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Old 12-28-2013, 03:10 PM   #1
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Fan Blade Hitting Shroud

I think I have it rigged up now, but what would make my fan blade hit the top of the plastic shroud around it? It doesn't feel loose at all but it was rubbing it enough that it cracked the shroud. 99 TJ with the Four cylinder and a four inch lift.

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Old 12-28-2013, 03:21 PM   #2
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When you lift the suspension 4", you must make some adjustments to the angle of the rear driveline to prevent the u-joint from seizing. This typically involves a transfer case drop spacer. As you drop the transfer case, the transmission and engine tilt backwards, raising the front of the engine. This tilt causes the fan to contact the shroud at the top.

To fix the problem, replace or repair the shroud (it is an absolutely critical cooling system component) and drill new holes to mount it higher until it is centered in the shroud opening.

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Old 12-29-2013, 01:52 AM   #3
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Could also be from a body lift if you have one. Same principle but instead of the engine pushing the fan up from a TC drop, the body is pulled up by the body lift, hitting the fan.

To truly "fix" the problem would be to do what needs to be done geometry wise to center the fan again. Maybe a Motor Mount Lift, a smaller body lift, or SYE.
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Old 12-30-2013, 03:41 AM   #4
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Could also be from a body lift if you have one. Same principle but instead of the engine pushing the fan up from a TC drop, the body is pulled up by the body lift, hitting the fan.

To truly "fix" the problem would be to do what needs to be done geometry wise to center the fan again. Maybe a Motor Mount Lift, a smaller body lift, or SYE.
That's definately NOT his problem. If he moved the body UP from the frame, the fan would hit the bottom of the shroud. In his case, the engine is tilted back at the engine mounts, so the fan goes up and chews on the top of the shroud.
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Old 01-01-2014, 11:40 PM   #5
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Better yet, yank the shroud & fan out, install a quality electric fan, and gain a few HP for your 4-banger. It almost certainly needs it.
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Old 01-02-2014, 12:35 AM   #6
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Originally Posted by KaiserJeep View Post

That's definately NOT his problem. If he moved the body UP from the frame, the fan would hit the bottom of the shroud. In his case, the engine is tilted back at the engine mounts, so the fan goes up and chews on the top of the shroud.
Didn't realize it was hitting the top.
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Old 01-02-2014, 12:36 AM   #7
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Better yet, yank the shroud & fan out, install a quality electric fan, and gain a few HP for your 4-banger. It almost certainly needs it.
You will actually lose horsepower and won't be moving as much air as the stock mechanical fan does. Electric fans are only good for turning off easily in deep water or after an engine swap where the stock fan wont work.
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Old 01-03-2014, 03:11 PM   #8
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I've seen a lot of back-and-forth discussion on the horsepower issue of electric fans, but here's a guy who actually used a dynamometer and (from what I can tell) did it right. He wasn't using a 2.5L 4-banger in the test setup, so obviously the overall numbers would be different, but the general results, which probably hold true in most cases, show that an electric fan requires significantly less effort from the engine's point of view.

Dyno testing on fans, alternators and oil.....all here!

If anyone has other dynamometer test results that show otherwise, or better yet are Jeep-specific, I'd love to see them.

