sphinx15

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?

TRCM

Fan clutch ? Does the electric fan on when the engine gets hot as it should ??

Have you verified the electric fan kicks on with the A/C so both fans are pulling air ??

Which temp sensor...on mine, there is 1 for the gage, and another for the fan......


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sphinx15

Has a triple electric fans setup so no fan clutch. All three come on when they're supposed to and seem to pull pretty good.

Unless I'm mistaken the '00 only has one sensor on the thermostat housing.

Bugout4x4

Are they pulling air or pushing air back out the front? This became a known issue awhile back from the factory on those. The loom plug was pinned backwards causing the fans to run in reverse.

sphinx15

Definitely all pulling the right way. I don't know if I totally believe the 3300 cfm they claim but I am getting a decent (I think) temp drop across the radiator.

TRCM

Hmmm...sounds like the electric fans aren't enough.....................

My 96 has one on the temp housing and one on the back of the head, drivers side.

How does your fan setup work ? all 3 always on & speed varies by temp, or does it start more fans as needed ??

sphinx15

All three come on at either a set temp or when the AC is turned on. Right now they come on at around 180-190 degrees.

I'm kinda suspect of the fans too but they seem to do a decent job at idle, but not on the highway. I would think if it were the fans I'd have overheats at idle and be good on the highway.

sphinx15

Anyone know what a normal temperature drop is across the radiator? I'm getting about 40 degrees different between the inlet and outlet hoses.

TRCM

There's a lot less load at idle compared to driving down the road................less load means less heat.....................

Not sure on the temp diff, but would think that would be enough.

How was the coolant system flushed...you or a shop ?


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sphinx15

True, it does seem to stay hot when coasting down hills and such though. But I guess that could be the fans not keeping up.

I did it with one of those radiator flush kits at home, twice, and I had the shop do it since they drained it anyway, though I'm not sure specifically what they did as far as flushing it. In hindsight they weren't the most confidence inspiring operation... In theory it should be pretty darn clean, it was shot cleaned and dipped about 6 months ago before the rebuild.

97Mudpie

If you've replaced the radiator hoses at any time did you make sure the new ones have the anti-suction kink spring or swap one in?

firebane

Hoses don't come with those anymore and you won't be able to buy them either. So either you need to use your old one (if it still exists) or don't run it.

To be honest there is no need to run that spring because if your hose is collapsing you have bigger issues.

sphinx15

Hose is older but spring is still intact and best I can tell not collapsing.

EZEARL

Here is the official word from Gates: ‘’Molded radiator hose construction has been upgraded with more robust compounding and thicker hose walls, this has negated the need for the spring in molded coolant hoses. Originally the spring was inserted @ manufacture to compensate for collapsing.

Also I've replaced many hoses over the years where the coils have rusted to pieces. Guess where too many of the pieces went.

sphinx15

It's a good thought, I'll take a look at it, I was thinking about reverse flushing it this weekend. Anyone ever done something like this http://www.ve-labs.net/electrolysis-...-reverse-flush with the compressed air?