WillyXJ

Hello folks.

Earlier this year I swapped in a Golen 4.6L stroker and since have been dealing with methods of trying to keep it cool. Loads of forum threads I've read on the topic through CF, NAXJA, and JeepStrokers. Lots of them say to do this or that and so far none have worked for me. So, I've started my own thread to document my changes to see what works and what does not.

The vehicle:
1998 XJ
AX15
NP321
4" lift, 32" tires
With a full tank of fuel and me it weights 4,600lbs -- loaded for camping is easily 5,200lbs
Both fan shrouds are in good shape
Stationed at 5,230ft above sea level

The test:
When the air temperature is above 85ºF and sunny, I take the XJ 4 miles to the Interstate at 20-40mph, drive about 10 miles northbound at 65mph with the A/C on, turnaround and drive southbound without the A/C, and then the 4 miles to home. Under these circumstances, the stroker loves 221-235ºF.

In the below timeline of events and contrary to forum posts, you'll see that hood spacers did nothing as did the HD/ZJ fan clutch in terms of lowering coolant temperatures. My Mopar HD radiator is six years old and made a big difference right when I installed it with the 4.0L. I'm currently unsure if it's as effective today as it was when it was first installed. The IR gun temperature readings of the both hoses show about a 20º drop, but I don't know if that's what it ought to be.

Timeline of events:

• 10/2011 purchased XJ (temps normally at 210-215°F at any OAT and any speed)
• 10/2011 install roof rack
• 12/2011 install winch mount
• 12/2011 install rock sliders
• 10/2014 4.10 gearing
• 8/2015 install K&N CAI
• 8/2015 install Flowmaster 2.25-in cat back
• 9/2015 tow to/from Utah and begin cooling saga
• 2/2016 install Mopar HD tow radiator (2-row aluminum), OEM water pump, OEM 195º thermostat, Napa hoses (no spring) (normally runs at 195°F now without towing and might see 210-220º driving through Utah in 95º+ temps)
• 9/2016 install bigger crossmember/belly pan
• 1/2017 install efan override switch
• 9/2017 install ZJ fan clutch (supposedly heavy duty air flow, but creates more engine load)
  • Found on 9/6/2022 that I bought a standard fan clutch by mistake
• 6/2021 OEM efan failed and was replaced from an AutoZone fan while on the road (don’t know its cfm)
• 8/2021 removed CAI and went back to stock
• 5/2022 stroker with Flowkooler high flow water pump installed
  • installed temperature probe in engine bay on top of the brake booster
  • monitoring engine temperature and intake air temperature (IAT) via OBD2
  • runs hot ~221°F at highway no A/C regardless of outside air temperature (OAT) (including 55ºF); got up to 235° on highway without A/C and 60ºF OAT
  • during install, the radiator and A/C condenser fins were cleaned and straightened. The radiator was also flushed out a few times.
  • noticed the engine running hot before the A/C condenser was reinstalled
• 5/2022 replaced efan with OEM
  • noticeably more airflow than AutoZone fan simply by blowing air in my face prior to install
  • coolant temps seem to have dropped 2-3º
• 5/2022 replaced radiator cap (16lb Stant)
• 5/2022 test drive highway speed in 4th vs 5th all with efan override on (help determine if issue is water flow)
  • 65mph cruise
  • Temp increased in 4th
  • Temp increased with AC on
  • OAT 87°F
  • Water temps
    • 221° with fan on
    • 228-230°F with AC on
    • 217-221° idle and stopped
  • IR gun temps
    • Thermostat housing 218°
    • Upper hose 190-200°
    • Lower hose 176-185°
    • Top of radiator no fan 195°
    • Bottom of radiator no fan 170°
    • Top of radiator with fan 176°
    • Bottom of radiator with fan 115°
    • Water pump housing 176-195°
    • Exhaust header 400-440°
• 6/2022 replaced radiator hoses (Mopar and lower has spring), Robert Shaw 195º thermostat (two changes at once, I know, it goes against what should be done)
  • Takes a really long time to reach 195° — seems to act like a 180° tstat when cold.
  • Highway test seems to be 221° with A/C and 210-212° no A/C
  • Turns out I received a 160° thermostat by mistake
  • Water temps
    • 210° with efan on
    • 221°F with AC on
    • 195-206° idle and stopped
• 6/2022 removed winch
  • no noticeable difference
• 6/2022 Spray radiator and condenser with distilled water until wet (if temp falls then likely radiator or air flow issue. Otherwise water flow problem)
  • 221° idle in garage
  • Sprayed seems to have dropped to 215° without efan
  • Sprayed seems to have dropped to 205° with efan
• 6/16/2022 Mopar 195º thermostat and water pump
  • OAT 88-91°F
  • Water temps
    • 210-215° with fan on
    • 210-224°F with AC on (northbound held 210º and southbound was 215-224º)
    • 213° idle and stopped
• 7/6/2022 Ceramic coated header installed
  • OAT 88-91°F
  • Water temps
    • 222° with fan on
    • 224-228°F with AC on
    • 217° idle and stopped
  • IR gun temps
    • Exhaust header 280-330°
• 7/11/2022 Water wetter
  • OAT 91°F
  • Partial cloud cover
  • Water temps
    • 212° with fan on
    • 206°F with AC on northbound, 217° with AC on southbound
    • 213° idle and stopped with AC
  • Air temps
    • 125° IAT northbound, 157° southbound
    • 130° engine bay northbound, 145° southbound
• 8/5/2022 Replaced coolant with Redline Supercool
  • OAT 88-91°F
  • No clouds
  • Water temps
    • 221° with fan on southbound
    • 226°F with AC on northbound
    • 203° with heater and 20-40mph
  • Air temps
    • 138° IAT northbound, 140° southbound
    • 149° engine bay northbound, 145° southbound
• 8/12/2022 3/4” hood spacer
  • OAT 91-93°F
  • No clouds
  • Water temps
    • 230°F with AC on southbound
    • 212° with heater and 20-40mph
  • Air temps
    • 145° IAT southbound
    • 147° engine bay southbound
    • 170° IAT stopped
• 8/13/2022 Borla muffler installed and hood spacer removed
  • OAT 83-93°F
  • Mostly sunny
  • Water temps
    • 225°F with AC on northbound
    • 225° with fan on southbound
  • Air temps
    • 129° IAT northbound, 130° southbound
    • 139° engine bay northbound, 140° southbound
    • 150° IAT stopped
• No thermostat
  • 65mph cruise
  • OAT 93°F
  • No clouds
  • IR gun temps
    • Thermostat housing 218°
    • Upper hose 185°
    • Lower hose 168°
  • Water temps
    • 221°F with AC on northbound
• 9/7/2022 Installed HD/ZJ fan clutch
  • No thermostat
  • OAT 91°F
  • No clouds
  • Water temps
    • 221° with fan on southbound, 230° with AC southbound
    • 221°F with AC on northbound
    • 215° with heater and 20-40mph
  • Air temps
    • 138° IAT northbound, 140° southbound
    • 147° engine bay northbound, 145° southbound

