I have a 69 RS Camaro 350/350turbo w/3.73 gears and it is running about 200degrees at highway speeds. The longer I drive the car the hotter it gets. It has ran as high 220. I would prefer it to run under 200 on the road, since if it sets at light or in traffic it raises about 10-20 degrees.

First got the car about a year ago and it ran about 180 as far as I can remember. I noticed the high temp. after I installed a trans. cooler on the front of the radiator. First I ordered a new Stewart high flow water pump and 180 Thermo w/all new hoses thinking this would cure the problem. It didn't. Next added a fan spacer to the clutch fan to get it closer to the radiator. Didn't work. Next changed to a flex fan and 2" spacer. Didn't work. Next added a 16" Electric fan with thermostat on/off kit. Didn't work with or without the factory shroud. Added a pink liquid called "Water Wetter". Didn't work. Removed the trans. cooler thinking this was the problem all along and temp stayed just as high. Removed the radiator and took to shop to check it out and was told it was a newer one by the looks of the inside(thought it was new but wanted to cover all options). Changed the thermo back to a 160 with big opening and still nothing. Have even tried to drive with the rad. cap loose and still didn't work. Also have went the timing route, I have replaced the timing set and set the timing by ear.

It has a Sunpro mechanical aftermarket temp. gauge and this is the last thing I know it could be. Have you ever heard of a gauge messing up and causing this problem? I am at the end of my rope and can't take much more!! I have ordered a set of Bow Tie gauges and was also wandering if the Bow Tie water temp. gauge pt# 12361402 is a mechanical gauge?
Any help would be appreciated! Thanks

Try adding a 190 Thermostat and let me explain. The water is not staying in the radiator long enough to cool. There is no diffrence in a 180 and a 150 if you motor is running hot, cause they both will stay open all the time. You need a 190 so it will open and close open and close as the engine is running. By the way Water Wetter is some good stuff, I run it in my racecar.

you did not mention replacing the sender unit in your post.....did you try this?
You also did not mention how modified or "built" your 350 is.....hence I will assume essentially stock to mildly built. Either way....That motor should not be running at 200 degrees or over at highway speed.....or even a slow cruising speed for that matter.
You say your motor was running at 180 before and just all of a sudden started running the higher temps.....sounds like a malfunction in either the sending unit/process or the gauge.
We run mostly mild big blocks and some pretty radical built 350s....w/ 160 thermostats. As long as we keep em moving....even in slow moving traffic at rod runs, we stay below 200.
I have a feeling your not as "hot" as your gauge is reading.

One more suggestion.....I assume you have already flushed the sysem sometime during all that swapping and chasing your problem. Just a thought, but maybe there is some blockage insided the motor itself.

Hope you find the prob.
Shannon