I've replaced a bunch of pieces of my cooling system....
about 1-2 years ago:
- new CSF 2 row all metal radiator and OEM hoses and fan shroud
- new OEM thermostat and housing
- new OEM radiator cap

recently:
- new OEM water pump and metal heater pipe
- cleaned and backflushed gently the heater core
- new OEM electric fan

The only thing not replaced is the fan clutch, and the rubber heater hoses which are in good condition. Coolant is fresh, nice and green, not brown.

Symptoms are: sits at 210 in traffic, all around town

I drove it today towing a small cargo trailer (4x4) almost empty, at around 50-60 MPH. With the AC on, it was hitting 220-230 (two ticks back from the red tick, or one tick more than 210). Outside temp was only 74.

I was in overdrive/4th, but that shouldn't be an issue towing such a small trailer.

I plan to test it at highway speeds with and without AC, both with and without the trailer, and trying 3rd gear non OD with the trailer too in case OD is too much for the tranny and that is heating up the fluid a lot...

Considering shotgunning/replacing the fan clutch. I know about the NAPA HD ZJ clutch but not sure about clearance with the CSF 2 row.

I have a long tow, about 5 hours, in hot weather, in 2 weeks time and would like to ensure I don't have any issues on the road.

Anything else I am missing?

 

I like your diagnostic plan.

I think the fan clutch is a good idea just 'cuz, but since your problem is on the highway, that's not it.

Trans might be slipping more than you think, which will generate heat. An external trans cooler plumbed in BEFORE the radiator will dump a lot of heat before it gets transferred to your coolant, but that won't fix a slipping trans. You need to find out if your TC is locking up correctly.

 

To test if torque converter is locking up correctly at speed, do the following:

1. Drive at a steady 55-60 on level ground in 4th gear
2. Note the engine RPM (should be somewhere around 1800-1900 on a stock XJ)
3. Tap the brake pedal (enough to engage the brake light switch)
4. RPM should jump up by about 300-400
5. After a few seconds it should come back down to the originally noted RPM.

The jump up in RPM by 300-400 is the torque converter lock-up clutch disengaging allowing the motor to spin a little faster than the transmission input. It will unlock anytime the brake switch is tripped (among other things). After a few moments, the lock-up clutch will be re-engaged and the motor will drop back down in RPM as it becomes linked to the transmission rotation speed again.

 

It is definitely engaging, I did note that as I was driving last night, though I wasn't towing... I'll watch for that too.

 

First test results:

- ambient 82 deg, towing a full trailer (it is 4x6 not 4x4) on flat ground with AC on gives about a needle width over 210.
- any kind of hills (i.e. moderate, not very steep), with or without AC it climbs to one mark above 210
- I was able to drive a loop and cool it down and repeat this. With the AC off it takes a little longer to heat. So I am using AC just to add more heat into the engine to stress it quicker.
- no difference driving in D or 3. If I recall overdrive works on both 3rd and 4th. But with any kind of load going up the hill, it disengages OD and shifts to 3rd, so I don't think driving in 3rd everywhere will solve the problem
- the faster I drive (eg 60-70) the more quickly it heats up

Hard to tell if it is engine load or transmission temp making the difference. No transmission temp warning lights, and it has new fluid in it.

I should also mention I just installed a skid row engine/trans skid plate which covers from just behind the front axle, back to the trans x-member.

Also the radiator intake is partially blocked by driving lights and winch/license plate (ARB bumper). There's still plenty of open space.

Other data point is, when the engine shuts off, the radiator fan freewheels for about 4-5 seconds, doesn't come to an immediate stop, so even though I know freeway overheat is less likely to be the fan clutch, people have resolved issues like this by replacing it.

The 99 XJ FSM says the fan clutch test is to block the grille, run engine at 2400 RPM and watch fan RPM with an optical tach change as it goes past 160-180F. (Not the move the spring 90 degrees lockup test)

About to head out without trailer load to see if it behaves the same way as with the trailer load.

 

Basically the same without the trailer. It was a little warmer outside (88) so it hovered around half of a mark above 210 until I went up some hills then it hit a full mark above 210.

Another question: is this normal? Do I need to fix it?
I'm worried about towing in 100F weather....

I'm going to look at the ZJ fan clutch and see how much closer it would move the fan to my CSF 2 core...

Forgot to mention this is a very low mile XJ 112,000 miles from a little old lady in Ellensburg WA who drove it to church every Sunday. It has been maintained but not a lot of preventative stuff. I'm assuming the fan clutch is original from 1999 at this point.

 

My jeep overheated, coolant was coming out between the head and the block. When I pulled the head all the coolant passages on the head gasket going to the cylinder head were clogged up solid. I had flushed the coolant when I first got it a few years back and the coolant was good. Not sure it it was a slowlingh building up or what. That could be an issue though.

 

At highway speeds i'd think the fan clutch is negligible.
Does the electric fan ever come on especially when the AC is turned on?

 

That's true, I did backflush the heater core but not the block.
The heater core produced a pretty yucky chocolate milkshake, big thick chunks.
But when I replaced the water pump and thermostat, inside the block looked quite good.

I might try some of that radiator cleaner from NAPA at some point and backflush the block.

 

Electric fan comes on always with AC, and about 215 without AC, at least in my XJ.

I agree on the fan clutch but there are plenty of threads here where people say "it can't be the fan clutch because your overheating is at highway speeds" and then they replace it and it fixes the problem. So I don't know!

Something is making the cooling system marginal. At this point the only two things not touched are backflushing the block, and the fan clutch.

 

Agreed. Can't hurt to replace that fan clutch. I have heard of the ZJ mod, but really, if everything it working, the stock system does a great job. I have towed beyond the recommended limits in hot weather with nary a problem.

 

OK, that's good to know as a data point!

 

Replaced the fan clutch. It was about 84 today, and it "seemed" better going up the hill, basically 2 needle widths above 210, but then when I drove home on the flat highway at about 65, it went up about half a notch from 210. It did seem more stable (slower to move) though.

At this point I've run out of time. Will just have to see how it handles the eastern WA temps and towing and passes...

At this point the remaining work items would be:
- backflush block
- look into a bigger trans cooler
- look into HD fan clutch

 

Replace it. BEEN HERE DONE THAT FIXED IT.

 

+1!!