I think I'd like to go back to Prestone coolant/antifreeze + WaterWetter as I think that combo worked a bit better than Supercool does. I'm on the fence about replacing the radiator as I haven't been able to prove it's the problem just yet. Most people say the discontinued Mopar HD radiator that I currently have is the best. Lots of folks said the discontinued Griffin radiator fixed their cooling problems. The remaining all-aluminum radiators seem to all have mixed reviews and some spring leaks prematurely (Cold Case, Mishimoto). Once I decide to replace the radiator, it'll likely be the Champion BC1193 (unless I'm talked into something else like a single row radiator). But I don't want to throw big money just to try parts without proving I'll get great gains. Do you have any ideas of better methods to rule in or out the radiator as being the issue?

There are also great debates on whether high flow water pumps, thermostats, and thermostat housings work better or worse. I don't think the high flow Flowkooler water pump worked well in my case nor am I convinced more water flow is the answer if my hose temperature difference is only 20º when I got the coolant temperature up to 221º and that's without a thermostat.

I also would like to see how much an oil cooler would help (https://www.summitracing.com/parts/der-15660) once I figure out where to put it as I think that could net decent gains.

The thing runs fine when the OAT is below 80º. It just can't handle the hot summer air (and neither can I).

Update 2022-10-01: HD/ZJ fan clutch doesn't help.

Update 2023-04-11: Champion BC1193 radiator significantly helped.

awg

try running down the highway with the heater on max.

if this helps, thats suggests a problem with the radiator

my running temps dropped significantly when I recently replaced my radiator (it had a pinhole)

I used a stock style rad, as they are cheap ,relatively reliable, and fit

Its winter here atm, will see how it goes with summer temps, which reach over 100F

WillyXJ

Interesting thought. I hadn’t run my usual test route with the heater on the entire time. I’ve had it on when coming home which dropped the temps some. But I’ve also recently had it on while going up a high-altitude pass at 55mph in third gear and had to pull over as the temp got up to 240° which is my limit. We’re nearing the end of summer which means I’ll be running out of those hot days soon, but I can run that test in a few days once this cold front passes. Thanks.

cruiser54

Have you ever tested that new radiator cap?
Does the cap have one of those release levers?

nowhereman98

If your profile picture is accurate, try removing your winch. It looks like it is blocking a good portion of the grill. Otherwise I would look at replacing the radiator.

