What is a tick, tick, tick sound when idling?
 

On my car, maybe just since it's gotten colder now, I hear a methodical
tick tick tick sound when the car is idling. I wonder if it's stuck valve lifters or something? I've heard this on many MB diesels, so I'm sure it's nothing serious.

Thanks,

Jeff 1991 300d, 112k

You have a OM602? Sounds like bad lifters. Click..click...click..etc.

Is the sound persistent or does it go away as the engine warms up?

Probably lifters. pretty common with the OM60X engines. Are you running synthetic oil?

Most common source of engine noise on the OM60x engines (with single serp. belt) is the belt tensioner. At idle, push on the mechanism with a stick (be VERY CAREFUL - moving parts + wrong move = damage to humans and/or car). If you can make the noise change in anyway, it's time to rebuild the belt tensioner. Usually a new damper is all that is needed, but if the pulley wheel is not exactly in the same plane as the rest of the belt wheels, then you'll need to replace more parts.

After that, lifter noise is also very common and using a good synthetic oil like Mobil1 can cure it (but it sometimes takes thousands of miles of use before it is effective).

Answers to some questions...
 

As to the clicking, it does seem to go away after the engine warms up. Today I was inbetween 2 cars, and I heard it. But I know for a fact once it's warmed up, it's a lot less, or completely gone.

The oil I use is Rotella with soot control.

How would you fix a lifter? And what do they do? Like one person said, change oil and a few thousand miles later it could make a difference. I change the oil every 30,000 miles. Just joking, every 4-5k. Don't know about the previous owner, I bought the car with 89k on it.

Jeff 1991 300d, 112k

I notice mine does it loudly after a period of hard use. I notice it after everytime I run autocross with it, after awhile it goes away.

It's probably lifters. As it warms up it's easier for the oil to get into the ports on the lifters so they start functioning correctly. They eventually reach a point where they tick even when warmed up. How do you fix them? Replace them. That's what I did and my car became shockingly quiet at idle (OK, not really, but compared to before). However, I don't think there's any need to replace them immediately ... if you can tolerate the ticky ticky just let it be. I didn't replace mine until it got extremely annoying and constant. Then I figured, it isn't going to "heal" itself, and considering I got 220k out of the first batch, the next batch would probably be a reasonable investment.

There are other things that could make a ticking sound, but the lifters have a pretty distinct noise. If it isn't a nailing sound, and it's coming from the top of the engine (i.e., not somewhere on the belt drive), it's probably lifters. I think of them as having more of a "ping" sound than the noises other problems might make.

How hard to replace the lifters?
 

I can live without replacing them, but man, I sure wish these diesels would be more quiet at idle and low accelerations. How hard to replace the lifters?

Jeff