Check engine light came on. Noticed temp needle was barely moving. Plugged in OBDII. It said something about thermostat circuit. Or something like that. I'm not real handy with the obd tool, so I don't know where to start. Please

 

What was the code associated with it, without it, it's hard to help you without knowing that.

 

It says P0128 Coolant Thermostat ( coolant temperature below thermostat regulating temperature)
Sounds like it's telling me to change out the thermostat... can't be that simple!

 

If it's just the thermostat then it's pretty simple to replace. Here is a thread about installing a thermostat housing however the thermostat is in it.

http://www.allfordmustangs.com/forum...-how-pics.html

 

It could be the temp sensor that fits into the thermostat housing...u can get one from your local auto parts store (Oreilly, autozone,etc.) for around 15 - 30 bucks. Since the thermostat doesnt actually have sensors on it and is completely mechanical I dont believe that is the problem, it's most likely the temp sensor since you said the gauge is not moving at all...while you're there replacing the sensor you might as well replace the thermostat if you haven't ever done it...Let us know the outcome.

 

If you replace the thermostat, get yourself a replacement housing, too. Ford made them out of plastic and it's a common problem for them to crack and leak.

 

Nuke is absolutley right, the lower thermostat housing is a POS design, in 100k I've replaced mine twice already. If you haven't done that yet it would be a wise choice to replace it along with the sensor and thermostat as well.

 

Yep, a POS! I am planning on replacing my upper and lower thermostat in a couple of months!

 

You gonna go OEM or is there an aftermarket one out there? I would love to get my hands on an aluminum one or at least a plastic housing that's made from one solid mold.

 

From what I have read, no one has located an aluminum one. I guess the plastic OEM is the one I will have to go with.