87 300sdl 3.0 Tapping Noise
 

I hear a metal tapping noise dead center on top of engine. I opened oil fill cap but could not hear it any louder. The tap makes 7-8 taps seemingly in time with the engine, then stops briefly 1 maybe 2 seconds then taps 7-8. This pattern continues consistently. The cooling temperature is fine, and oil pressure is fine. However, I had just changed the oil and filter 3 days ago. Before this there had been no sound. 286k on motor it had been running great. I've been running 100miles at 70 getting 30/gal. Any tests or repair suggestions will be appreciated. You all have been a great help in the past thanks!!

so far no comments. Should I add some other details?

Switch to Mobil 1 synthetic oil 15w40 15w50.

My 87 300SDL does it every once in a great while too.
I do not believe it's anything to worry about.

Its probably a lifter.

A lifter would not have a consistent repetitive pattern.

yeah. I thought I would hear it louder thru the oil fill opening too! I had tried to hold down any fuel lines or other potentially loose parts but none have solved the problem.

It's the end of the day for me guys. thanks for your input.

strange the lifters on my W124 tend to tap in a pattern when i have a cold start, but eventually clear up within minutes.

What kind of pattern?

Pull the valvecover and crank it over and see what happens (oil will go everywhere, be prepared).

If you keep the rpm's constat they are consistant. But I may have forgotten I replaced mine years ago.

Bad Injector?
 

My 87 300D had a "tapping" or nailing noise. Sometimes it is hard to differentiate the two. I eventually trace it to a bad injector. Replacing it solves the problem.

My 92 300D 2.5 Turbo does it when I drive it hard, leaving for work in the morning its fine, 45 minute run on the highway and I get to work and it sounds like a sewing machines, have replaced all 10 lifters and done some oil treatment but no improvement. I have been using Quaker State 15w40 HDX fleet diesel oil.

Don't know what to do anymore, MB is recommending a valve job which is kind of a minor engine rebuild. The car has only 65000 miles!

If you changed the oil a few days ago, I think in your case its just bad oil that engine is not liking.

Good luck...

Atif

Pretty likely to be a lifter. Try 15W-50 Mobil-1 for a couple thousand miles, if that doesn't help, test & replace the faulty lifter(s).

Atif, try the Mobil-1 on your car... with new lifters it should be quiet. No oil treatment of any kind should be needed. I've heard of more than one car that had the noise go away simply by switching to M-1. (15W-50. Did I mention 15W-50?)

:)

The reason that I conclude that it cannot be a lifter is the pattern 7-8 taps in succession followed by a two second delay..........repetitive.

Sorry, but a lifter cannot be that brilliant.

I'm more inclined to think something on the chain is hitting a stationary object in some fashion.

This would be even more convincing if the "lifter noise" was apparent all the time........never went away under any operating condition.........as lifter noise will typically do.