Is it a heating problem, or not a problem at all??? Also engine knocking in "D"?

[stallion]

Hi all.

My SVX tends to heat up fairly fast, BUT it has never ever went past the middle of the temp gauge. I question if this is normal because on my sister's Nissan, it does not climb that high. I'm at the middle of my temp guage within maybe.. 10-15 mins of driving/idling. Again, it has never went past, but I always feel uneasy seeing it rise so fast. I felt it was T-Stat, so I went to go buy one (A Prestone one). But looking at previous threads, this one wont fit? ? ? Which AUTO STORE ones do fit? I only have 2 days to work on my car, so I can't wait for the OEM from subaru.

My second conundrum: the svx idles with a thump thump thump, consistent when im at a stoplight. BUT when I put the car in neutral, it goes away completely and it idles quietly. Obviously tranny related, but what can solve this problem?

THANKS IN ADVANCE for helping this N00B!!!!