Soo tonight as I was driving home I stopped at a restaurant to pick up my dinner while my boyfriend sat in the jeep and left it idleing.

Walked back outside and this happened...
1. Jeep smoking
2. Coolant Reservoir Bubbling. Literally bubbling.
3. Severe hissing noise.

The engine was not overheating.
There is low oil(at the point where it curves at the bottom)
No milky oil
The coolant was a light grey color, not sure if that was just the smoke from being in there but it definitly was not green!!
Its a 2000 Jeep XJ straight 6. 4.0L only 150k miles...

The only issue I really have right now Is a cylinder 3 misfire which causes the dreaded Heat Soak.

Please help?

 

It sounds like your head might be cracked. open the oil fill cap and look down if you see any sludge on the bottom of the cap or a visible crack between cylinders 3 and 4. don't drive it till this gets fixed. if there is no coolant in the oil right now you may have lucked out and the lower end of the motor may still be alright.

 

A compression test will tell if you have a problem or not.

 

Took it in to the mechanic, the Camshaft Position Sensor that caused the issue as well as my secondary fan decided to completely stop working too. Need to go to a pick and pull for a new fan but I did replace the Sensor and the jeep is running like a champ. My Check Engine Light is even off too!

 

The fan is less that $60 on amazon. Just replaced mine. Significantly quieter than the factory fan too.

 

Aaaaaand another one.

The 2000 XJ came with the notorious 0331 head that had a casting flaw that causes some of them to crack between the #3 and #4 cylinders. Search the forums for "0331 head crack" and you'll find volumes. Mine did it. Seems like we're getting about one a week on the forums now.

Depending on how it cracks, it can allow hot exhaust gas into the cooling system, which can spew out through the coolant bottle. It also boils the water out of the coolant at the point of the crack and leaves behind a red/brown sludge that sticks to everything, clogs up radiators and heater cores and can eat a water pump in a matter of months. Because of where it is, it can also cause a #3 misfire, but it often doesn't throw a CEL at all.

Sound familiar?

In the old days you could tell if there was coolant in your oil by looking at it for milkiness. That's no longer a reliable test because modern oils have better detergent packages that prevent that milky look but don't prevent destruction of the bearings from contamination. You may not see a clear indication on the dipstick or on the bottom of the oil filler cap.

Because of this and the bulletproof reputation of the older 0630 heads and 4.0L engines, mechanics often misdiagnose the 0331 head crack. Two very experienced mechanics missed mine. It was only a problem for two years at the end of the Cherokee, so it's not surprising that someone who doesn't specialize in Jeeps wouldn't know about it.

Given your symptoms, quick and fairly easy test to "rule in" a head issue is to put a combustion leak tester on the radiator to check for the presence of exhaust gas in your coolant. A test kit costs about $50, but many mechanics have them in their shops. If it tests positive, you have either a cracked head or a blown head gasket.

Regarding your electric fan, people often assume it's not working because of a design change for 2000. Prior to 2000, the electric fan came on when you turned on the air conditioner. Starting in 2000, the fan does NOT automatically come on with the AC. Instead, it comes on when the high side pressure in the AC system hits a certain level or when coolant temperature exceeds 117° F. A lot of people (including experienced mechanics) will turn on the AC on a 2000 or 2001, see the e-fan not turning and assume it's bad. Did your mechanic actually test the fan itself with a resistor? CCKen provided some excellent info on that here.

Also, can a CPS cause boiling coolant? That sounds a little suspect to me. I think you may need to take your machine to someone else for a second opinion.

There's always a possibility that your head is not cracked. However, given your symptoms and the propensity of the 0331 to crack even when properly maintained, you really ought to rule it out before throwing a bunch of money at a mechanic to replace a bunch of stuff that isn't bad.

 

$25
http://www.blackstone-labs.com/

 

Combustion leak tester as per extrashaky post.
http://www.napaonline.com/Catalog/Ca...006_0361073538

A leak down test will show either a cracked cylinder head/engine block or a blown head gasket. A compression test is too general a test, ie. piston ring worn, valve not seating, etc.