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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
| Posts: | 532 |
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When a car is at rest, the only way air will flow through its radiator is if it's pulled through by the engine fan. There's a lot of open space between the radiator and fan in a stock JH, and because of this, the fan is not very good at its job when the hood is up. A fan shroud -- ducting to ensure that air pulled by the fan flows through the radiator -- greatly reduces this defect. The shroud is less beneficial when the hood is closed, of course, but usually there is still some improvement. Note that increased air flow through the radiator also means increased air flow through the oil cooler, which usually results in higher oil pressure.
Since a shroud increases air flow through the radiator when a car is at idle, it will usually help cooling in a car that spends a lot of time in stop-and-go traffic. A shroud will also improve cooling in any car that spends some of its time at full throttle interspersed with significant periods at idle -- the classic stoplight grand prix. But if your car is in good shape, if you drive in areas where traffic flows well, and if you put the throttle to the floor for maybe ten seconds once a day, you don't need one.
Note that a shroud provides its greatest benefit when a car is not in motion. This is the opposite of a spoiler, which has no effect when the car is at rest.
For what it's worth, my car has neither shroud nor spoiler. It has an absolutely stock cooling system save for a post-JH water pump which may perhaps have the improved impeller (I haven't looked). The radiator is a stock two-core unit. The thermostat is the 82°C version and the radiator cap is in good shape. Ignition timing is 12°BTDC with no vacuum retard. Mixture is to spec or even slightly lean, and the fuel is real gasoline. While the car will certainly get hot if I put my foot into it, or sit immobile in traffic, for long periods, particularly if the air temperature is 95°F or above, it has never yet overheated (defined as venting of steam. or boiling of coolant, during engine operation). And this is in Arizona, which IIRC tends to be a tad warmer than OKC. :^}
Last edited on 03-09-2006 05:06 pm by Mark Rosenbaum