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Another XJ Overheat

sphinx15

NAXJA Forum User
Location
Colorado
I know, another XJ overheating thread, but I'm at wit’s end and need some help. A quick bit of backstory, bought the jeep with 80k on it and did have any real issues until about a year ago at 110k. Started with overheating that turned out to be a head gasket. About 10k later the engine seized, no symptoms, no warning. Upon disassembly found the head was badly cracked (0331 casting) and rod bearings were spun.

At this point I decided to go the stroker route. Took the block to a local shop for the machining. Checked it for cracks or damage, got a clean bill of health so went ahead with the machining. Assembled the motor and all seemed well. Fast forward 6 months and 6k miles and I'm overheating and no one seems to be able to figure out why.

So here's what's happening, at idle and around town with the AC off it will run all day no problems, stays between 200-210. At idle with AC on, again no problems. Around town with AC on, good for a while stays right at 210 for about 20 mins then starts to climb about a degree per minute and doesn't stop. Cools down slightly at lights etc. On the highway, climbs at a fairly consistent degree or two per minute until i give up (usually around 240). AC on or off doesn't seem to make any difference and once it's hot it doesn't cool down until I turn it off. If I drive gently around 40mph the temp doesn't climb but it stays at 240. All temps are from an aftermarket digital gauge. Ambient temps don't seem to make a whole lot of difference, most of my testing has been done when it's mid 90’s out but I get the same result when it’s 70. No oil and coolant mixing, no coolant loss.

Engine and relevant Jeep specs:
  • Stock 2000 Jeep 4.0 Block
  • Bored .030”
  • Shot Cleaned & Dipped
  • New Scat 4.2L Crank
  • Icon 4032 Forged Pistons
  • Hastings Moly Rings
  • Clevite Bearings
  • Forged Rods
  • Comp Cams 232 cam
  • Comp Cams Lifters & Pushrods
  • Comp Cams Timing Set
  • High-flow oil pump
  • 24# Injectors
  • Edelbrock Performer Head
  • Stock 00-01 Intake
  • Banks Header
  • Mishimoto 3 Core Alum. Radiator
  • FF Dynamics triple threat fan setup
  • Hood Vents
  • 33’s with 4.56 gears
  • AW4
What I've tried so far (in order):
  • New t-stat, checked water pump: no change
  • Head gasket: no change (cylinder bores looked flawless, no sign of scuffing)
  • Thoroughly flushed cooling system: no change
  • New temp sensor
  • Took it to a shop at this point since I wasn't getting anywhere, they checked fuel trims, O2 sensors, coolant flow, transmission, block test and basically gave everything a once over. Came up with nothing.
  • Was suggested that maybe the cat was blocked causing excess back pressure so I went ahead and did the whole exhaust since it needed it anyway. So 2.5” from the collector back with new cat and muffler, wrapped the header and downpipe while it was out: slightly better in town with the AC on, slightly less change on the Hwy but still a little better.
  • Added separate trans cooler to remove it from the cooling loop: no change, trans runs nice and cool
  • Spaced the AC condenser and radiator out as much as possible: no change in temp rise but slightly better recovery at lights etc.
  • Cowl Intake: no change, still getting intake temps around 150
  • Block test again: negative
  • Tested having the hood vents blocked vs open, with the hood popped, no hood: no change
  • New high flow water pump: no change
  • Wetter Water: no change
I’m not really sure where to go at this point, anyone have any ideas?
 
Will the computer adjust for .030 over or did you flash it? Running to lean can give you heat problems.
 
I've seen a couple threads now on different forums with people having overheating problems with the mishimoto radiator. Swapping to a quality OEM style radiator solved their issues
 
Will the computer adjust for .030 over or did you flash it? Running to lean can give you heat problems.

It's a 4.6 stroker, but the ECU "can" compensate for most things.

OP: I would say your cooling fan set-up!
 
I've seen a couple threads now on different forums with people having overheating problems with the mishimoto radiator. Swapping to a quality OEM style radiator solved their issues

I'm running the Mishimoto new Radiator with no issues. Not running a stroker however. In AZ as well and it has done well for me.
 
What high flow water pump did you install? What t-stat? I fought a mild (was warmer than I wanted, but not overheating) issue and it runs great now. Stock original radiator too.

Does anyone have a part number or description for the "tow package" radiator I have heard about. I heard it's a little thicker than standard?

I don't know what you did for tuning that stroker, but I highly recommend just getting proper tuning from Ryan at flying ryan performance. https://www.frptuning.com/

I would do what others recommended like making sure the condenser and radiator are clean and clear of dirt/debris.
 
you have almost the exact same stroker I do. I had overheating issues as well, and tried a lot of the same things you had mentioned. what ended up fixing mine was the factory 2 core "HD dessert" radiator. Its pricy, but its thick, and with radiators thickness is key. You can have 10 cores, but if the overall thickness is thinner than a single core, then you won't dissipate the heat.

P/n you need is 52080104AC. got mine from Rock auto for around 300$

Old OEM rad is on the left and new OEM HD radiator on the right. notice the thickness difference. another + is this rad drops right in with no fitment issues.

 
close, maybe 3/8" to 1/2". but I also have a oreilly brand clutch that is thicker than the OEM one. With the OEM you would probably have and inch or so.

 
Many good posts already, but Sideways beat me to the main one - FF Dynamics triple fan is your first issue. I was one of the first with their kits, and failed miserably. They now have a note on their website because of me - basically, this isn't going to work in the desert. I prototyped their fan shrouds, no help. It all comes down to CFM, and their electric fans can't cut it. Sure, when the Jeep was in upstate NY in April, it ran fine. Death Valley, not so much.


I've got pages of notes, temperature readings, RPM of fans, etc.Those fans (and really any electric fan that will fit an XJ) just can't pull the CFM needed. I've even talked to Griffin, and they advised against their Spal fan setup.


The radiator seems OK, and it's thin enough to allow the ZJ max cooling fan clutch to fit, along as you have good motor mounts. It's what I am running, and while I don't run cool, I don't overheat.


David Bricker / SYR
 
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