OK need a lil advice here, got a 92 3.9 v6 MPFI, put in the 160 thermostat, now the ecm kicks thecode for "not reaching closed loop temperature" and now it's running rich. It has proper reading from O2, TPS and all... So do I HAVE to buy a chip to be able to run the cold thermostat?! Or is there a way to tell the ECM that 160 degreesis ok??? Whats really blowin my mind is the 160 therm. is listed as an OE optional part. So according to advance auto, you can just drop that thromo in and run it fine...

 

Mine does the same thing and i have the chip, it does not pull a CEL so i have not worried about it, People say not to run the 160 because it wont go to closed loop, but because it does not go to close loop it is pumping more gas in it. It did not hurt my milage too bad either, and jet recommends running the 160 with a stage 2.

 

well after researching the percentage of each sensors responsibility for the fuel/air mix, and some basic math... I've got the O2 unplugged and it smells closer to 14.7:1 than it was.

And ALL of that nasty exhaust gurgle on the rev drop is GONE! Now it'll wind to 3500 and come down smooth as ice, so i'm about to put approx 1,500 miles on it from now till monday and i'll come back n tell ya how it did...

 

cool deal

 

a 160 thermostat is a stupid mod to do. all it does is trick the computer into thinking that the engine isnt warmed up, so it pumps more gas into the engine. you're also shortening the life of the motor by letting it run cold all the time. the optimal temp for a 3.9 magnum is between 185 and 190. stock is 195. a 180 thermo is a much better choice if you really think you have to waste money trying to get a half a horsepower.

 

Well i have had a 195, 180, and 160 in mine and it ran best with the 160, so i kept it in there.

 

Not to mention that once you begin to change intakes, open exhaust, and adding performance modules the "factory" specs can go out the window, Jet, Hypertech, and Venom all suggest running cooler thermostats, and specifically the 3.9 MPFI is suggested to run the 160 for best performance from the chip.A cooler engine, and thus cooler intake manifold, allows for a cooler denser air charge, cooler oil is less prone to thermal breakdown. And since when does LOWering the amount of expansion and contraction that the metal parts ofyour enginego through by lowering the heat rangethey go through a bad thing?However it is a bad ida to run NO thermostat because you'll get a nice low temp reading but the water isn't staying in the engine long enough to absorb enough heat energy, nor in the radiator long enough to dissipate said heat.

 

expansion isnt the issue with the 3.9. you're not going to break a motor with basically all cast iron components just by running a normal temp. now a newer engine with aluminum heads, i can see your point. the point is, a hotter engine runs cleaner. running an engine cold constantly is asking for excessive carbon build up. its your truck though, do what you want.