OK, just looked in again and saw some coolant under the oil cap. I have some questions that I haven't seen answered elsewhere that I'm just curious about. Don't really know much about Jeeps (or cars in general) and trying to learn a little here:
1. Why is it so certainly a cracked head and not necessarily blown head gasket? Seems the symptoms would be similar.
2. Why no overheating?
3. Why no chocolate milk on the dipstick?
4. About how much should installation of the new head cost?
5. What else should be done while the head is off? New head gasket, thermostat...anything else?
6. I'm going to have to drive it out of the city 30-40 miles to get it worked on. Anything I should do beforehand to prevent further damage?
7. How do the Jeeps generally fare after replacing the head? I have no idea how long it's been driven like this since I just bought it, so the vehicle history is not really clear to me. Hoping it can still last a while though, especially with this immediate investment I'm going to have to put in.
1. 2000-01 had a casting defect in the head leading to a tendency to crack if overheated. Again run a search on 0331 head for more info, on top of this 4.0Ls aren't known for blowing head gaskets. This defect was corrected in 2002 so an 02+ head from a WJ (GrandCherokee) or TJ (Wrangler) is an acceptable replacement, or go with buildin1XJ's suggestion of Clearwater cylinder heads, these are even better but of course cost more than a junk yard head.
2. If the crack is small and there is still coolant in the cooling system, it may not overheat, you likely caught it at a good time before it did any real damage.
3. see #2 it takes allot of coolant to make 6qts. of oil milky, but the oil cap being on the head is exposed directly to the area where the oil/coolant mix is occurring.
4. At a shop about $500 + the cost of the head, if you choose to do it yourself it is not that difficult but is time consuming (budget at least a day if you've never done it before).
5.Gasket (head, valve cover, and intake/exhaust of course), Thermostat, rad hoses, might as well do the water pump while you're at it, and make sure the whole system is thoroughly flushed, if the radiator is plugged with crud or leaking have it replaced as well.
6.Change the oil, just use cheap oil and change/have it changed after the head is replaced, it is unlikely enough coolant will leak into fresh oil to contaminate it to the point where it can no longer protect the bearings in 30-40 mi.
7. As long as there is no bearing damage and you use a good head (not another 2000-01 0331) you should be fine, the 4.0L I6 is extremely reliable for the most part, but the 0331 head in 2000-01 is a known issue, a crack usually occurs after an overheat and you never know if a used vehicle has been overheated. It can also take a long time after the crack has occurred for the symptoms to occur, it starts as a tiny stress fracture and continues to grow over time.