c3 running warm?

Hey guys, I have a question about my 79 running warm. It gets up to about
230 at interstate speeds after bout 10 minutes or so. When I drop back to
side roads or under say 50mph, the temp comes back down. Now im smart enuff
to know that higher rpm + more heat, and vice versa. Ive already replaced
radiator, water pump and thermostat(185) . The exhaust smells fuely, like it
may be running a little rich, or possibly retarded causing the engine to run
warm??? Is this a normal temp range and is there something Im overlooking?.
Btw it does not have the lower front spoiler and im wondering if that has
something to do with it. Any thoughts?
Larry in Va Beach