ok, been exploring the overheating again, I currently running 350 engine, rebuilt, new 3 core rad, new water pump, just installed filler plates on top between core support and grill, was using stock (new) fan clutch, with bigger fan, and now trying a plastic HP fan, not working so well, driving my temps stay around 180, stop light to stop light, or parked temp start rising up past 200, with original fan clutch i raise the rpms up and the temps start to drop. I was reading in here that maybe I need to scrap the headers and go to HP manifolds, anyone done this? and I was looking into changing the shroud, mine is 6" deep and I seen a 9" deep one for 400 models, that would eliminate the use of a spacer on fan.

was looking on year one parts, has anyone tried header blankets?

Headers can be coated both inside and out. I had to have mine redone after breaking in the engine with the headers on (specifically listed as a no-no in the Doug's Headers info) and marred the coating a bit. So a local shop recoated mine inside and out with ceramics.

I have no interior in my car (waiting on paint) and with only a carpet protector between my shoes and the bare floor pan, I feel very little heat coming through from the headers directly below.

I think you are on the right track from the rest of your situation. Go back to the OEM HD fan and clutch and perhaps get the deeper fan shroud. Your driving temps are great for an FGF.

what temp is the t-stat?

"up past 200" How much past 200?

210 then levels off? 220 then levels off? These are not an overheat situation. Normal. These cars came stock with 190 t-stat, so Pontiac didn't even expect them to start cooling themselves off until just BARELY cracking the t-stat at 190 degrees. And a good 190 t-stat will crack open at 187 to 193, and will not fully open until 222 degrees (incidentally this is a direct quote taken from page 6A-3 of the 1968 Pontiac service manual).

So 222 degrees is how hot coolant needs to reach in order to allow full flow and max engine cooling. Pontiac expects this and the engines are designed to take it, plus several more degrees, with no problem.

Pontiac designed these engines to run all day long cycling back and forth anywhere between 190 and maybe 220/225 coolant temp. Why people seem to want to keep driving this number range lower has always confused me...

But if you're seeing it continue to rise to 230, 240 or higher? Yes indeed you have a problem.

If so, clear photos of your current shroud and fan setup might help a bunch.

Did you set tight clearance between your water pump vanes and divider plate?

What year is this car? 8 bolt or 11 bolt water pump?

If it maintains 180 while driving then that tells me water pump and radiator are probably fine. So I'd bet dollars to donuts you have nothing but a fan/shroud issue, or if your temps are never exceeding 225, you don't even have a problem at all and it's working exactly as designed...

I believe I am using a 180 t-stat. 1968 firebird, I installed new divider plates in with new water pump, seemed tight, will have to figure out how to put pics on. I do have some gapage around the shroud..

Beardog, after Craze's discussion, you were supposed to say you would quit worring about being a little over 200F. Stop worrying or unplug your temp gauge. The factory idiot light supposedly doesn't come on till 250F. Most of our cars run at least 210F in traffic.

My car is boiled over at 240. Has happened a few times so I know how hot it can get before it's gonna puke. I get nervous at 210 and start looking for somewhere to go and cool off. As long as it doesn't pass 220 I feel I'm ok but if it goes past there it usually means something is wrong and it aint gonna stop climbing, on my car anyways. It's a short trip from 225 to puking on the street for mine.

I have never really had overheating issues thank god but wonder if a infared thermometer would be helpful? Take a reading of both the incoming and outgoing radiator hose to measure the temperature difference.

The question after you gather that data would be what does it mean.

OK, so I get a little nervous, I guess I shouldn't have installed a temp gauge and relied on the idiot light.. but I like gauges. I never had really gave it a chance to see if gauge levels out.. will still replace the shroud, don't like the fit. and put the clutch fan back on.
thanks guys.

i learned to turn the heater on in the car wide open,on my first car, during those times of crisis. it would halt the rise for a short time. but made it rough on the inside,at least till you got moving again.

Like crazecar said it's normal to run around 210 in traffic, as long as it isn't going to 250 or 260.
Is your fan at about the half in and half out of the shroud?