First of all, long time reader, first time poster. Love the forum and have found tons of info here over the last two years. I have a 1992 300d with 212k. I've owned it since 150K and put a little over 60K on it in last two years. Has always run great. It has also always been a noisy engine but lately I've begun to suspect it may be noisier than normal. The body and interior are in great shape and I really hope to drive this thing to 300k plus so if there is something wrong, I'd like to get it diagnosed ASAP.

Did some quick research on knocking or nailing on this forum and came away with some pretty terrible feeling of foreboding and doom... hopefully its not headed this way.

I took a video of the car at idle. Here is the link. Any thoughts?

1992 300D engine at idle, knocking, or normal? - YouTube

It doesn't seem to use oil. I do all recommended maintenance myself. Just changed fuel filters yesterday. There does seem to be an oil leak somewhere as I notice oil periodically below the inline filter on the engine. I shot the location of that at the very end of the video but it is difficult to make out.

I will most likely take the car to the same diesel mechanic that has worked on it for the last decade for a checkup but it would be nice to know if you guys think that is warranted.

I did a blowby test, no noticeable smoke/steam but there was some oil being tossed/sloshed around a bit out of the filler hole. That normal?

Thanks all for any insight.

Ryan G.

Sounds like tapping hydraulic lifters to me...common around that mileage. Does it ever go away? Does it go away above idle/warmed up? My OM601 taps when cold for a couple miles but it goes away at operating temp. Generally the only "fix" is to have them replaced.

Oil sloshing out with the cap open is normal.

Tapping can also be from the front belt tensioner assembly but it sounds more like lifters to me from the video....

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Thanks for the reply. It does seem to be an issue primarily at idle. When driving I find the engines smooths out and sounds very tight as soon as I get into motion.

What's a job like that run with a good indie diesel mechanic usually? Figure i'll take her over and have it looked at... i love this car too much to do otherwise. i've heard motor mounts, and lifters as well. Suppose thats better than a rod knocking.

Gonna do a diesel purge this week when I have time. If the noise were to lessen/disappear when doing so, what exactly would that indicate, injectors?

Ryan

Just drive it. If it goes BANG you found the problem ! As a fiscal matter, engines of this age are cheaper than an overhaul. Come to that, so are those vehicles.

The audio on your video is not definitive enough. Sounds fairly normal. Loose/worn belt tensioner bushes ?

If you think it's lifters...pull the valve cover and look with it idling. I have seen several with lifter/cam wear that went on for years.

FYI : I believe you should never get emotionally attached to a machine.


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I had a similar sound resonating from the front center of the engine on my 82 300D at idle only. If I had to describe it, I would say that it sounded eerily reminiscent of the sound associated with a ball bearing being tossed around the inside of a can of spray paint while shaking it. To make a long story short, it ended up being a bad fan clutch. I am not familiar with your engine, but if you wanted to check to see if it is indeed the fan clutch, simply unbolt it from the water pump and run the engine for a few seconds. If it is the fan clutch, you will notice that the sound has ceased immediately.

Good luck figuring it out,

Drew

Much easier said than done! I venture these forums wouldn't be so crowded if merc diesels didn't have the tendency to provoke attachment.

I think the fan clutch is also noisy actually so this would be a good way to figure out how much of the noise originates there.

In reality, I don't mind it being noisy, I just don't want it to go BANG as dkveuro says. So if I can at least determine it isn't terminal I'll be a happy camper.

It sounds a little bit like the belt tensioner as mentioned above. Very carefully (fan blade is close) push your thumb on the top of the belt tensioner shock and see if its changes the sound.

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1995 E300 Diesel