I have about 400 miles on a rebuilt 66 396/325, all stock with a very mild cam. I have a new 4 core radiator with shroud, a 180 deg thermostat, and a standard duty fan clutch with a GM 6 blade fan. I have an ac condenser installed, but have not yet charged the ac system with freon. The car runs right at 180 on the road even in 90+ weather all day long, but at idle at a stop light, it creeps up to about 195-200. After sitting at a stoplight, as soon as I start driving (even at 45 mph) the engine returns to 180.

I am thinking that when I charge and run the ac system, the engine will run hotter due to the hot condenser in front of the radiator.

Could anyone give me a range of water temperatures that would be considered 1) safe or normal, 2) hot but OK, and 3) overheated - shut it down?

I did a search, but there seems to be varied opinions on this. I thought I could collect the numbers here is one place. Thanks, Wayne

The key for me is the pressure cap. A 15 lb cap (usually on A/C cars) raises the boiling point of water by about 45 degrees F. So ...

1. "Normal" is the thermostat temperature.

2. "Hot but OK" is *Not Boiling* ... perhaps as high as 212 + 45 = 257 F.

3. "Overheated, shut it down" Boiling ... pressure cap venting.

The numbers you cite are very good! I'm running a Power Glide, I put it in neutral at stops when the A/C is running. The faster idle moves more air.

Notes about Anti-freeze. It reduces the ability of the coolant to transfer heat. It's name is it's purpose, it really doesn't help the boiling point very much. Use as little as possible, just enough to match your winter conditions. Don't run plain water, the A-F protects against corrosion in the radiator. CHANGE YOUR COOLANT ... I do it after about two years.

My 59 will run right at 180 on the hiway--even here in So Texas.
I have twin electric fans that don't even kick on 'till 225*.

Personally---I like it running close to 200 most of the time, I do not think 180 is warm enough

My BB runs a steady 180*, bt I have a truck. Alot more grill space. I have a 4 core with a flex fan (for now, I am installing a dual electric fan as we speak). When I was trying to fix a belt throwing issue, I went to the factory water pump pulley and she creeped up to 200-210 at a red light. Went back to the after market chrome one and she went back to a steady 180*. Try a different pulley.

I think what you described 195-200 is fine, but if you are like me I want her at a steady 180. I think you are fine. Also, where to you have your sending unit. I have one in the intake and one in the head. The head temp is usally about 10-15 degrees hotter than the intake.

A couple things that could explain the difference between low speed and higer speed temps are timing and the shroud. Typically, at lower rpm you will have less timing and it increases with rpm, making the engine run cooler. The shroud and the position of the fan blades in relation to it won't make much, if any, difference at speed but can make a big difference in traffic conditions. If the fan blades are too far in or out of the shroud you could see much higher temps until airflow from speed is adequate.

New Corvettes...the fans don't even come on until the coolant temp reaches 225.
Where is the sending unit installed? Vacuum advance hooked up to a ported source?

As a rule, I try to keep a BB to no higher than 210`, preferable is around 180-190. I'd shut it down at 240`.

I'd agree, try advancing your base timing a hair, make sure your shroud is in good condition and a tight fit to both radiator & fan.

if your vacuum advance is hooked to a ported source, try hooking it to manifold vacuum so it's advanced at idle.
you will probably have to turn the idle speed down a little bit.

I am running manifold vacuum and 50/50 water/antifreeze. It has been while since I timed the engine, but I recall my base timing was at 17 and it was all in at 34 at about 2900 rpm. The engine never pings, but I have not run it very hard through the gears so far (only a couple of times shifting at 4000 rpm). The engine ran right at 190 on the highway for the first 100 miles or so after break in and has gradually come down to 180 on the highway over the second 100 miles and stays there now. The fan blades are about 1/2 in and 1/2 out of the shroud at the top and the rear edge of the fan blades are even with the shroud edge at the bottom.

Last year, I searched for a heavy duty fan clutch, but Hayden only makes one for a long water pump, and only makes the standard duty for the short water pump, so that is what I have. Could it be that the standard duty fan clutch has too much slippage when engaged to pull enough air through the condenser and radiator at idle? Thanks, Wayne

I have a 468 in my driver, Its a 70 Sta. Wgn. P.S. & A/C. I bought a fan clutch for a mid 80s 3/4 ton Suburban with dual A/Cs from a Chevy dealership, It fits inside the stock 772 fan blade and has a lot of drag when the engine is cold.
Yea it makes noise, And yes the engine does not get hot with the A/C on when its hot. This is the place to get a lot of ideas and help......
Bob ACES--AACA