After doing a lot of reading on various forums regarding Jeep 4.0L coolant loss & cracked "0331" Cylinder Heads, I put together a summary of the key info. Thanks to all who've shared a lot of useful info!
2000-2001 Jeep Cracked Cylinder Head
Cylinder Head Casting # 0331 (stamped on Driver's Side at top, middle at valve cover edge. Used from 2000-2001
NOTE: "0331" used a mounting boss for the Coil Pack. Switching to an earlier Head ("0630") will require special brackets to Valve Cover to support Coil Pack.
In 2002/2003, Jeep switched to a different casting ("TUPY") from Brazil. Supposed to be stronger, better than "0331" '99-'04 Grand Cherokees's use "0331".
"TUPY" casting is visible through Oil Fill Cap, looking straight down at Head
SYMPTOM:
Unexplained coolant loss.
Oil pressure may go down after starting, warming up.
No heat; Low coolant.
Poor idle; Misfire. Check Engine Light.
CAUSE:
Overheating, lack of maintenance, low coolant. Check coolant, hoses, fan, thermostat often. Flush Cooling system regularly.
EVIDENCE OF COOLANT IN OIL:
1) Oil Sample Test-
http://www.blackstone-labs.com/ $20. High in iron (292 ppm, normal being 65) indicates Bearing wear.
3) Pressure Test w/Valve Cover off; coolant will appear at crack between #3 & #4 cylinder.
4) Run engine w/Radiator Cap off- Bubble indicate coolant in combustion chamber.
5) Coolant level going down, oil level going up.
6) Milky substance in Oil Fill Cap or Radiator Cap.
7) Drop in Oil Pressure. (50psi at start, goes down to 10psi when warmed up). 13-20psi at hot idle, 60psi @ 2500rpm. Running Temp: 210
Coolant in the oil will cause deterioration of bearings indicated by a drop in oil pressure. If your compression is still consistent & strong on all cylinders (120+), bearings are ok.
LOCATION OF CRACK:
Under valve cover, between valve springs of cyl.#3 and #4. Sometimes visible looking through Oil Fill Cap. May not see crack but will see crusts of coolant (brown/green).
Also look for creamy-brown emulsion inside crankcase (evidence of coolant mising with oil). If crack is into exhaust, coolant will burn off through tailpipe. If crack is into combustion chamber,
coolant will cause damage to Cam, Main, Rod Bearings. Also may cause gunk/build-up in oil pan and Oil Pump & Pick-Up.
If the crack is between an intake port and the water jacket (or between the combustion chamber and water jacket), the engine might run like it's on 5 cylinders.
Check the plugs and if one of them has less carbon than the others with traces of coolant, you'll know which cylinder is affected.
Most "0331" heads are cracking on the valve spring side (which won't cause a miss).
If it's between an exhaust port and the water jacket, you'll have steam coming from the exhaust but the engine will run fine.
If the crack is only between the water jacket and the crankcase, you'll only have the mystery loss of coolant with the engine otherwise running well.
SOLUTIONS:
1) Addititves to fill crack are not recommended and won't last. Plus, they will only further gunk-up your engine.
2) Use an earlier casting ("0630") from '95-'99. Will also need matching exaust manifold (or adapter), head bolts, head gasket set, custom down pipe and O2 wiring extensions.
The "0630" Heads have smaller ports and do not have retainers for Coil Pack as used on '00-'01.
3) Use a later style Head ("TUPY"). 2002/2003 and up.
4) Aftermarket Head- Alabama Cylinder Heads (800-235-4323)- $510 includes shpg....Currently 75+ back-orders. New, thicker casting in weaker areas.
5) Clearwater Cylinder Heads (800-572-1963)- $455 includes core exchange & shpg. (in stock)
6) J&C Enterprises (800-266-5599)- $439 includes core exhange & shpg.
REPAIR NOTES:
- Coolant in Oil: Replace Cam, Main, Rod Bearings + Oil Pump & Sump.
- Coolant through Exhaust: Flush system, use new FelPro Head Bolts, FelPro Gasket set
- Typical repair shop labor to replace Head: $700+
