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:
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
- 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