Towing with a modified XJ - a review

I'm mostly writing this because I need to decompress a second before I get in the shower. I hope, though, that this helps somebody else to avoid the mistakes I just made.
First off, the XJ: 2100 CFM Electric fan swapped in, set to come on when the ECU tells the AC fan to come on right around 220 degrees. Cold air intake, manifold-back exhaust in 2.5", injector update, automatic, factory tow package. ZJ rear brakes.
The trailer: Uhaul 6x12 (2k empty) 1/2 full of tools & car parts, 1/2 full of usual household crap. No idea how heavy it was when full, though I'd be surprised if it hit 5K.
The route: Out of Berkeley, CA. Through the Central Valley (100 degrees or so outside) & up into the foothills. Long grades up to 10%, some traffic, elevation to 3,000 feet.

My results: Getting out of Berkeley was surprisingly easy. I just put the car in Drive and it would go - it got the freight moving easy. Stopping also fine, steering likewise. So far so good. As soon as I hit the first grade, though, it became clear the 4.0 wasn't up to the task. Temps climbed steadily until 220 or so when, doing 45 mph on the interstate, the fan kicked on & temps as well as speed stabilized & I got over the hill. Things were uneventful until Auburn, CA when the rest of the hills came in. Once in the foothills, I really had to watch throttle opening due to pinging. Temps would hit 220, fans come on, temps keep climbing. Speed was an issue - the Jeep really didn't want to break 40 mph at times but would do so if flogged. Second gear made a few unwelcome appearances. Oil pressure was lower than usual at times due to increased temp (I think). More pinging.
Had to pull over & leave the engine running 2x to let the fans ever-so-slowly bring the temps down. Never over heated but not for lack of trying.

So, what I learned from this and what I'd hope to relate to others is three things.
1. ) 2000 CFM is not enough for an electric fan swap. Not if you are towing in the summer, anyway. I'm now on the fence between putting my mech fan back on, or going to the Taurus fan I've got in the shed. Also, 220 is a bit late for fans to come on under heavy use (though I'd never had a problem in town)
2. ) You should use higher octane gas if you plan on wringing out the XJ. If I'd known it would ping, I would have used mid-grade
3.) A max tow rating of 5,000 doesn't mean you want to tow 5,000 lbs with the XJ. Or even close, really. Running hot isn't the only problem I had. With the 4.0, you'll have your foot buried in the gas & still be limping up hill at 45 mph.

I've now got to consider realistically how much towing / heavy use I'll be asking of the XJ in the future, and whether what I really need is a K2500 Suburban.

I would bump the fan turn on down a bit. What other mods do you have to the engine? Transmission cooler? It shouldn't be pinging, but later years can ping with some mods.

I occasionally towed about 4500 lbs with my 91. Never pinged or got hot... stopping could have been better. It had the Bendix system, which I feel stopped better, but in the end its an unreliable pos system.

And this surprised you? Its a 3500 pound vehicle. Yes, it can pull 5k, but that is the max rating for a good reason!

Also, if you really had half the trailer full of tools and car parts, there is a good chance you were well over 5k.

98stocker said:

And this surprised you? Its a 3500 pound vehicle. Yes, it can pull 5k, but that is the max rating for a good reason!

Also, if you really had half the trailer full of tools and car parts, there is a good chance you were well over 5k.

Click to expand...

I had an idea that I was pushing it but didn't really understand how hard.
I'd say the first 3 or 4 feet of the trailer were stacked 5 foot tall with tools, parts & books. The rest was furniture, shoes, etc.

My cooling setup has always been fine around town. This weekend, I don't know if fans coming on earlier would have done it. I'm also hesitant to put the on temp too low because, as far as I understand it, the computer runs richer at cooler temps. If I'm going for efficiency, I want it to run at the factory set 210 or so.

All I've done to the motor is exhaust, cold air intake, electric fan & upgrade injectors. Trans cooler is about 4x12x3/4, whatever the factory tow package included. ZJ rear brakes + trailer brakes were totally sufficient for stopping, provided I planned ahead a bit. Got deeper into the pedal than normal but not scary.

I wish I had put some of my trailers on the scale. I did a lot of way overweight towing with my stock '98 2wd xj in the Texas summers for 3 years, not big hills, but some hills. Sometimes really scary without trailer brakes. Trailer brakes are really really nice. I found that you either had to be running 50mph or up between 75-80mph, really had to be up in the powerband so to speak above 2500 rpm, and it would move right along
At 200k on the odometer, It was getting tired with low oil pressure and finally started running hot. I cash for clunkered it in 2009, worst automotive mistake I ever made. It took me 3 years and 2 trucks before I found a decent xj again, Now I have 4 xj's and I don't think any of them are as strong as that first one I had.
Did you ever get yours up to speed? in the higher rpm's

What size are your tires, what ratio are the axles ... for towing you want deeper gearing to take the stress off the motor and trans.

the fact that the temps climbed and kept climbing even with your fans running means you either need the primary starting much sooner, or bigger fans. I would opt for more fan/flow ... for towing I'd go back to a mech fan. What works around town means squat towing. Also shift to 3 when towing uphill to keep the trans from running too hot ... in OD (lockup) the trans will make a lot off heat under load.

My XJ holds it's own pulling a load (usually the tent trailer or my quad trailer), I have a big trans cooler and a stock cooling system. Never had any issues pulling with it, and we have some pretty rough grades here on the Island. The deeper gearing with larger tires puts it back to just above stock specs so it has a bit more gearing torque. My MJ is a far better tow vehicle though with it's 5spd (although it does have the worst 5spd possible).

Owners manual says tow in ""3"" with an Auto.
If you don't the torque converter will create tons of heat.
When towing, you will actually get worse gas milage in ""D"" than in 3.

I've towed up to the 5K rating without issues and a 4.5" lifted 98 with stock 3.55's and 31's. worked just fine.

To truly get a good grasp on what was happening, you need a transmission temperature gauge.

I suspect you were pushing the XJ a tad hard and it wasn't locking the torque converter (or it was, but just on and off as you pushed it harder). These aw4's generate a lot of heat when they're not locked and I believe that is why was pulling your engine temps up since they share the same radiator.

Solution would be to drive in 3 to ensure the TC has a better chance of staying locked, or install a lockup switch so you can do it manually. You would be surprised at how quickly a locked TC can cool down the transmission temperature and when that is cool, then your rad can work more efficiently at cooling the engine.

In my experience, what my Dad always called his "engineering eye"--for judging weights and other measurements, tended to be less SWAG--scientific wild-ass guess--and more WAG.

If you go with the dual-speed Ford fan upgrade, don't forget your alternator and wiring may need upgrading too--those Ford fans pull like 40 amps on high.

I was in 3 the whole trip.
I think I'll upgrade mains when I put the Taurus fan in. Till then I'm going to run the much fan.
I made the same trip today without the trailer. No drama, never ran hotter than 215, plenty of power. Towing. Who knew?
Used to pull a twelve foot camper... barely knew it was there.