Throw that wrench away.  A good box wrench should be used here.
If you rounded the nut off enough and this will no long work, use
a small pair of vise grips,  and then throw the nut away when you get it
off.   That's only if you get it off without breaking bolt/stud first.
Heating it with a torch is the only good way of  removing very rusts parts.
                                Eric

Rocket J Squirrel wrote:

> I'm trying to pull the bottom cover off the passenger side of this 1.9L
> WBX engine so I can determine if a coolant leak is coming from the head.
> It is affixed to the engine in four places. I've gotten three loose, but
> the front (front is front) where it mounts to the exhaust port with a
> bolt is being tough. I have PB Blasted the bolt and let it soak, but it
> won't budge. All I can get on it is a 13mm open-end wrench . . . tips?
> Suggestions?
>
> --
> Mike "Rocket J Squirrel" Elliott
> 71 Type 2: the Wonderbus
> 84 Westphalia: "Mellow Yellow (The Electrical Banana)"
> KG6RCR
>
>