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Old 03-13-2009, 11:41 AM
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Importance of a shroud with electric fans

I've been working on a 1970 Dodge Charger thats been plagued with cooling problems and I just cant seem to get a handle on it. It has an iron head, stroked 400 in it now. At idle, when the ambient temp is above 80 degrees, it quickly reaches 260+. To try to help correct the problem, a dual core aluminum radiator and dual electric fans have been installed on the back of the radiator. The radiator has no shroud on the back side and no splash shield at the bottom of the engine bay.

Would adding a fan shroud and a splash shield lower or raise the temp with the electric fans installed? The car has no fan attatched to the water pump. Additionally, the car has had quite a few electrical issues. Could a lack of voltage to the fans be an aggravating factor? They seem to turn fine but I have no way of checking to see what the actual speed of them is.

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Old 03-13-2009, 12:34 PM
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Quote:
Originally Posted by DaSouthWon
I've been working on a 1970 Dodge Charger thats been plagued with cooling problems and I just cant seem to get a handle on it. It has an iron head, stroked 400 in it now. At idle, when the ambient temp is above 80 degrees, it quickly reaches 260+. To try to help correct the problem, a dual core aluminum radiator and dual electric fans have been installed on the back of the radiator. The radiator has no shroud on the back side and no splash shield at the bottom of the engine bay.

Would adding a fan shroud and a splash shield lower or raise the temp with the electric fans installed? The car has no fan attatched to the water pump. Additionally, the car has had quite a few electrical issues. Could a lack of voltage to the fans be an aggravating factor? They seem to turn fine but I have no way of checking to see what the actual speed of them is.
The splash shield is intended to direct air thru the radiator not keep water out of the engine room, it should be there.

A dual core aluminum radiator may not be sufficient, I run into this a lot in-spite of the great advertising claims for aluminum radiators. They are quite persnickety about air flow probably because of their inherently less effective rate of heat transfer.

You problem, however, is quite common to insufficient air flow. This is also a common ailment of electric fans. A radiator needs a shroud and the shroud needs some length between it and the fan. The shroud needs to envelop the perimeter of the radiator core such that a fan pulling air will cause a low pressure area to form over the entire core area. Without this configuration it is difficult if not impossible to pull air thru all of the core. With electric fans it is difficult to achieve this as they tend to mount intimately close to the radiator so even with what they are pleased to call a shroud they are only pulling, or pushing if in front, air that is no more than the diameter of the fan.

Purveyors of electric fans like to sell you with big CFM numbers. What it is about Hot Rodders I don't know, they think because they're seeing big numbers that this stuff is better. Like high flow thermostats or water pumps, what actually defines high flow? And the purpose of a thermostat is to restrict and control a flow in order to maintain a desired temperature. Ok enough soap box! I don't think dual fans are the electric fan solution because too much core is not exposed to air flow and that typical electric fan installations are too close to the radiator for any effective function of the type shroud they come with. A four fan solution with smaller fans facing more area would be a better solution, but nobody makes such a configuration.

Potential Solutions:
- The simple solution is to go back to the factory water pump driven fan with a factory shroud.

- Another would be to leave the fans where they are and remove any intimate shrouding they currently have. Then install a shroud similar in shape and size to the OEM unit. The fans operating in such a shroud would create a jet of exhaust air at the mouth of the shroud which would reduce air pressure inside the shroud and a flow would develop over the core area not directly in front of the fans.

- Third option could be a single electric fan mounted to the mouth of an OEM shroud such that it would pull air over the core area similar to how the water pump mounted fan does.

Bogie
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Old 03-13-2009, 12:40 PM
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The only thing worse than cooling problems is electrical problems for me. Sometimes it's difficult to chase down the culprit when a motor is overheating, but if you go one by one on a checklist, you can usually find the error of your ways. I'd start by engaging the fans and holding a sheet of newspaper in front of the radiator. Will the fans suck the paper up against the radiator and hold it there? If not, then you've found at least one problem with the system. Here's a pretty good tutorial from the wiki that you can use as a checklist....
http://www.crankshaftcoalition.com/w...cooling_system
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