Update; Radiator spewing and limp mode fixed, with pictures.
 

The new OEM arrived and it is not the same as the aftermarket one. The bypass valve is only open 1/8" when cold and the main valve opens after boiling. See pics;
http://i661.photobucket.com/albums/u...%20pics/t1.jpg
This picture shows how long the bypass valve is and it restricted the block circulation flow. New OEM on left
http://i661.photobucket.com/albums/u...%20pics/t2.jpg
This shows the Motorcraft one on the left fully open and the bypass valve is now extended more than the other which directs all the water through the radiator.
http://i661.photobucket.com/albums/u...%20pics/t3.jpg
This shows the old one (actually new) finally opening after 5 minutes of boiling.
http://i661.photobucket.com/albums/u...%20pics/t4.jpg
This is what the bypass system looks like that warms the water faster in the engine before it is all directed to the radiator. Here is some reading on it;

http://www.are.com.au/feat/techt/thermostat.htm

<cite>You will have to copy and paste above into Google etc to see how the bypass works (A R E Cooling)</cite>
<cite></cite>

Dang. LOL.

I guess the thermostats are generally so much better now that we tend to forget about them.

Good Job finding it!

Remember how thermostats used to go on vehicles 30+ years ago all the time?


I can't think of more than one in the last 15 years that I've replaced!

REP TIME!!

Edit: crud. I'm in replock on ya.

Thanks anyway:-X22

Great info.
glad i usually buy oem for the less expensive parts.
just not worth saving $10 sometimes..

Hopefully that fixes the problem. It's amazing how the little details can make such a drastic difference in performance. I got him for you Bion. :-X22

So the moral of the story is when you need a new thermostat buy the Motorcraft one? Glad you got it fixed.

Right, for $9 and free shipping from Ebay it could have saved my engine. (they don't sell them in this town). If they don't work right temperatures can quickly go very high which is why they came up with the fail-safe/limp mode feature.

So no more limp mode?

Stewart

No, it's all good now. The aftermarket thermostat was opening at 212 degrees and it will limp out at 205-210.