Thread: Cold thermostat causing rich condition?

Hey guys...
So I have a general technical question.
I read somewhere online, possibly here, that a lower temp thermostat will cause a car to run rich due to the car staying in warm up mode. Is there any truth to this statement?
The reason I ask is that the '96 GPSE 3.1 I have been working on was running really rich when I got it. I had everything apart over the course of about a week while I was repairing the rear exhaust manifold and during the process I replaced the thermostat with one rated at 195 deg. and after putting it all back together the car is no longer running rich, and the P0420 trouble code that was making me think I needed a new catalytic converter has cleared itself and has stayed off for almost 80 miles of driving. I think the old thermostat was a 160 deg. part and I'm really wondering if that was the root of the whole issue with this car.
So at this point, I'm just trying to understand the technicalities a little more and I figure one of the brilliant minds here can shed some light on the subject. I'm sorry if this is a redundant topic, I couldn't find the original post I had been reading.

Thanks,
Tim


Sent from my Windows Phone.

A 160* thermostat keeps the car too cold so that it never enters "closed loop" where the computer actually starts watching the O2 sensor to determine A/F ratio. Typically, most manufacturer's set "closed loop" at around 176-178*F.

Thanks for the replies guys.
FFDP - The rear manifold issue was that I sheared a bolt in the flange when I removed the cat to inspect it, just had to extract the bolt, I don't think anything with the mani was causing an issue as far as trouble codes go.
Sven - Thanks for the technical answer, that is basically what I had read just wanted to be sure I wasn't confusing myself with something else I had read. The way my mind works, I like to know as many technical details of how things work and why, really helps with troubleshooting.
I've always been a guy that does my own work on my cars, and lately I've realized that my fundamental knowledge of how things work together is limited and I've been trying to learn a lot of the technicalities which is what leads me to these automotive forums.

Thanks Again,
Tim