Fan clutch questions

Hi all,

Just wondering how to tell if my fan clutch needs replacing. While driving, it sounds like the fan is almost always engaged. I checked (with the motor off!) and the clutch is not frozen, but the fan is fairly difficult to turn by hand.

Thanks,

Dave

At least it's working properly and cooling the engine. Unfortunately the "roar" from the fan also means that it's sucking up HP and negatively affecting gas mileage.
If you want to get rid of it altogether to gain the lost HP/MPG, replace it with a 14" electric fan and mount it inside the stock shroud. You can find one cheaply on e-bay.

The typical failure for a fan clutch is that the viscous fluid used to create the "clutch" action simple fails to respond anymore. Also, the viscous coupling has a service life of about five years, so that's already a pointer...

The most reliable "test" I've found is to get the engine up to operating temperature, cut it off, and then try to spin the fan by hand - it should be fairly difficult. If it spins easily, the clutch is not coupling. Of course, the suspicion of a fan clutch failure is typically overheating - and you note that temperature drops slightly when the engine is revved from idle to about 1200-1500 rpm (which causes the water to flow faster through the system, and increases its cooling effect somewhat.)

I've only rarely heard of a fan clutch actually "freezing" - the viscous clutch staying coupled all the time - but it is possible, although rare.

Try that test and let us know. If you have to change the fan clutch (as I suspect you might anyhow) you won't need to pull the radiator and such - just remove the upper crossmember holding it all in place and you'll be able to lean it forward a couple inches. This will give you room to clear the studs on the idler hub where the clutch is mounted.

Changing the clutch is a 1 to 2-beer job.

5-90

5-90 said:

The most reliable "test" I've found is to get the engine up to operating temperature, cut it off, and then try to spin the fan by hand - it should be fairly difficult. If it spins easily, the clutch is not coupling.

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5-90 is spot-on, but remember that it's in the 30s and 40s here in CO, so the engine will be fairly cold...drive it around for a good while to warm it up thoroughly before testing.

Replacing the factory clutch fan is much easier than swapping it out with a different system. Your local NAPA, Shucks, Pep Boys, etc should have them in stock for about $35 or so. I’d highly recommend against going to an electric fan. I looked at a bunch and installed 2 different fans and never could find one that pulled enough air to keep it cool. There have been a few people who have done it successfully, but you will need a high quality fan that pulls at least 1200 cfms. You’re not going to find something like that cheap at your local auto parts store or ebay. If you want to replace your clutch fan with something else I’d suggest using a flex fan. I’ve been using a Perma Cool 15” reverse rotation (why do Cherokees have to be different?) flex fan with a 2” spacer. At cruseing speeds I can tell no difference between the flex fan and the clutch fan. At idle/crawling speed the difference is huge. The flex fan pulls more air than the clutch fan ever thought of. Before, when I’d sit in line for the ATM behind a bunch of cars the engine would start getting hot. Now I can sit in traffic all day with out a problem. The 2” spacer works well with the factory shroud, but I get a little bit of rubbing when I’m 4x4ing. If you plan on doing a lot of off roading the 1 ¾” spacer will give you more clearance and still pull more air than the factory set up. BTW When I replaced mine it wasn’t necessary to remove the radiator cross member. I just unbolted the fan shroud and clutch fan assembly and removed the whole thing as one unit out the top.

Yucca-Man said:

5-90 is spot-on, but remember that it's in the 30s and 40s here in CO, so the engine will be fairly cold...drive it around for a good while to warm it up thoroughly before testing.

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I checked it when the motor was cold and the fan was pretty hard to turn. I'll try 5-90's test this weekend.

Thanks!

Wiley Coyote said:

I’d suggest using a flex fan. I’ve been using a Perma Cool 15” flex fan with a 2” spacer.

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I will have to look closer, but my fan looks a lot smaller than 15". I have A/C, and it has two fans side by side, the primary belt driven fan, and a electric fan.

