White steam/smoke coming from hood of car and car occasionally overheats?

It's a 2000 Honda Civic.

Over the last 6 months I have replaced the radiator, radiator hoses, and gasket. I had some trouble a few days ago on a road trip and was told I had air in the system. They fixed it and she drove fine for the next couple of days, but then started overheating again. I pulled over, put in a little radiator fluid and she was fine for the rest of the trip - going full speed, stop and go traffic, everything. Haven't had trouble since, except there's this white steam (that smells funny. Not sure how to describe it) coming from under the hood more and more. The car is not overheating when the steam is coming off.

My suspicion is that I put in the wrong combination of coolant and water recently (before I bought the pre-diluted stuff that I've used since) and that that is causing the trouble. But I know almost nothing about cars, so I can't be sure.

Any suggestions? I don't really want to take it back to a mechanic because I've been taking it to mechanics for the last 6+ months and they keep telling me different things. Thank you!

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