thermostat options
 

what do you use? who makes the best for d series motors with bolt on mods?

OEM is sufficient.

Even crappy tire fail safe thermos have served me well.

OEM will work best for your application.

i am thinking i might go for a jackson racing.. is there any down side to this?

i can only imagine that cooler temps will be more productive to prolonging a motor.

you imagine wrong. the engine's optimal operating temperature is what it is to facilitate proper combustion, keep all metal parts expanded to their proper tolerances to keep mating surfaces within spec, keep oil viscosity optimal at its operating point, etc, etc..

running an engine cooler than oem specs is definetly not good for it.

You run it at lower temp when you do endurance racings, or the like.

then why are there many 68 deg -160 deg thermo's/

Low temp. thermostats open up earlier than OEM ones, that allows coolents to flow through earlier and keeps the engine at a cooler operating temp.

That's how I understand it. If I am wrong, feel free to flame me.

I run a 160deg thermo, and the car runs like stock. I was overheating when I added turbo and left stock thermo.

Thats exactly right.