This has me a bit concerned...so, I thought I'd ask here.

What's the average temperature for a more or less stock 3.1L at idle? 160*?

And what's the average temperature for a 3.1L under normal operation? 200-220*?

I ask because the highest temperature I can seem to get my gauge to go is 160* at idle. I've tried some light reving to help get it past that point, but it won't...

And because of that my fan never turns on...however, the upper plenum to the intake, if you hold your hand on it for a couple seconds, will burn you. Yea, that's pretty hot for an intake.

Now that I've typed this up, and laid out the facts...I'm pretty much certain that my coolant temperature sensor is shot.

 

You may also have a thermostat stuck open. When did you change it last?

Mine seemed to run around 200 all the time after it warmed up. It was a 90 firebird with a 3.1.

 

Yea I would replace the Thermostat.

While I'm driving lets say on the highway it will never go past the first line (I assume thats 160 or 180) and my fan will not kick on.

When I'm driving down the side streets it will get up to 220.

At idle it will go a bit passed 220 and the fan will kick on. I hate that so much.

 

it definately sounds like a stuck open thermostat, but, hey, man, 220 is in the best operating range for temperature. Colder is NOT better, it's most efficient at that temp. That's why the fan won't kick on until it get's hotter than that. I'd say the reason why the engine stays so cold while driving, is because with cold coolant being circulated through the engine due to a faulty stat, and it being further cooled by the air blowing through the radiator while you're driving, the coolant doesn't have a chance to warm up . You're lucky it got stuck open and not closed like always seems to happen with my parents vehicles, all in the same year they blew head gaskets because of either a bad pump or a stuck closed thermostat

 

Mine kicks on at 85* C. roughly 202*F. I just changed the t-stat, it's a pretty big job.