1994 Ford Explorer Rattling noise from engine (not alvays)

If you are sure it is in the engine, it could be many things. Remember, unlike water, steel expands when it gets hot and shrinks when cold. Thus, if you have a worn bearing, lifter, rocker, wrist pin... when it is cold you may hear it, but when it gets hot and the steel expands, the sound may go away. With this many miles on it, the only way to be sure is to take the engine apart and check clearances, wrist pins...

Make sure it is in the engine and not something like a heat shield, water pump...

Let me know if you have other questions.

I'm sure that is engine noise. But I'm not very happy to open ,otherwise perfectly working engine with full power and torque, for checking and measurement. I'm driving with that occasionally noise more than 30.000 km, and situation is not any worse. (perhaps and more km because when radio is on you can not practically hear that, it so quiet. Of course that I now hear that noise in background, once when I already know when it come and how it sound). Noise on cold engine first time appears in occasion when I don't drive vehicle for three weeks and after approx. one minute working after first start (in cold late autumn day) noise appear. When engine is wormed it disappear. From that time I already change type of motor oil from Valvoline Syn power 5w40 to Motorcraft Formula E (now F) 5w30
and maybe have little benefit but I'm not sure

An again, when I need power or when engine is under load noise is not there, I'm sure.No mater of rev's.

I have already hear about some cold engine lifter problem.
And only thing what I change so far to engine is thermostat, spark plugs twice and spark wire once.
My engine is running mostly on LPG but noise is same on petrol or LPG.

Sorry ,maybe I wrote to long but I try to pinpoint problem

Hi:
I agree with you not wanting to take the engine apart, and I understand why. It is hard for me to tell 100% without actually being there to hear it. However, as I explained, a cold engine is more likely to make noise than a warm one. Thus, I feel that it is a bearing. Have you ever tried any additives with the oil when you have it changed?

I never put any additives in engine oil, only MoS2 paste from Liqui Molly in gearbox.
When I try to pinpoint the location of noise I inspect all engine with stethoscope , and find some different noise from first cylinder(front driver side), something like very very slightly knocking, but cylinder balance test don't show difference btw cylinders, so I concluded that is normal wear to bearing or cylinder according to mileage, for front cylinder, which is alway in stream of cold air from fan. In my experience, always cylinder which is next to the fan (eg. straight six engine) wear much more than others.But that is not the noise which I'm looking for
In my case noise came from passenger side of engine, and thing what is most wondering is why disappear when engine is under load?Like something is going loose and knocking when you stop to load engine around 3000 rev. Is it possible to be something with timing chain or tensioner for it?

It could be a worn timing chain, but they usually don't make a knocking sound.