The XJ isn't different - pretty much anything running a flat belt has a reverse rotation water pump.

I think it's because the water pump is about the least-power-robbing accessory under the hood (after all, it's only a flow pump and doesn't have to generate pressure...) and it therefore does double duty as both an engine "accessory" and an idler pully for belt routing. Therefore, it is driven off the back of the belt.

Did you have a hard time finding the flex and spacer? What is your cooling like at highway speed? The problem I've noticed with flex flans is that, since htey are designed to "flatten out" at high engine speeds, the flat spinning blades tend to block off more airflow than they provide.

I'm designing a spacer to replace the fan clutch entirely, deleting a component subject to failure and allowing the re-use of OEM parts. Interested?

5-90

Crown said:

I will have to look closer, but my fan looks a lot smaller than 15". I have A/C, and it has two fans side by side, the primary belt driven fan, and a electric fan.

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Your right, the factory fan is smaller than 15”. It has a dogleg looking kid of deal on the blades and sits pretty deep in the fan shroud. The larger flex fan sits closer to the engine side of the shroud (still inside it), but will clear it just fine. All Cherokees are set up the same way; mechanical fan and shroud on the passenger side and an electric fan on the drivers side. BTW If you want to see a little trick on how to make the electric fan come on sooner take a look at Dr Dino’s site

http://www.angelfire.com/my/fan/CTS.html

5-90, I had to order in the flex fan and spacer, but that’s not unusual for AK. I’m not sure if a good store in the lower 48 would have it in stock. Make sure that they don’t try to give you a fan for a Wrangler with a 4.0, they are not the same. I like your idea about the spacer and apparently the big companies do too. When I was looking for my flex fan I ran across a spacer like that. I can’t remember if it was Perma Cool, Flex-A-Lite, or some one else, but they make one. I wouldn’t use it with the factory fan. I have a buddy that has a TJ with a 4.0. While we were out 4x4ing his clutch fan gave up the ghost. We welded the fan to the backing plate. Not the best way to do it, but it was good enough to get him home. Having the factory fan turning all the time seemed to bog down the engine. It wasn’t real bad, but there was a noticeable loss of horsepower. If you could use a lighter fan with less pitch on the blades I bet it would work better. By the time its all said and done, I think you would be right back where I’m at now with a flex fan and a spacer.

Wiley Coyote said:

5-90, I had to order in the flex fan and spacer, but that’s not unusual for AK. I’m not sure if a good store in the lower 48 would have it in stock. Make sure that they don’t try to give you a fan for a Wrangler with a 4.0, they are not the same. I like your idea about the spacer and apparently the big companies do too. When I was looking for my flex fan I ran across a spacer like that. I can’t remember if it was Perma Cool, Flex-A-Lite, or some one else, but they make one. I wouldn’t use it with the factory fan. I have a buddy that has a TJ with a 4.0. While we were out 4x4ing his clutch fan gave up the ghost. We welded the fan to the backing plate. Not the best way to do it, but it was good enough to get him home. Having the factory fan turning all the time seemed to bog down the engine. It wasn’t real bad, but there was a noticeable loss of horsepower. If you could use a lighter fan with less pitch on the blades I bet it would work better. By the time its all said and done, I think you would be right back where I’m at now with a flex fan and a spacer.

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I'll have to look into that, I've not seen an aftermarket spacer that used the OEM fan. Do you have any notes?

As far as the electric fan coming on quicker, I just tapped in an override switch in parallel with the thermal switch in the radiator tank - I can turn it on withthe AC, the thermal switch can engage, or I can turn it on at will with a switch. This is easy to do with the RENIX (just wire a toggle in parallel with the thermal sender) but it can be done with HO if you provide an "ON" signal to the electric fan relay as well.

5-90

Wiley Coyote said:

There have been a few people who have done it successfully, but you will need a high quality fan that pulls at least 1200 cfms. You’re not going to find something like that cheap at your local auto parts store or ebay.

