does he us a band or penis ring to hold his erection. If so it will feel cold when entering you
i will try all that, probably LATER THAN SOONER, I have to ump on to him. i will post the results
I don't think vaginas change temperature very much, especially if you are as aroused as always. It is probably more in his perception than in your vagina. If you would like to try some scientific testing, get a basal thermometer and take your temp after sex for a while, and see if your temperature varies. He might himself be getting hotter, which would make your vagina feel cooler by comparison, so take his temp too by lying the thermometer to the side of his penis when erect. I know, to be scientific you would have had to have readings from the old "hot vagina" days, but it still would be interesting to see if there is presently a lot of variation.
The other thing that comes to mind (especially if you don't think it would be entertaining or amusing to take temps) is, if he suffers from low T, perhaps he is not rushing to put the penis in immediately when he gets the erection compared to the fevered old days? If so, again, the penis could be warmer on erection now because it has had more time to heat up, than it was in his younger days when he would just poke you as soon as he was up.