WillyXJ

I did not formally test it. But it seemed to have performed the same as the Mopar one it replaced. It does not have a release lever, but when the coolant was still warm, I did unscrew it a bit and pressure was released.

I did remove the winch back in 6/2022 and it made no difference. What leads you to think it’s the radiator so we’re not shotgunning?

cruiser54

what if that pressure is 6 or 7 pounds and not 16? Just a thought.

And yes, your winch blocks a lot of the grille.

tech

I've been looking at the XJ's cooling system and what I see is that the radiator is short and long it should be a taller radiator but that would take cutting the frame up front . the other thing I see is that belt driven fan blades are cut near the ends that do the most work and the fan shroud does not cover the fan properly . I've been looking for a newer belt driven fan like some cars have a 8 or 10 blade fan and most are phasic and I would make a fan shroud to fit and it would pull a lot more air though the radiator . the other thing some do is cut the hood and install louvers to let out the heat .

Jim Malcolm

Put a thermostat in the system. It is required to allow pressure to build in head.

Go back to regular ol' anti-freeze and water. None of the non-water-based coolants cool as good.

Those temperatures you had on 7/11 don't look too bad...

WillyXJ

Interesting point about the pressure. I’ll see about getting that tested. Thanks. The winch may visually block some grill, but I’ve driven with and without it (longer than just a test drive, too) and there was no difference in cooling so it doesn’t seem to block any airflow.

Yes, I plan to put a thermostat back in. It was taken out for testing. This is the first I’ve heard that it builds pressure in the head — it’s been my understanding that heat builds the pressure. Can you elaborate on your comment?

Jim Malcolm

"Allowing pressure to build" is somewhat different than building pressure. As you state, adding heat to the system will cause pressure to build, but only if it's a closed system. A pot of boiling water on a stove doesn't create pressure since it's not closed.

While the cooling system on a Jeep 4.0 is closed as a whole, that doesn't mean that the pressure is the same throughout the system. The radiator cap limits only the pressure in the cold side of the radiator. By inserting a restriction, such as a thermostat between the radiator and the engine, higher pressure will be achieved in the engine, allowing the coolant to accept more heat before vaporizing. Once up to temperature, this is the primary means by which the engine is cooled. Tiny bubbles of steam are developed due to the large difference in temperature between the engine and the coolant. The movement of the coolant caused by the water pump pushes the bubbles away, allowing colder fluid to takes its place. The steam bubbles then recombine back into the fluid. As stated, the thermostat increases the pressure level that can build in the engine, increasing the efficiency of the heat transfer.

While we're on the subject, pull up a picture of a water pump for a small block chevy once. What you'll see is an actual pump, with an inlet and an outlet. Now look at the "pump" for a Jeep 4.0; it's more like a fan than a pump. I worked with multiple Powertrain Engineers who design cooling systems daily and all agreed after I showed it to them that the "pump" on a Jeep 4.0 is really just a fan, keeping the water moving inside the engine, preventing steam pockets from forming. The Jeep 4.0 style of pump is not capable of generating any significant pressure, so the effect of the thermostat as a pressure generator plays an even bigger part than most engines you read about...

WillyXJ

Thanks for the explanation, Jim. In my head that pressure would exist until the thermostat is wide open. Isn’t a wide-open thermostat essentially the same as not having one? Seems to me any time the coolant temperature is higher than the thermostat’s rating, it’s no longer performing any function since it’s wide open and no longer regulating. But perhaps it’s still allowing that pressure since the opening in the thermostat is still smaller than without a thermostat.

Jim Malcolm

Compared to the full pipe diameter, just that perimeter opening of the valve itself makes quite a difference. At least enough of a difference for it to matter... :-)

WillyXJ

I agree 7/11 had the best test results and I was excited that day about it. But after driving with that setup for a while, I noticed the temps would still get up in the 220°+ range. I realized the test was conducted in partly cloudy conditions which I paid more attention to later. 90° and cloud cover is significantly different than 90° and sunshine. I plan to test the radiator cap, install the thermostat, and go back to that coolant combo this week. If the forecast holds, I should have a day or two for another test to see the impact.

I’m still looking for something to make a 10° or better impact. Ideally, the thermostat should be regulating the temperature rather than outside conditions, but we may never get there with this cooling system design.

Jim Malcolm

Time for a new radiator. Works every time....