Bear in mind that I'm coming at this from the standpoint of my own experience with a 2.5L, which has been that it performs acceptably around town, but poorly on the highway, at high(er) speeds and RPMs, which is where the HP gains from an electric fan are typically the most significant. For rock-crawling, when you're in 4L anyway, the cooling benefits of an electric might be attractive, but any HP gains will likely be negligible, so it's more of a toss-up to personal preference.
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Old 01-03-2014, 03:13 PM   #9
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Unless you use a more efficient alternator, its not really possible. Energy is lost in the process. Nothing is 100% efficient and adding one more element only loses power
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Old 01-03-2014, 04:08 PM   #10
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Also, what CFM was the electric fan that was tested? I doubt the electric fan used was able to pull as much as a mechanical fan. The difference may make no difference for some but for those crawling in desert temps, a few hundred more CFM could make all the difference.
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Old 01-03-2014, 04:13 PM   #11
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It's not just about electromechanical energy conversion. The power requirements of a belt-driven fan are greatly influenced by the engine RPM, the fan clutch, and the vehicle speed. Electric fan power requirements are really only influenced by the vehicle speed. This is why dynamo tests consistently show that electric fans save HP at higher RPMs, where belt-driven fans eat more power. Plus, the electric fan turns off when it's not needed--meaning it often requires zero HP. There's no way to turn off a belt-driven fan like that, even with the best of clutches.
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Old 01-03-2014, 05:27 PM   #12
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All aftermarket fans I have dealt with change their RPM based off of coolant temp. Do fancy ones tie into your computer to measure speed?
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Old 01-03-2014, 06:45 PM   #13
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No, it's just easier for either type of fan to pull moving air, IOW either one will require less power when the vehicle is moving forward--though how much that affects power usage, I don't really know--even that depends on blade pitch & area. And I was thinking in terms of a temp-based "on-off" fan; I'd figure a temp-based variable-speed electric would be the most efficient overall. I'm looking for more comprehensive data on the effects of RPM/vehicle speed/etc. on overall fan efficiency, but they're hard to find. So many variables. Sheesh.

Looking at the (arguably sparse) data I can find, it really seems to boil down to the type of driving you're doing, and how your engine is running, that really determine whether electric or belt-driven are the best choice. Then there's price.

I know we've totally hijacked this thread, but it's interesting stuff to consider. In some ways it's like trying to figure out how many licks it takes to get to the Tootsie-Roll center of a Tootsie-Pop. The world may never know.

(And if you get that reference, you're approaching Old Fart status.)
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Old 01-03-2014, 06:58 PM   #14
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I did the conversion. I wired it so it can let run off the inline thermostat OR hit a switch and the fan runs on high regardless of the inline thermostat. So when I'm rock crawling, moving at 3-5 mph at low RPM's my fan is working on high regardless of RPM. On high the fan is rated at 3300 CFM. I like the set-up.
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Old 01-03-2014, 07:25 PM   #15
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I did the conversion. I wired it so it can let run off the inline thermostat OR hit a switch and the fan runs on high regardless of the inline thermostat. So when I'm rock crawling, moving at 3-5 mph at low RPM's my fan is working on high regardless of RPM. On high the fan is rated at 3300 CFM. I like the set-up.
Yeah that's a good CFM rating. My friend is currently running two 1600CFM fans on his bored 350 and wondering why it over heats in the summer at low speeds. CFM is key
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Old 01-03-2014, 11:00 PM   #16
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I also did the electric conversion. I used a Flex a lite black magic fan/ shroud combo. It definitely helped with the pulling power of the jeep at highway speeds in top gear.
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Old 01-04-2014, 12:08 AM   #17
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To fix the problem, replace or repair the shroud (it is an absolutely critical cooling system component)
Why is the shroud so important???
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Old 01-04-2014, 12:12 AM   #18
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Why is the shroud so important???
Because it allows the fan to pull air through the whole surface area of the core.
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Old 01-04-2014, 12:49 AM   #19
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Because it allows the fan to pull air through the whole surface area of the core.
Ahhhhh instead of from each side and such... Thanks! Reason I ask is because i took a body lift off my jeep recently and had to trim a little of the shroud. Was just curious
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Old 01-04-2014, 01:03 AM   #20
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Ahhhhh instead of from each side and such... Thanks! Reason I ask is because i took a body lift off my jeep recently and had to trim a little of the shroud. Was just curious
No. If you run without a shroud you will only be pulling air through the core right where the fan is located and it will be minimal air flow at that. You will only be cooling the water as it passes through the core as it passes directly in front of the fan. You end up with hot spots on both sides of the fan.

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