1996 Dakota 4WD Auto 3.9L v6
I am embarrassed to have to ask this...

I just replaced my thermostat as the engine was overheating after running around 20 min in traffic. I set the new t-stat just like the old one was. Same trouble exists. I easily could have inadvertently messed the prior one up when I did the head gaskets last Fall, as my normal commute is only a mile and I rarely if ever drive the truck more than several miles.

So... which way is the darned thing supposed to go in? (Quit laughing...)

Edit: For what dignity I might have left, I presume spring-side down into the engine...
Edit ii: I replaced the water pump about a year ago-
Edit iii: Ignore this for now, will repost if problem persists. Somehow the thermostat, ummmm, jumped, and was spring side up...

 

Yes, as your Edit iii says, spring-side goes down.
Hope that works out for ya!
Don't fret, we all make mistakes! (Believe me, I've had more than my fair share!)

 

Yep, spring side down. I always like to test them on the stove with a pot of boiling water. You can use a thermometer to make sure it's opening at the right temp.