1) engine odor: My 2001 Cherokee has 108k miles and recently noticed a strong engine "smell" when I walk past the front of the Jeep. I can't detect any specific smells (radiator, catalytic converter, etc.) other than a very strong engine odor. I've been checking all fluid levels and don't seem to be losing any fluids. Curious if anyone in the forum has any suggestions as to what the cause might be. Are there any valves that vent into the air if they get plugged?

2) common problems to 2001's with 4.0: I have a radiator thermostat that has started to stick. I planned to replace it myself and checked Youtube for a how to video. I noticed several posts about leaking head gaskets and cracked heads!! I hear a ticking sound at the rear of the engine. It isn't as loud as a clogged hydraulic lifter, but has me wondering. Are leaking head gaskets and cracked heads a common problem with 2001 Jeeps? Could my engine odor be related?

 

I'm at 150k and am experiencing the same thing. All fluids check out, gauges are within the norms. If you figure it out let me know. Maybe you drive an XJ...

 

Update on #1 & 2- opened the hood with engine running and could smell antifreeze. No antifreeze in the overflow reservoir either. Let the engine cool and very low fluid level in the radiator. No wonder my engine temp light started coming on at low speeds. Not a sticking thermostat, but low on antifreeze. I assume fluid was dripping on the hot engine somewhere. Had a local shop do a pressure test on the cooling system which revealed a radiator leak. Had them replace the radiator and thermostat. Everything seems fine now except the motor got hot several times...is this why my "ticking" noise started? I'll do a new post about that.

 

The head cracking on a 2001 is a VERY common thing. If the thermostat and radiator were replaced and it is still overheating, next step would be water pump and fan clutch. May as well do the hoses as well. However, if you are losing coolant without any visible leaks, a cracked head is a possibility. Have you changed your oil recently? If you have, was there any antifreeze/water in it? If you haven't, pull the oil dipstick and see if you can see any antifreeze/water on it.

Pull off the oil filler cap and using a flashlight, check to see if there is a crack between cylinders 3 and 4 (from my understanding, that is the most common place for a crack). I'm not sure about your ticking though.