The best way to maximize airflow through the radiator with an engine-driven fan is to use
Dave Visaggi; Scarsdale, NY: I have a '67 Pontiac LeMans with a Chevy 330hp 350ci crate engine. It has Vortec heads and a Holley 650 vacuum-secondary carb. It also has a serpentine beltdrive, which turns a reverse-spin water pump meant for '84 to '91 Corvettes. The car has an OEM-style radiator with top and bottom tanks. It also has aftermarket A/C installed. It's a daily driver, and I am struggling with a cooling system problem.
My car runs hot in traffic on 95-degree days. I would prefer to cool it with only a radiator, a beltdriven fan, and a shroud. I like to avoid electrical parts because when they quit, there is usually no warning. I would also like to avoid cutting up things to install a big radiator. Is there any way to size a radiator to the cooling load to avoid trial and error? I would like to stick the next size radiator in the car but would hate to waste the money if I then find I have to go bigger and start cutting. Also, what is the appropriate thermostat for that engine? I currently have a 180. I would prefer a 195 because the car is just a bit stinky at idle, and that appears to go away when it is running hot. My '97 Suburban ran all day long at 210, and I figure my combustion efficiency and thus fuel economy and power would improve with higher water temp. This is all about enjoying the car from behind the windshield.
Jeff Smith: Dave, let's see if we can help make your car more fun to drive. To start with, it appears the stock vertical flow radiator for a '67 Tempest is 155/8 inches tall and 243/4 inches wide. This should be more than sufficient for a small-block Chevy (assuming it's in good condition), so a larger radiator probably isn't necessary. I noticed a couple of clues in your description. First, your car suffers from the classic low-speed overheating problem. You don't say exactly how hot the engine gets, but from the description of your Suburban running at 210 degrees F, I'll assume this is not "hot," which is good. Next, you say you are running a serpentine beltdrive package using a reverse-rotation water pump. It also sounds like you are currently using an engine-driven mechanical fan. My guess is that the engine-driven fan you are using is likely intended for the more common V-belt accessory drive systems. This works very well as long as the fan is spinning in the proper direction. However, your reverse-rotation water pump spins in the opposite direction. Spinning a normal-direction fan backward will still move air, but the efficiency is greatly reduced. What you need is a reverse-direction fan.
Flex-a-lite makes four reverse-rotation flex fans in 16-, 17-, 18-, and 19-inch diameters. With the stock-width radiator for a '67 Pontiac, you can easily stuff in an 18-inch-diameter fan (PN 1518, $53.95, SummitRacing.com), but you will need a good shroud to make it work really well. A larger-diameter fan pulls more air because the blade tip speed is faster for any given engine speed. This higher tip speed will generate a greater pressure drop behind the radiator. Virtually as critical as the fan is a properly designed shroud. The shroud's purpose is to pull air through the entire surface of the radiator core. Make sure the fan is never closer than 1 inch from the face of the radiator, and you should also have at least 1/2 inch between the trailing edge of the fan tips and the accessory drive. You can also increase airflow through the radiator by sealing all the areas ahead of the radiator core support. This will force all the air entering the grille to travel through the radiator rather than around it.
If your radiator is marginal, you have a choice between aluminum and brass/copper. Aluminum is lighter, generally offers a larger capacity, and will do an excellent job of cooling. If you're on a budget, look for a brass/copper unit with a high-density core. The one company we know of that sells these is U.S. Radiator. Less expensive brass/copper radiators are often fitted with low-density cores. To compare them, measure the space between the coolant tubes. High-density cores will feature less distance between the tubes because there are more tubes within a given core size. Then you can run a 195-degree thermostat that will maintain that higher temperature. Remember that a thermostat's only job is to maintain minimum engine temperature. Frankly, if the engine is stinky at lower engine temperatures, very little will change when it completely warms up (unless we're dealing with an electric choke that's set too rich). I would suggest addressing the problem with a careful adjustment of the idle-mixture screws at the lean limit along with checking the initial timing. Run a minimum of 10 degrees initial timing, and if the engine doesn't rattle on hard acceleration, bump that up to around 12 to 14 degrees initial with a total of around 36 degrees mechanical advance. These changes and a functioning vacuum-advance curve will really help move you toward your goal of a cool-running vehicle that gets decent mileage. And that will be much more fun to drive.
Mark 7 Radiators
Bay City, MI