Site: Partypoker
Stake: $0.1 / $0.25

Hero's image at table: TAG
Previous significant hands:
1) AT utg v AJ SB - lose $5 with pair of T vs pair of J.
2) Jh8h co v 99 mid pos. Win $5 with heart flush on River Vs a set of 9's.
3) Call a big stacks $4 semi bluff with QTo on river, both have same hand & split pot.

Hero: AcQc (utg) $26 stack
Villain: $30 stack, TAG (mid pos)

Preflop: call BB utg.
Villain raises to 4x and I call.

Flop (heads up): 6c 6d 8c
I check the pot expecting him to cbet into it.
Villain checks behind.

Turn: Jc
I bet half pot and get called after a short pause

River: low club
Villain bets $1.5
I raise to $4 for value.
Villain reraises all-in and I'm covered.
I call and villain shows 66 and wins with quad 6's.

I didn't think about full houses or above on the board, since I thought that with my hand it was worth going all-in on.

How often should I call an all-in on the river in this situation?

Tink the 3 hands described are missing alot of relevant detail. We don't know when or how the money went in. E.g. the 3rd hand. Was that a call with Q high, top pair, middle pair? Was there a missed or completed flush draw? etc.

Should open preflop for a raise.

Flop is fine.

Turn lead is fine.

Having led the turn, I would lead the river too.

As you elected to checkraise the river you are showing a massive amount of strength. Is your opponent now going all in holding just the Kc or Tc for 2nd or 4th best 1 card flush on a paired board. I think not so got to fold to the all in as played.

It is a fold on the river because you are often crushed.