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Yeah, and I'm one of them.
My primary fan is a 14" high performance electric unit that I bought locally but you can find an identical one on e-bay for about 50 bucks. It pulls 1800cfm.
My secondary fan is the same auxiliary electric fan with the curved blades that's fitted to '97+ XJ's. Both fans are wired to switch on at the same time. The current draw isn't that much and my stock alternator can keep up easily.
Between the two, there's enough airflow to keep my stroker cool even in the middle of a 120*F summer.
__________________________________
Dino's "Mean Green Machine"
1992 XJ Laredo 4-dr - 4.6L I6 HO Stroker - 178k miles - AX15, NP231, D35c, D30

258hp@4800/320lbft@3200, 1/4 mile = [email protected], 0-60 = 5.9secs
Websites - Jeep 4.0 Performance, 4.6L Stroker Build-Up, Dino's Jeep Tricks

5-90, Perma Cool is the one that I seen, unless someone else is making them too. They are calling it a fan clutch replacer. Here is a link:

http://perma-cool.com/Catalog/Cat_page23.html

I’m not sure which one you would need to use. It has several notes about reduced gas mileage and not to use over 4200 rpm or on high performance engines. I’d think real hard before you decided to try one out.

Dr Dyno, I bet that having both fans come on at the same time helps quite a bit. I didn’t try that. I just replaced the mechanical fan with an electric one and wired it to a temperature sensor. The two fans worked independent of each other, but wouldn’t draw enough air to keep my engine cool. Do both of your fans come on with your AC or defroster as well?

Interesting, but I'm not wild about its design.

Too many corners, and too many fins and other air-catchers for something that gets spun around behind a fan. I may go ahead and have mine made anyhow - a short run - and see what's what.

Definitely not something I would have designed - it's just not aerodynamic enough (even a little power lost is still power LOST - especially when it's not doing something useful!) and I just see too many weaknesses in the design...

Thanks, tho!

5-90

Yea, I can see what you mean. I wasn’t overjoyed with it either, that’s why I went with the flex fan set up. I like your electric fan set up. It would be nice to be able to turn it off completely for water crossings. Right now I’m running something similar to Dr Dyno, but with a potentiometer instead of a resistor and an off switch, so I can go back to the factory setting. The potentiometer makes the turn on temperature for the fan adjustable. I have mine set to come at about 190 degrees. It works pretty well. The flex fan seems to do fine in water crossings. I think that the blades just flatten out when they hit the water. At any rate it hasn’t been a problem.

Wiley Coyote said:

Dr Dyno, I bet that having both fans come on at the same time helps quite a bit. I didn’t try that. I just replaced the mechanical fan with an electric one and wired it to a temperature sensor. The two fans worked independent of each other, but wouldn’t draw enough air to keep my engine cool. Do both of your fans come on with your AC or defroster as well?

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Yes, they both come on together when I use the A/C, defroster, and when the coolant reaches 210* (not 220* because of my CTS resistor trick).

http://www.angelfire.com/my/fan/CTS.html

Wiley Coyote said:

5-90, Perma Cool is the one that I seen, unless someone else is making them too. They are calling it a fan clutch replacer. Here is a link:

http://perma-cool.com/Catalog/Cat_page23.html

I’m not sure which one you would need to use. It has several notes about reduced gas mileage and not to use over 4200 rpm or on high performance engines. I’d think real hard before you decided to try one out.

Dr Dyno, I bet that having both fans come on at the same time helps quite a bit. I didn’t try that. I just replaced the mechanical fan with an electric one and wired it to a temperature sensor. The two fans worked independent of each other, but wouldn’t draw enough air to keep my engine cool. Do both of your fans come on with your AC or defroster as well?

Click to expand...

I bought my fan clutch spacer/replacement at quadratec for something like $10. They only had one model for the XJ at the time and it fits perfectly. Works reliably and I never need to worry about replacing a fan clutch again. I put it in at the same time I installed a new 1-core aluminum radiator, so not totally sure which of the two solved my severe overheating problem.