For years we’ve been saying that there are times when tech questions seem to come in clumps—this is one of those times. Recently we’ve received quite a few letters dealing with cooling issues. Several dealt with pusher fans and slow speed overheating issues, and a similar number had questions about on and off set points for electric fan switches. We selected the following letters as they best represented those questions—they have been edited for length.
One Hot Pickup
I’m having an overheating problem with my 1957 Cameo pickup. It has a big-block Chevy with an 8-71 Weiand blower, a universal-type aluminum radiator, 180-degree thermostat, and dual 11-inch pusher fans thatare thermostatically controlled. There’s approximately 1/2 inch between the back of the radiator and blower pulleys. The fans are Flex-a-lite 330 (25.5x12.375 inch with a shroud), which is against the front of the radiator. Does the shroud block airflow? The fans are rated at 2,029 cfm. Do you think more cfm will work, like the Flex-a-lite 180, 16-inch, 3,300 cfm?
At 35 mph temperature is fine, but it will rise soon as the truck stopped. I’ve considered many things and believe I have a solution. Remove the existing fans and fan shroud blockage. I calculated the actual dual 11-inch-diameter square inch minus the square inch of the motors and came up with 170 square inches. The radiator is approximately 390 square inches. That leaves 220 square inches that are blocked. If the fans could be mounted as pullers, it would probably work, but, no room. So my idea is to use an un-shrouded 16-inch pusher fan. I believe un-shrouding the radiator will allow it to work at speed, keeping it cooler so when you slow down the electric fan will have less work to keep it cool at idle. I have the adjustable thermostatic controller.
Any thoughts? Thanks.
Via the Internet
A We felt there were a number of issues here. First and foremost, when doing any engine swap, start with the radiator first, allow enough room for a fan, and then put the engine where it needs to be. In cases like this the ideal fix would be to move the radiator forward or the engine back to get the needed space, but in the real world with a car, or this case a truck that’s already finished those modifications may not be viable options. So, the only other choice is to put an electric fan, or fans, in front of the radiator. Electric fans work better as pullers than pushers, but again, the options here are limited. The cure you suggest just might work, however, the Flex-a-lite 180 is a puller fan with a shroud so it’s not suited to your application. Also, be wary of fan ratings when comparing one make to another. Various testing procedures are used so cfm ratings should only be used to compare fans from the same company.
To get a fan manufacturer’s opinion, we sent Bob’s letter to our friends at Flex-a-lite, this is what they had to say:
“This is nothing more than an air supply problem. The blockage concern may hold true with your truck, when you take into account the shrouding and the radiator that’s hidden behind the core support, even the grille may play a part in this. A 16-inch fan with a true 3,000 cfm may be hard to come by. Our 398 (Flex-a-lite’s reversible Syclone S-Blade electric fan) and the 119 (Flex-a-lite’s LoBoy auxiliary pusher electric fan) are rated at 2,500 cfm and are 16 inches in diameter.” —David Heutmaker, Flex-a-lite
I restored/rebuilt my 1934 Dodge pickup for the last time last year. The engine is a 327 SBC with flat-top pistons, a 350hp/350ci cam, 2.02/1.60 heads, an Edelbrock EPS Performer manifold with a 570-cfm Holley, Sanderson QP-1000 ceramic-coated headers, 2-1/2 inch exhaust pipes, and ACCEL HEI. I have a Walker radiator.
The cooling system worked very well. Rarely did the temp rise above 160 degrees unless I was in stop-and-go traffic, then it might rise to about 180 degrees but then I had a cooling problem at Hot August Nights last year. With the constant sitting in traffic during the parades and very little movement, the temperature gauge rose to 240 degrees and above. I was constantly putting the AT in neutral and raising the rpm in an attempt to get the temp down.
I decided to change the system and go to an electric fan. I’ve been told to install a 180-degree high-flow thermostat with a 205-on/195-off temperature sensor; other sources say a carbureted engine should use a 160-degree thermostat with a 176-on/161-off sensor and a fuel-injected engine should use a 180 thermostat with a 200-on/185-off sensor. I can find sensors that are 185 degrees–on/165-off and 195-on/175-off, but it doesn’t say which thermostat to use. Another catalog lists sensors that are 185 degrees–on/170-off for a 180-degree thermostat and 200 degrees–on/185-off for a 195-degree thermostat.
Can you shed any light on my problem? Thanks.
If a street rod is equipped with a late-model, computer-controlled, fuel-injected engine, trying to run it too cold creates more ...
A Let’s start with engine-operating temperature first. Most engines today are designed to operate within a “normal” temperature range of 195 to 220 degrees. Of course one of the reasons for that can be traced to emission control regulations and equipment. But thanks to vastly improved lubricants and engine components these increased operating temperatures aren’t an issue.
If a street rod is equipped with a late-model, computer-controlled, fuel-injected engine, trying to run it too cold creates more problems than it cures—keep the engine in the 195-degree and slightly above range. On the other hand, older, carbureted engines can run a little cooler, with 180 degrees the goal.
As for thermostats, using one that opens at 160 degrees is thought by some to prevent overheating because it provides a temperature “buffer” of sorts—but it doesn’t, it just provides a lower starting point. If an engine is going to go to 240 degrees for whatever reason, it’s going to get that hot regardless of the thermostat. Thermostats establish minimum operating temperature, and unless one sticks closed or is for some reason more restrictive than normal, maximum water temperature is dependent on the remainder of the cooling system. When compared to a 160-degree thermostat, a 180 will provide cleaner combustion, warm the oil to the point that contaminates will “boil off” and in general performance will be improved. We always recommend the use of a high-flow thermostat that can be ordered from a number of our advertisers.
Another factor to consider is coolant. A 50/50 mixture of water and ethylene glycol antifreeze in the cooling system will boil at 225 degrees if the cap is open. But as long as the system is sealed and holds pressure, a radiator cap rated at 15 psi will increase the boiling temperature of a 50/50 coolant blend up to 265 degrees F. That’s not to say you want an engine to run that hot, but preventing the cooling system from losing fluid is essential to maintain the proper level.
As for electric fan controls the hot ticket (no pun intended) is for the “off” temperature to be slightly higher than the thermostat. Any lower than that and the thermostat may cycle open and closed and engine temperature will not stabilize, which presents its own set of problems. The “on” temperature of the switch is usually around 12 to 15 degrees above the “off” temperature.
Of course another option is one of the adjustable fan switches on the market; they allow you to tailor the set points for your particular application and maybe even more importantly, allow changes to be made easily whenever necessary.