My 1966 cutlass with a mild build 350 will run hot in traffic,will a 6 blade fan and 160 degree thermostat help,new 3 core aluminum radiator but no schroud,4 blade fan on it now.

 

You need a shroud, the correct fan, the correct fan penetration into the shroud and the seals to prevent air bypass.

 

It would help if you defined “run hot” with actual temperatures at extended idle and cruising at highway speeds.

 

x2

She's not going to run right without a shroud.

 

It didn’t come with a shroud from the factory.

 

Back to back successive posts from the bosses, love it.

GKranig1 I had a stock 67 Cutlass 330, and she came 2 row, 4 blade, and no shroud. And she ran warm to hot in bad traffic.

As members have said, shroud is the key here. I can't imagine a larger performance modified engine being happy with the baseline factory setup.

I will just let Hot Rod lay it out. As the paragraph is short and succinct.

"The circular area of even a large fan is significantly smaller than the rectangular surface area of the radiator. That means that, by itself, the fan will cover only a portion of the radiator, possibly as little as 50 percent. That's a lot of air that is not being pulled through the radiator. In addition, a lot of air will be drawn from around the radiator, as it follows the path of least resistance. The solution is a fan shroud. Shrouds block out any air that isn't drawn through the radiator, and create a vacuum to expand the fan's ability pull from the entire surface area of the radiator." https://www.hotrod.com/articles/building-a-fan-shroud

As you can see this move is a no-brainer.

 

I run a single 1.25" row cheapy (well not so cheap today)aluminum radiator with plastic tanks, 18" flex fan 1inch from the radiator, 180* thermostat, and no shroud on my 67.

 

Like they said, a shroud with your 6 blade clutch fan should help. Make sure all the flaps around the radiator are in place. Also overdrive pulleys, like the factory A/C pullies, closed impeller water pump and high flow Robert Shaw thermostat in 160 all add up. My 9 to 1 350 never got above 190 with a 2 core, no shroud and a 4 blade fan. But in wall to wall, hot and humid traffic, I bet it would go another 20 degrees. My current 9.5 to 1 350 takes a while to get up to temperature all of the extras I mentioned plus a big aluminum 2 core with Dodge Stratus electric fans.

 

A little time searching here and on the Googler, 9 of 10x the Googler brings you right back here. We have ~ 10,000 threads here addressing cooling system problems.
Define hot? 200-220° is normal.
Where do you live?

The wrong liquid and or air flow are generally the top two root causes of heat not being properly rejected. Third is an inaccurate temperature measuring device.

No shroud and the wrong fan could be a direction I go in.
Eliminate the basics.... the gauge accuracy, fan deviation from OEM, fan proximity (distance) to the radiator core...belt tension... correct stat... correct pulleys...collapsed lower hose...coolant mix & level....cap, et al...

A 160° stat can cause hot versus a 190° stat. Do some homework on this cuz Im not here to lock horns with the 160 people.

We need an updated block of sticky threads, this being at the top of the heap, along with timing, carbs, ignition, rear ends et al....and of course, addressing the header application listings for the infamous Supreme engine/frame offset....Though that one could have finally died a slow death???

 

Use a Hayden 2705 fan clutch and a fan that is a good fit for your shroud. You may need to get a new water pump if the neck length for your current pump does not yield the correct fan penetration into the shroud.

 

I'm not sure what all this shroud talk on here is.............The shroud for a 66 isn't much of a shroud at all, and the fan sits very close to the radiator already. I wouldn't waste any energy on a shroud for a 66.

If it heats up sitting or in slow traffic you need more fan.
If it heats up while driving you have a flow problem:
1. Water flow- hardly ever the case but....do you have the right pump and impeller? Is the stat working? Do you have crud in your block?
2. Air flow - is your radiator big enough? Do you have the rubber air dams installed around the radiator correctly? Is your fan, or fan clutch working properly?

The six blade 18" fan with a standard duty clutch and 160 stat should cool it plenty, however, those factory four blade 19's are pretty good.

My personal preference is the Cold Case unit with Spal fans and the Fast Monty shroud. Works flawlessly on even the rowdy girls.