I have a 68 400 HO, 4-speed close ratio, 4:33 rear end that runs hot at higher rpms. It has the big radiator with new, correct cap, fan shoud, operational clucth fan(correct ddaimeter), and what looks like a new water pump. It'll idle all day and run normal temps. Turns high rpms at highway speeds and the temp slowly creeps to 210-215, so I push in the clutch and let it idle as I coast and the temp goes down. Last time I had to stop and idle to wait for contruction "follow-me" truck and it cooled way down even after 15 minutes of idling. Once back in motion, gets hot. I've tried every where from 180-195 thermostats to no thermostat. (just to troubleshoot) I've been told just to live with it cuz the 400 has no water jacket between the cylinders, thus gets hot at higher rpms. Dont have a tach, but I'm pretty sure with the ratios in the tranny and rear end, they are way up there at 60 mph. Also, once it's hot like that, wont crank over till it cools down some. It has never overheated since I dont let it. Dont travel more thatn 15-20 miles when I drive it. Any suggestions ya'll?

Start with an exhaustive Tech archive search here on "hot" or "overheating". A very common problem on these cars that has been discussed a lot on the board over the years. It will give you some ideas.

In your case, I'm going to say timing, running lean or your factory baffles that channel air into the radiator are missing. You are probably going to have to define what RPM range you are having the problem at.

Use this calculator to find tire size:

http://www.csgnetwork.com/tiresizescalc.html

Then use this one to determine engine rpm:

http://www.csgnetwork.com/multirpmcalc.html

Of course this is all subject to a correct speedometer reading. If you're not sure use a GPS with a speedo function to check.

That 4.33 is a pretty short gear, you may be happier with a 3.23 or 3.55, that 4.33 is a stoplight to stoplight gear.

This is by far the most discussed topic on this board. As salmon suggested, do a search and read the topics. Right off the bat I would question the reason for such low gearing. If you are looking to drive this car on the streets the first thing I would do is change the rear gears. Consider something like a 3.55 you and the car will be much happier. Unless of course this is a track car...

for being in Texas 215 is not hot....I ran my 400 for almost 10 years here (25 k miles) and running it at 205-210-215 in summers (June -Sept)it would run about 195 in the rest of the year....this is hwy speeds at 70-75-80.
this year , getting ready for the Cannonbird Run, I changed my radiator to an aluminum large 3 core and it brought it down 15-20F.

but as for "hot" 215 here in Texas isnt running hot...
test it some more, run it longer at speed see how it reacts....when I first bought mine and drove it back from Dallas on a hot August day it ran 225-235 all the way, 240 uphills. I found it was missing the X fillers, and one side missing of the lower rubber/masticated radiator fillers, plus prev owner had added a push helper fan that was blocking air. just those 3 things brought it to run better/cooler.

timing, and if it runs too lean can also bring temps up.

and running with no t-stat is not good, the t -stat needs to be in there to slow the water down ,otherwise it wont have time to cool down in the radiator....

...runs hotter at speed than at idle...

Gotta be lean as he77...airflow shouldn't be an issue at 60mph, and water flow shouldn't be an issue at 3500 or so.

A stated above, check timing, then carb, then lots of other info available.

Post photos of engine ...

4.33 is work'n engine pretty good continuosly at 70-80 mph.
Same as Bjorn, drove mine for years with a 195 stat.
RA3/th350/3.73's. Ran 210-220 all the time.
If you dont have an analzer to check air/fuel ratio, try retarding timing 4-6 degrees. See if that helps.
Or run at highway speed somewhere you can shut it off and pull over and check spark plug color.

Thanks for all the input. I did keep the 195 stat in it still. Just this evening, I drove it about 15 miles at 50-60mph got up to 215. stopped to run an errand for 10 minutes...wont turn over fast enough to start. New starter and battery by the way. Had to wait till it cooled down...cranked right up. I could try retarding the timing some but it sure takes away the oomph! I still have lots to try and read up on thanks to ya'll. I'll keep ya posted.

I'm reading and interesting book about Pontiac engines. Well, actually, the book is being read to me. One of the first things right off the batt, install the thermostat of the temp you want the car to run at. I thought that was quite simple but it goes on to talk about Pontiacs running hot and it does talk about going back to basics and what came on these cars originally basically just as my good friend and lifelong Pontiac guy always says as well...

Do you have headers by chance? if so its usually hard to re start...the solenoid gets too hot

The new design high torque mini-starters are the greatest thing for these motors since the invention of the piston.

The new starter you just ordered, if its the big OEM style, ain't gonna solve your hot start problem. You will probably need to get a heat shield for the solenoid.

Or sell the big clunkly OEM starter to a purest.

I ran a stock starter on my bird (405 RWHP)for 10 years with a stock heat sheild. I replaced it once with a $29.99 life time warranty starter from AutoZone, used it for more than 4 years and still have it to this day (currenlty not being used).

With stock everything (including longbranch manifolds) and the original starter, I've had the hot starter issue for as long as I can remember. It happens when the car sits for about 5-10 minutes after running. Sit much longer and the starter cools down sufficiently to work normally, sit less and the starter doesn't have time to get hot enough to bog down. Since the engine is warmed up, it always starts OK with even the slightest cranking but that has not taken away from the anxiety every time the starter is obviously struggling.

It happens on gas fill-ups, the quick run into a store for something, etc. I've learned to not trust shutting the car down for a freight train or long traffic backup.... just in case. Wouldn't want to wait for the thing to cool down while in the middle of the road.

If the starter is good, slow cranking when hot is a sign of timing to far advanced.
Ya, retarding it takes away low end performance. But it also increases top end.
May find a happy middle by recurving the distributor.

I've always gone with the prescribed 9 degrees BTDC.

You mention a stock heat shield. I have a solenoid shield on mine but I thought it was installed within the last few years.

It's a double-walled shield that attaches to one of the long bolts and to a bolt of the solenoid. Does that sound like a factory shield?

My guess his set up wants more then 9* initial.

I've been having issues running hot, as well, or so I thought. After I installed all the missing filler panels it still crept up to 210˚-220˚. Turns out my temperature gauge is off by 20˚.

That is why I don't have gages. It's too stressful, and I agree, they are not always the most accurate.

The heat sheild I had was the solenoid heat sheild on my car. I also ran LBS's. I guess I was lucky, I NEVER once had hot start issues. Even when my car was running hot (before installing the correct 7-blade, 19.5" clutch fan. Even though the car was running hot back then, it always started with ZERO issues...

no headers, all stock as far as I can tell except put a Holley 750 on it. I put all the panels and baffles back on it and it got hot by the time I got home. Just enough to start spitting a little out the rad overflow. BUT, it restarted just fine. wierd. I pointed my nifty temp gun at the thermo housing and it read 210. My gage must be off some. I was getting 220 on the gage. saw a post about water pump impeller clearance. might try that next.

impeller clearance gives you a little...not much enough to go from spewing to running cool though...

Dont fill radiator to top.
About an 1" down when cold.