What temperature Is your GTO running??
 

I have 1966 GTO Tri-power, 4-speed. It runs around 190-200 degrees. Yesterday I was Driving it to my favorite Cruising place. It is about 40 minutes away hitting regular stop lights. The temperature outside was around 85 degrees at 5:30pm.
The engine temperature was around 200-205 with all the stop lights.
Taking to a guy at the show who was an old engine builder said that was to hot for the engine.

I have a stock radiator and fan. Use regular coolant with a bottle of wetter water. (or something similar)

Questions:

Is this too hot?

If it is, what can I do to reduce the temperature?

What temp does your GTO run on the road?

Thanks,
FB66

If it doesn't boil over and stays there you're fine. If it creeps higher than that I'd start being concerned. I like mine to run around 185.

Double check your gauge
 

I thought my identical setup as you have was doing the same. had an after market gauge under the dash. Went back to factory gauge calibrated by Peter S.
Seemed to run cooler, Double checked with infer red sensor. Happy with results. Good Luck

Good point. Always a good idea to verify your gauge.

For non-computer cars I use a 160F thermostat and rad/fan/shroud for an AC car.

Tow car used to be the 72 wagon and pulled Monteagle on a July noon and never broke 200F. Usually runs under 180F even at light (but can really hear fan whine). Do not drive slow.

Rig that day was as shown:
http://performanceresearch.us/padgett/cars/rig3.jpg

Great point.
I have never checked the gauges for accuracy.

Even GM says in the Service Manual: if in doubt use a mechanical gauge. Factory instrument senders are notorious for inaccuracy and failing.

I have several TSBs warning of faulty oil pressure senders in particular. Back in the day I used to keep a couple of senders on the shelf just for when not if.

Also none of the senders are one-size-fits-all, are many different gauges and gauge/switch combos just in A-bodies.

ps when in doubt check. It is possible to "fix" a dash gauge to read anything desired.

How do you check the gauges?
Never done this before.
FB66

I would use an infrared temp gun aimed at the water neck. But check a few places. Preferably bare metal as surface reflectivity can affect readings. But it should read close enough to give you an idea of what's really going on.

It may seem hot but it is not really. With a pressure cap and 50/50 mix of antifreeze it is not going to boil until over 260 degrees. These older engines can withstand higher temperatures without damage than new thin walled ones.

On mine, 571 cu in Pontiac I run a cold case aluminum radiator with a stock shroud with a large HD clutch fan, in Az. 100 deg. heat driving around town 40 to 50 stays 170 172, on the highway around 65 for a period of time 185 . I do run a 160 thermostat. I did try the (2) electric fan setup, did not work ran hot, hard to beat the stock shroud and clutch fan.

Did the exact same thing.

Does anyone run evens coolant?

https://www.evanscoolant.com/

Expensive. In my opinion, it basically raises the boiling point versus 50/50 anti-freeze. It has some properties that say prevents cohesion of water to the internal engine parts to prevent hot spots/steam pockets.

If you develop a leak out on the road - your not going to most auto stores to get it.

Water Wetter will work in the same way with regards to the cohesion claim. I used it and it dropped my engine temps just slightly.

I went with a good flex fan that added some good cooling at the lower speeds. Only problem is that it has a noticeable "whirring" sound that some do not like. Not an issue for me. So that would be my recommendation as to where to look next. If you have a fan shroud, and you should have one, just make sure the aftermarket fan diameter will work within the shroud.

You also want to check timing, vacuum advance to make sure it is operating (helps to cool the engine temps down) and possibly a lean carb condition which will throw more heat into the cylinders.

Try raising your idle RPM's with the gas pedal in stop/go traffic since it's a 4-speed. Higher RPM's will draw more air through the radiator. I do this sometimes with my '73 Fury and AC/automatic - put it in neutral and raise the RPM's to help cool in stop/go traffic which is also cited/recommended in the owners manual.

The bottom line is that trying to "band-aide" a hot running engine is just that, a band-aide. Get it working right in the first place and you won't need the band-aides.

200-205 degrees IS too hot for these engines unless it is due to stop/go traffic and as soon as you are rolling it drops right down - which I believe you experienced.

With an overheating problem the first and about the easiest thing to start with is replacing the fan clutch, and as long as your are at it I prefer the Hayden 2797 severe duty. I've run this clutch on all sorts of Pontiacs and on stock fans from 18" to 19.5" with great results. When it engages on a hot day it does make some noise, but if you remember that it is pulling massive amounts of air through the radiator it gets much easier to put up with. Also like any thermal fan, it ramps up through the engagement process and only sounds like a helicopter landing on your roof when it is fully engaged doing its job.

Can you use the clutch fan with the stock water pump and shroud?
Are the fans separate from the clutch?
Do I need to order a 19.5" fan also?

Thanks
FB66

You can change out the fan clutch and nothing more and continue to run the current stock fan. It will be better if the smaller fan on the engine now is a seven blade unit. The new clutch is thicker but the location of the mounting flanges keep the fan the same distance front to rear.

My '67 cooling system was in good shape and was set up as delivered without AC. That meant it had the short 15.5" tall core, smaller 7" pulley on crank and larger 8" pulley on water pump along with the original H.O. 7 blade fan. It ran basically at thermostat all the time with no air. After I installed the Vintage Air unit the temps would creep up slightly while driving so I added the 2797 clutch and that solved the running problem but temps would still climb up to 190-195 if stuck in traffic on a 100+ degree day with the air conditioning blasting.. Next thing I did was change to the AC pulleys with an 8" on the crank and 7" on the water pump which went from an under driven pump and fan to an over driven setup. Still had the small fan but even with the AC on it never got over 190° in stop and go traffic. Went three summers with good results, but finally made the change to the deeper 17.5" AC radiator support and a Cold Case radiator along with going to the 19.5" fan and new shroud. Now it runs at thermostat regardless of how hot the day is or if I'm stuck in bumper to bumper traffic. Anyway, best to start with a new fan clutch and proceed from there if needed.

Why is this fan clutch better? Is it because it spins faster?
I do not have A/C. This has been a huge help. Thanks to all the guys who replied.
Cross my fingers.
Thanks
FB66

My engine.
Stock shroud and 18" fan

Another vote for a clutch fan and stock shroud. I'm running 180s in the summer here