Jeeps are weird.

I put a new thermal fan clutch on when I rebuilt the cooling system a few months ago. It started out almost fully locked, no clutch action. Truck was scary loud and the mileage tanked. After 100 miles it loosened up and was only loud over 2000rpm, mileage still sucked, and I could never se existence that it was engaging/disengaging with temp. It just seemed to always be at 75% lockup. The truck also slowly overheats at idle.

Yesterday I'm going the boat on the interstate and the temp climbs to 206-208 and hangs there I stead of the normal 197. I realize that although I'm turning 3k rpm the truck is quiet. I think the fan clutch has blown out so I stop and check it. It's still turning. I figure it wont overheat while moving so I keep on going. Truck stays 206-208 for 20 miles. 

I get off the interstate and  sitting at the first light the temp goes up to 213. As I pull away is obvious the fan has locked up solid. Its loud again and the temp drops like a rock to 195, then it goes quiet again.

Holy crap the fan clutch is suddenly working like it should  after 5k miles.

Of course on the trip home it went back to 75% lock the whole time. 

And the AC stopped cooling like it should. Except at a stop light where it works pretty well, but not like did yesterday.

Jeeps are weird.

That sounds more like your fan clutch is weird. 

Not that Jeeps aren't weird as well. 

Yeah, I think that's just a bad fan clutch rather than a sign of existential brand weirdness.

I think you got a bad clutch from the get go.

Replacement parts that don't function correctly??

I'll agree that it sounds like just a flaky fan clutch.  I'd try another one and chances are, it'll work fine. 

Never match wits with a...fan clutch? 

Vigo said:

Never match wits with a...fan clutch? 

is that were you get baby fans?

Yeah, I figured the fan clutch just needs to go. I was originally thinking about doing a full electric fan conversion but after experiencing a working thermal clutch for one drive I may go that way. I think I may just spring for an OE fan clutch and see what happens. Hell, the last one was fine at 160k, another one will go at least that long.

Today the fan is locked up again and the ac works great. Go figure.

If you can find a newspaper, roll it up and stick it in the fan when running.  If you can stop the fan easily, it is working.   I'd you can't stop the fan, the clutch is locked up.  

In reply to Kramer :

Problem is its locked all the time. Which is a problem for a thermal fan clutch.

Never go up against a fan clutch when death (of your engine) is on the line!

Go for the electric fan conversion. You'll get better efficiency and a fan that's far less likely to fail in a way that causes it to eat through the radiator. And if you put in an on/off/auto manual control switch, the ability to do deep wading without risking any of your fan blades, and redundancy in case of sensor failure.

GameboyRMH said:

Go for the electric fan conversion. You'll get better efficiency and a fan that's far less likely to fail in a way that causes it to eat through the radiator. And if you put in an on/off/auto manual control switch, the ability to do deep wading without risking any of your fan blades, and redundancy in case of sensor failure.

IIRC, he tows with his ZJ.  That makes the electric fan a marginal idea.  I've got one with an e-fan in it and keeping the thing cool under heavy load has taken some work.  The stock radiator is marginally sized and the airflow through it sucks without a mech fan to help out or a lot of hood venting, etc. 

I do tow with it, and that's good to know about the electric being an issue. Part of my wanting to go electric was IMPROVING the towing cooling so I'm glad to read otherwise before dropping the clams on it. The hood is vented now though.

As for deep water...not in the plans for this Jeep. If I can't walk across while keeping my nuts dry then I'm not driving through it. Theres always the oddball trail mistake but the clutch fan should handle that.

https://www.jeepforum.com/forum/f310/anyone-done-clutch-fan-upgrade-4-0-gm-11-blade-plastic-2892193/

After checking this out, it may have some info you are looking for.  I'm interested, since my son and I just picked up 2 XJ's.  Hope it helps.

Yeah electric fans don't push as much air as mechanical fans do at higher RPMs, which can be a problem for oddball cases like the ZJ and its undersized radiator. You'd need very powerful fans (like 40A motors) and well-designed ducting to help make up for the decrease in peak airflow. This is a problem with many Cherokee models, some of which came stock with 40A electric fans or even hydraulic radiator fans.

I'll be ordering a factory fan clutch next time I get paid in a couple weeks. They're 2.5x the cost of the aftermarket ones, but cooling is something that I want to make bulletproof.

ultraclyde said:

I'll be ordering a factory fan clutch next time I get paid in a couple weeks. They're 2.5x the cost of the aftermarket ones, but cooling is something that I want to make bulletproof.

If you want bulletproof cooling, snag one of the Winner Racing ebay 2 row rads.  I threw one in my ZJ a couple months ago and it definitely cools better than any rad I've run before.  It's the thickest drop-in radiator I've found for a V8 ZJ.  

In reply to rslifkin :

I did a full aluminum radiator when I did the rebuild a few months back, I think it's a 2 row... Seems to work well at the moment (when the fan's running anyway) but I'll keep those in mind.