newly built 416 getting warm

I don't believe you have an issue if the temp never gets over 220. Modern FWD cars get up to 210 before the electric fans even start going and they go to "fast" at 220 and regularly reach as high as 230 for a peak.

I run a 195 degree thermostat because the engine is more efficient at that temp, it cools fine. If you get over 220 after a long idling period, i'd start to get worried...but 218, then cools right off if you start driving again is not an issue IMHO.