Hello,

I am working on my neighbor's 91 300CE again. It has the DOHC 24V M104 engine. Recently it developed a horrible sounding clatter. When she started it, the car had been sitting for not more than a day, it's a daily driver. When it started, loud upper engine noise was obvious. I made her turn it off quickly, so I don't know whether the noise lessened after the oil pressure pumped up the lifters.

I advised her not to drive it. Today I took the valve cover off and checked some of the lifters that were not being pressed down by the cam. Some of the lifters went down pretty easily and made a light clacking sound as they bottomed out. Others felt more resistant, but could still be pressed down all the way. All of the ones I checked returned back up after pressing. The engine has about 150,000 or more, not really sure but the car has not been carefully looked after. It has some rough edges but it was running good. I worked on it last summer to replace a leaking hose under the intake, and she was driving it daily since then.

I'm looking for advice from those that have been there. What should I replace, how far should I go? Do you think the lifters should all be replaced together? Kind of expensive, looks like 24 lifters x $20 each. I am also hesitant to go any further, since I don't want to open a can of worms. Better to let a shop do it for her? She is paranoid about getting ripped off.

I'm thinking about trying some different oil. She is careful to keep it changed, but I'm not sure what viscosity it has. I have had pretty good results with 15-40 Delo on my 190E. It had some noises that have lessened since I owned it, and it seemed affected by oil type.

Thanks for all your time, I greatly appreciate it. I have gleaned much knowledge here. I have done some searching, but not sure if I have found the right answers on this type of noise.