What's the difference between the two? I'm looking on Atkins for a new thermostat housing and the Automatic Tranny thermostat housing is almost 20 bucks cheaper? Is there a difference between the two? If not, I'll just get the cheaper one of the two but of course I don't wanna be making a mistake...

Any idea?

 

Interesting!
At first I was wondering WTF is this guy talking about..but I checked it out..lol!
Look real close at the pics and you will see the cheaper one has a threaded portion at the bottom for a sender,while the manual trans does not.
NOW,This is something to Consider.
They both are the same physically BUT if you plan to run a Temp gauge you can use that threaded hole for a Temp Coolant gauge.
If you had the one without the Threaded hole you would have to use a upper hose adapter.
While that location is not the BEST to place a sender it will tell you when the engine is hot When the Thermo is fully open.
IF you get it and don't have a gauge ready then you will expect to have a PLUG that is metric and can screw into that location until you do get a gauge...or your coolant will just leak out..hahaha!

If you just plan to keep it stock then use the NON threaded one.

The Sender is for auxiliary fan which is not on a 5 speed N/A.It is however on a Turbo..for something..not Real sure so I won't feed ya bull.

I use that location for my Temp gauge.I also have an adapter on my upper rad hose.(ya,progressive build stuff..here and there..)

The BEST location for a Temp sender is at the back of the water pump but that entails drilling and tapping for a sender.

OH..note that the Thermo NECK (that is what they are usually called) is Series specific.
The S4 and S5 can't be switched as the s4 has a 2 bolt mount and the s5 has a 3 bolt bolt.They need their respective waterpump housings to mate to them.

 

I see it now. Interesting! Thanks for the input!