villain is 31/18 on 108 hands, rfi btn 1/1, fold to cbet 5/6. is this a good spot to 3 barrel bluff?

No, It looks very spewy.

Majority of time you will be called on the river brick if they call flop+turn, this is quite results oriented.

Q 8 suited may be a slightly wide defend pre, although I don't mind it, especially if player to the right has been raising from the button often etc. I think you can c-bet one street here, I would think about a delayed continuation bet here, on the turn, as you pick up at least some equity. (problem being that villain will bet out at flop when you check very often, at which point, its fine to give up). the only piece of information you have here is that he is on the btn and MAY be raising light pre-flop. This is not enough information to turn you're hand into a 3-barrel bluff. This is also not the ideal flop/board to be bluffing - I think you may have gotten quite lucky for him to call 3 streets and let it go on the river.
Did you have any reads on the villain here?

I like everything until river, this is total brick and he really rarely folds on it

so you guys don't think he will fold a small ace?

Yeah. OP you represent an extremely thin value range (like AJ,JJ, I guess KQ). I doubt you get JT and AQ to fold river very often. If villain actually calls you down and then folds the river with a weak A in this spot it's a pretty terrible play so I wouldn't expect it to happen very often.

Spew