the repair shop probably did fine, as well.
I called the shop this morning and talked to Mark, the guy who did the repair. He said that the gauge at halfway is fine but if it goes above halfway to bring it back in. I told him within 2 minutes of driving the gauge went to halfway and he said that is good and told me why (you want the engine to heat up quickly so that it’s fuel efficient). So I learned something. But I’m still going to be cautious. The radiator didn’t have to be replaced, but the sides were bulging and it was suggested that it be replaced now to avoid the “burst, coolant flood and car getting towed” in the near future. And FWIW, the intake valve was replaced last year because it was cracked and coolant was leaking into the oil So that’s why I watch the temp gauge.
The fluid needs/should be changed like every two years (read the instructions). You should also give us the year & model of your car so we know what you are talking about.
I don’t think 5/8 is extreme if the weather is very hot &/or you have a large load.
oooops. I meant the car manual not the instructions 