Hi,

This is my car: 1987 300D Turbo. 186.5k
miles, starts instantly, runs 2 mm above the
80 degree mark under normal driving. 27
MPG mixed driving.

This is the problem: I hear one heck of a racket coming from my engine under the following conditions:

* Start cold, let idle until warm. Slight
noise that gradually gets louder.
* Idle or drive in stop and go traffic.
Power feels fine, but I don't know if it
is less than what I should be getting.
When I floored it getting on a freeway
onramp with this noise it would not rev
much above 3000 RPM and took longer to get
to 65 MPH. Normally it revs to 4000 before
shifting.

The noise can be eliminated when I:

* Shutting off the engine
* Coast in 3rd gear at 50 MPH down about 2
miles of hill. During this time coolant
temp drops to 80 due to the cool breeze
and minimal throttle.
* Take it out on the highway. Noise is gone
by the time I reach the top.

The noise is a "tick-CLACK" repeating about
3 times per second at idle and faster at
road speed. It is very slightly
distinguishable from inside the cabin. About
as loud as someone's voice when standing
outside the vehicle, and very loud with the
hood open.

Although I'm not sure, the noise at idle
seems to go coincide with oil pressure
just a shade under 2 bar. When there is
no sound it's usually right at 2 bar.

The oil is Pennzoil 20w-50 changed 1200
miles ago by Mercedes Recycling in
Watsonville, CA. I've told by some very
helpful people on the Internet that it
isn't quite the right viscocity of oil to
use on the diesel. I bought a quart at
the store for backup and later noticed
that there is no suggestion
of a CF, CD, etc raiting on the container,
so I guess that it's not designed for diesel use. The mechanic there wanted to replace
all my lifters, but I declined since the noise wasn't happening very often. Now, 1200 miles since having the oil changed, it has become more prominent.

I recently took it up to 4500-5000 RPM in
2nd gear on some hills because of this noise, in hope of cleaning everything out. Instead the car started leaving pools of oil wherever I parked it, especially on inclines. I may have caused a lot of oil to leak from somewhere and pool in the sound cover under the engine where it is dropped when I park the car. Oil level went down 2-3 mm on the dipstick after this. Transmission now seems to shift more firmly (yay!) but the clacking
noise now comes more often and is louder. Exhaust smells and looks the same, although I have an oxidation catalyst.

What I'm unclear on is whether using that non
diesel rated oil at that viscosity can cause
that specific sort of problem. Pictures
are available at http://max.jrd.com/merc where you can see the dipstick on each side (1 and 2) when first pulling it out (before) and after wiping it and reinserting it (after). Based on afterwiping1.jpg, it appears as if the oil level is halfway between Min and Max, yet there is oil coating the entire other side of the dipstick between Min and Max. What is the real oil level here? Does the oil appear to be thinned out, is this how it should look, or is it possible to tell? (This is on a cold engine.)

Will Marvel Mystery Oil and a fresh dose
of 15w-40 diesel rated oil solve this problem? Is this oil leak possibly a sign that air is getting back into the oil? It seems unlikely, considering that the oil is supposed to be under pressure. Is the non diesel rated oil causing carbon buildup or thinning of the oil? The oil pressure used to hold at 2 instead of dropping to just under 2 at warm idle... after my "italian tuneup" it is slightly lower than it used to be.

In any event, this noise doesn't sound like it can be very good. Is this noise damaging to the engine, or can I just ignore it? It doesn't make economic sense to change the oil after only 1200 miles. (I would get it done at a different independent shop that uses higher quality oil, and my last oil change at Merc. Rec. was $60) If I provide a Bosch filter, is it safe to take it to a "quick lube" place closer to home than a mechanic?

I don't believe it is injector noise. I floor it regularly and put a dose of STP in a fresh tank not long ago. It seems as if injectors would be a different sort of noise and at different times. I will try to have a WAV file available of the noise sometime tomorrow at the above URL. The noise sounds like it's coming from the center point between the front end and back end of the valve cover. I can't hear a difference in volume when I take off the oil filler cap. When I remove the filler cap there is a little oil splashed up and down and I can see the metal on the moving parts through a jacket of oil.

All thoughts on this matter will be greatly appreciated. Please feel free to browse the files at the URL I posted. (Keep the hood star pic if you like it!) I've heard there
has been an update on the lifter design
but I do not know whether the car has this
update (I've had it for 5000 miles and do not
currently have past service records.)

Thanks in advance, and happy new year!
Justin