I have a 2000 WJ 4.7, and I've been noticing lately that whenever I start it up, especially when cold, the engine makes a clicking sound until it has reached operating temperature. I've popped the hood to see if I could figure anything out and I thought it was something on either the fan or belt assembly. Any ideas? Does this happen to anyone else?
Does it have a mechanical fan? It could be the fan clutch rattling. With the engine off, see if you can spin/rattle the fan by hand (as if it's loose).
The other thing would be oil. Are you using the right viscosity (especially for your climate), and is it new or old? Some high mileage engines will begin to "rattle" or "click" when the engine oil is due to be replaced (this is due to worn out parts in the engine itself). This also depends on your local climate. There is a big difference when it's -20* below outside, vs. 40* and raining.
Mine does a slight ticking that I assumed was injector related. It starts ticking and slowly goes into an eight tick cycle with pauses in between the 8 tick cycles.
Never really thought to much about it but now I'm wondering.
Lifters click when cold and worn out.
Wrist pins\piston rings will 'tah tah tah tah tah tah tah' when cold and worn out
Bearings will 'tik tik tik tik tik tik tik' when cold and warn out
Bearings are associated with running hot.
What kind of sound is it? (sounds stupid but every engine issue makes a different sound)
I just had another thought, but sometimes an exhaust leak will sound like a tic or click. You can check your manifolds and collectors / flanges to see if all the bolts are tight. Might also stick your head under the car while it's making the noise.
The noise going away when it warms up is a GOOD SIGN for you. That usually means it's just a leaky exhaust manifold. In my case, my 2004 WJ with 113k on it has this noise all the time and it's more "metallic" for the lack of a better term. Pretty sure I have a bearing about to fail.
**1997 Jeep Cherokee SE**
Former Police Car assigned to 54-26, RIP.