After many years of never having a cooling issue, I've finally found the XJ's match, so here's what I'm planning on doing:

Underneath the radiator, there's a space that's about 22" wide, 6" tall, and about 4" deep. I have found a decent looking bar and plate cooler for about $150. It's intended as an oil cooler, but I'm going to attempt to tee off the heater hoses and run additional coolant through it. Now, I know it won't be thermostatically controlled, but I figured if I need it for towing or some slow speed off-road crawling, I can just open the manual valves going to it and maybe close the one(s) for the heater core to force more flow through the cooler.

I kinda wonder... why hasn't this been done before?

*see attached pic*

Story:

I was coming back from a job site in 100 degree heat, towing a 5x10 enclosed trailer loaded with tools, roof rack with the full size spare, my 2 teenagers (and all their stuff), running about 60 uphill with the AC on. The temps started climbing slowly until about 230, then WHAM. Pegged. Welp, that's it. I pulled over and let it cool a bit, added some bottled water and burped it. Ran fine, and the temps were down around 200 again, so I went on my way. I figured the hills were over, so I kicked the AC back on and ran into another hill. Things were going well so I thought it could handle it. Nope. It crept to about 230, then suddenly it pegged and boiled over again.

Now, I've wheeled in over 100 degrees with the AC on and never had a problem. I've ran numerous trips up and down the interstate at 80, loaded with people and cargo. Never a problem.

Once I got it home finally, I did a head gasket check and a coolant flush... everything's working as expected. Without the trailer, no overheating whatsoever. With the trailer, it's fine until I get a long hill.

 

Most people focus on using better versions of the existing equipment. Using the heater core flow for additional cooling is an interesting approach. It will definitely add capacity, but hard to say how much. Unless you put an efan behind it, you'll only get benefit when the vehicle is moving.

 

That idea is a blast from the past
About half a century ago (really !) my vehicle was a 1967 BMW 1602. It sometimes ran hot in the summer so I got a big heater core of some sort from a junkyard, mounted it behind the grill and in the summer moved the heater hoses from the stock core to this thing. Worked great.

Oil cooler passages are sorta small, fine if you have enough pressure but I wonder if you should consider using a heater core instead. Obviously wouldn't need to be a jeep core, just pick something that would fit.Probably be cheaper too...and would clearly handle the pressure and the fluid.

 

One other comment - I wouldn't tee off the heater core lines. It needs to be run in series with the heater core, either before or after. I'd put it after the heater core.

 

^^^ this was my first thought. And second was the e-fan need. But yes, try a heater core that matches those dimensions and let us know what happens. You could have some tees and ball valves to use it as needed and to to bypass it in the winter.. Very interesting concept.

 

What is your tranny shifter position when you are towing...If in OD....it makes an incredible amount of heat, thus the overheat. You should always tow heavy loads in 3. If you are not in series with one of the pump outlet ports, there will be no/low flow through that cooler. If you put it before the heater core, it will cool and thus reduce the heat available at the heater

 

Yep, that hot transmission fluid will dump a LOT of heat into the coolant. OP, are you running an auxiliary transmission cooler?

 

The **** reads 4


(It's a 5 speed)

 

Man, the number of times I have had to drive old beaters with the heater on in the dead of summer in the South... yeah this idea is as old as it gets. I've put random parts store heater cores zip tied to the grille before and had to make it home like that. Specifically, I remember an old squarebody S10 of mine. After I bought it, I only drove it around town in small trips until I found some Rx7 parts I wanted about 3 hours away. Once I got about 30 minutes in, it would overheat BAD. Long story, but the end problem was that half the radiator was full of solid dirt. I had to get there and back, so I did that (above) and made it the rest of the way.

This oil cooler I found is a bar & plate heat exchanger. The passages are actually larger than a radiator, so my original concern was actually a little on the "it's probably too open" side. IDK, I want something that'll fit nicely in that empty space, and certainly something to add a little more cooling. If it needs fans, I'll add fans. There are little 6" electric fans available.

I figure I won't need the heater during summer, so I'm gonna isolate it and run all the heater coolant through the front cooler, but only when towing. Otherwise, I'll shut it off too. Today it was 104 and nearly 100% humidity. I sat and idled for 45 minutes with the AC on waiting to pick up one of my kids. Absolutely didn't budge from 210.

I'm kinda excited to see how this goes. once it arrives, I'll do a test with the trailer attached, one with the cooler on service and one with it isolated. I have a scan tool that can read the temp sensor, so it'll be fairly accurate. I'm going to go out on a limb and say that I don't think it'll need a fan. I don't know. I guess I'll find out when I get there.

 

Sounds like you’ve been through the wringer with overheating beaters respect for the grille mounted heater core hustle. Your bar & plate oil cooler idea is solid, especially with those wide passages. Tossing it in the heater loop when towing is clever should help without overcooling daily driving.

If it holds 210°F in swampy idle hell, you’re probably golden. Fans might be overkill, but keep ‘em in your back pocket just in case. Stoked to hear how the trailer tests go scan tool data doesn’t lie. Fingers crossed it’s the simple fix you’re hoping for.

 

I'd like to update this thread with some other observations.

1) I haven't had any time to work on it since posting, so nothing has really changed.
2) I was working on another issue that popped up and I noticed something. My winch power cables were severely corroded and quit working, so I was kinda looking at relocating the controller, as I was thinking that maybe it was blocking a little airflow. Then I noticed my AC condenser. Holy cow, that thing is in TERRIBLE shape! It's original to the body at 398k miles. Half the fins are super crooked and the rest is plugged by what looks like big sand grains that I can't blow out. So I'll be replacing the condenser first.
3) It cooled off a TON here, and my operating temps dropped dramatically. It would normally run right at or juuuust below 210. This whole summer it's been looking like it's running juuust above 210 or higher, depending on the load. Today it was running well below 210 in the 70 degree air (what a welcome relief that was, btw). So I'm kinda suspicious of my thermostat now too.

One thing at a time. I'll do the condenser when it stops raining and I'll report back. But this whole week it won't get past the 80s, so it'll be difficult to do an apples/apples test.