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Another Cooling Issue Thread - 99 Cherokee 4.0

TxBxSx

NAXJA Forum User
Location
TX
A lot to unpack here, but here we go.

I picked up a 99 4.0. First drive it ran at about 220 for 3 hours straight. I popped the cap to check coolant condition...while it was still a bit warm and it puked brown orange coolant everywhere. Afterward, I could hardly drive the thing without it overheating. (Assuming I had air in the system after topping off with water) This being a replacement for my 94, I knew we deal with cooling issues and opted to do a full cooling system upgrade, as well as replaced the head due to the fact that the original head had so much rust scale in the coolant passages, and I had an extra 99 head on hand.

New set up includes:

Mishimoto Aluminum Radiator
OE mechanical fan and Aux fan
FlowKooler High flow water pump
Mishimoto 180° thermostat
Mishimoto 19 psi Cap
Mishimoto Radiator and Heater Hoses

I flushed the cooling system probably 7 times using Prestone Cooling system cleaner until the water finally started draining clear, and there was almost no scale on the drain plug magnet. Compression is 155-165 on all cylinders. No smoke. Engine oil and Trans fluids are clean. The last Prestone flush I ran for a couple weeks, and it was running probably 190 pretty solid. I even towed our pop-up camper a couple hours away and had no issues. It did creep up to 220 on the way back, but I somewhat expected it to do so with the 2000# trailer.

All was well until I went to swap the flush mix for 50/50 coolant mix. First drive it got right up to 220 under easy driving conditions and has been doing so on short drives since. Long drives bring on a boil. I would park on incline, let it cool and make sure that if any coolant was slurped from overflow it was restored to "Full", but this never got better....leading me to believe air in the system wasn't the issue. Today, when trying to make a 45 min drive in 75° weather, the temp gauge would get to 180 and then slowly creep to 220-225 and hang there till it would lurch and the "check gauges" light would come on (I'm assuming this is a safety feature built into later models intended to catch peoples attention). I knew what we were in for, so I grabbed a few gallons of distilled water while it was cooling down.

I let the overflow drink, we drive 10 min it boils over again, repeat. We drive 25 min it boils over again, repeat. By this point a significant amount of coolant has been left behind and replaced with water. Now, we drive home 45 min and ride at 210 while on the move, 215 while at stop lights, and it recovers to 210 when we get moving again.

This is telling me that this jeep doesn't like 50/50 coolant if I'm following the trends.

I have tried other things. Different thermostats/no thermostat with 50/50, resulting in overheat. Mishimoto Electric fans/shroud, overheated with these but ran fine when OE fans were swapped back in (I'm about to test CFM on these, because they felt nothing like 950 cfm EACH). It just blows my mind because I've covered all the bases (pressure tested and checked for combusion gases) and put some good parts in, but my 94 was rock solid at ~185 most all the time with nothing more than an "HD" radiator from the parts store...and I could even get away with the aux fan being dead during weather like today.

This jeep has been my nightmare, and I feel a bit bonkers saying the only way I can get it to run cool is by running all, or mostly water. What the heck?!

Thoughts anyone?
 
Run it, burp it, run it burp it, etc. It takes 4 or 5 burps to get all the air out. Flowkooler is a good pump, Hesco has a better one. I can't see where coolant should make any difference. I run a high compression, 4.1 at 6k feet with a 20 year old cheap aluminum radiator pushing a heavy beast on 35's with a Hesco pump, and it barely gets warm.
 
Make sure the cooling system is not allowing air to enter. The radiator cap should be rated 16 lbs and a good quality part. I would also look at the frost plugs to make sure none have any pinholes, especially on the backside of the head and block.

Make sure the head gasket is not allowing combustion by-products to enter the coolant.


.
 
The Mishimoto radiator for the XJ is known for clogging. Toss in a Spectra Premium single row ($120 on Amazon), and see what happens.
 
Yep, dump the mishimoto, put in a spectra; put in a 195 super Stat, regular water pump. Cap is not a big deal, I've been running a 8 psi cap for years.
 
Update, I noticed a small coolant leak last night.

After rinsing everything off today and idling it up to temp in the driveway I was watching some new bubbles purge from the system into the overflow tank. I found the source of the leak to be coming from the inlet tank of the radiator, and the bubbles stopped as soon as the radiator started dripping.

After shutting it down I could hear the leak in the radiator sucking air.

I've sent Mishimoto an email requesting a full refund of the essentials kit I purchased, and I will be trying again with the Novak Conversions radiator. I'll start with just the radiator this time, and when that has proven itself capable I'll add a series of quality e-fans. Possibly SPAL fans, or if I have room I'll try and put in a couple of Taurus fans.
 
My last Cherokee ran 190 on the day to day, but when I went out on solo runs in the mountains at 10k elevation, crawling at low speeds for hours it would get hot enough to lock up the motor until it cooled down. I’m aiming to not have to worry about it anymore, and have room to compensate for a high compression stroker build while I’m at it.
 
You're still overthinking the situation. For now, ditch the Mishimoto, and see how it goes with the Spectra on the OE fan config.

BTW, there are definitely variations in the cooling performance associated with the available fan clutches and efans. The USMW 22148 fan clutch is midway between a stock 4L fan clutch and the ZJ fan clutch. The Autozone Duralast 922625 is the same fan clutch. The late model many-blade efan (e.g., the TYC version) flows significantly more air than the early model 5-blade efan design. So there are many things you can do before experimenting with Novak radiator and fans which in my opinion will not cool any better than a solid OE setup.

Once you verify that you have solid cooling performance with the Spectra Premium during daily driving, but a manual switch on the efan for offroading at low speed.
 
A clean, factory cooling system will keep a stock xj cool in whatever you can do with it. I can carry a full load of mail in 105 degree temp, with the ac running all day long and not even whiff over heating. Spectra radiator, duralast pump, 195 superstat.
 
I've read this many times, and for the sake of just getting this thing on the road I'm going to go ahead and swap a Spectra Radiator in to see where we stand. I'll report back by this weekend hopefully.
 
Update:

Swapped in a spectra radiator, 195 thermostat, and 16 PSI cap. Running about a 70/30 mix favoring distilled water. Idled for about a half hour with a no spill funnel in place and never even got to 210°. I also went ahead and pulled all the mishimoto hoses and swapped in all gates molded hoses.

I ran it for over an hour. Pushed it hard on the highway, long pulls under heavy acceleration up to 90 mph and running the ac the whole time. Still stayed below 210°. Its currently 60° outside here, so we'll see how it holds up when it heats back up. After all this headache, I'm just going to run what seems to be working until I see an issue and sending every piece of Mishimoto components back for a refund.
 
The fan clutch is not a new component, but one I pulled from my 94 as a known good component. Never paid attention to part numbers on it.
 
At some point I’ll probably go ahead and wire up a manual bypass switch for the aux fan. I already have an extra switch in a switch panel on the dash, and an extra relay in my power distribution block under the hood, so it’s just a matter of running some wire.
 
Stock setup for the win. So many XJ people go to great and expensive lengths to cool their 4.0 but in reality a clean and fully functional stock setup is best. Glad you got yours sorted out.
 
PS I upgraded to a radiator with a filler neck verses my stock Renix type pressure tank cooling system Conversion is easy and it rids me of that prone to fail plastic pressure tank. I put a standard generic overflow tank in the jeep near where that pressure tank and its shelf used to reside.
 
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