I've had my GT4 now for about 7 weeks and have about 750 miles. (it's alot of fun; I'm never in the car as long as I'd like to be). Changed the oil myself a few weeks ago (first time ever in any car); I have noticed that the oil temp seems to be a couple degrees higher after the oil changes. Before it would max out a few degrees below 100, now it's a couple degrees above. Used valoline 20x50; I think the car had another 20X 50 in it before. Could there be a 5 or 6 degree temp difference between different oils? The oil is not low, in fact it may be high, alittle too much, but could having too much oil make it hotter? I would think the oppossite.
Mine started doing something similar (78 308 GTS) it was only a coincidence, the oil temp sender (Veglia) was crapping out. I ordered a new one from T.Rutlands for $14 (this was four or five years ago). Yours is probably going to...these cars are old...