Given what you've said, I'm calling. If he is playing loose enough to see 50% of the flops, there is a good chance he paired his 3, 5, or 8 (in which case you'll almost definitely outkick him), or he has a flush or straight draw, or just has overcards. I would think the chances of him having what I just said are much higher than him having a higher pair. Given that he limped in, he probably doesn't have it. I call. If he hit two pair, a set, or A-8, then so be it. I'd never fold top pair top kicker to a very loose very aggressive player who had just gone over the top for all in with only overcards.