Constant Ticking Valve M103 motor
 

Before I begin, I've seen a few threads with similar issues but I haven't really got my issue answered.

1988 Mercedes 300CE with 172,xxx miles.
- Oil changed every 3,000 miles with Rotella 15w-40.

When I first bought the car, it had no valve tick at all (162,xxx miles). I moved across country and drove her 2,600 miles with no issues. It always had a rear tick sound for a couple seconds as soon as it cold started after sitting for a good 12 hours.

Last month, I started trucking and left the car sitting for 4 weeks. I came home, put some fresh gas in it and it cranked up immediately but had some hesitation so I revved it to keep it running. I accidentally revved it to 3,000 rpm as soon as I cranked it and it started ticking constantly. It's not a loud tick and it actually is a very quiet tick. I know these cars have hydraulic lifters so they can't be adjusted. I've also read that replacing 1 quart of oil with auto trans fluid for a 500 mile cycle can "unstick" any "stuck" lifters. Revving it that high was a mistake I think caused the issue. Hopefully it's nothing major or I'd probably have to sell the car due to going into college for a 2nd time and can't have huge car expenses in the near future.

- Any advice on fixing the issue or things I should look at would be great. I've read on Pelican Part forum that a nice "highway blast" can fix the issue as well. Other than the tick sound, the car runs fantastic!

Any other info. needed I can give.

Thanks,
Jonathan

Remove your valve cover and inspect your camshaft and rockers immediately. M103s prior to 1989 had the infamous soft cam. I have a 1988 300ce and it happened to me - camshaft wore out early - similar ticking noises especially over cylinders 1 & 2

Another possibility would be a worn lifter...it fits this scenario.

Don't do this. (Used car lot myth/old wives tale.) A worn/leaking lifter is worn & leaking internally, not 'stuck'. All you are doing with ATF in the oil is risking more damage. (ATF is 'high detergent' so it may help loosen/move sludge - but really, is that a good idea on an older engine? Or asking for trouble?)

Yank the valve cover, check for loose rocker, if all snug have helper crank engine watching the rockers for the one not moving like the rest - that's the bad hole.

Good luck.

Thanks for the replies guys. The tick has gotten quiet over the past few days of driving it since being home. I'm not sure if that means something else or not.

When checking the rocker arms, is there anything else I need to check for while inspecting the rocker arms? Is replacing those pretty difficult at all? I've done it on a Japanese 4 cylinder once.

And to add, idle seems to be a bit hard/shaky, the motor seems to be burning a tad bit of oil and/or getting too hot to disperse it. The oil light will come on after driving around 2,000-2,500rpm (highway driving) for 25-30 minutes. That's probably a completely different situation though. Anyone have the diagram of the oil coolers on the M103?
Thanks again,
Jonathan

I would think the ticking getting quieter is a good sign. Its possible it was just sticking from sitting for a few weeks and its loosening up with use. The oil light could be any number of items. I know you think its burning oil but is the level dropping or is there any evidence of it leaking? The oil level sensor on these cars can fail but the symptoms are usually different.

When the oil light comes on, I'll stop and check the oil level (obviously the car is at hot running temp. at the time.) Seems to be at a lower reading mark than when checking it at cold. But that will be normal. I do add a few drops of oil and the oil light will go away. Also, once the car sits for a while and gets cold again, the oil light will not light up. I don't see any leaking oil anywhere. Hence why I was wondering about the oil cooler question and thinking about installing a front mount oil cooler.

Another question: Is there a way to tell if the previous owner(s) replaced the pre '89 cam with a newer M103 cam?

depending on your climate you may need to run 10w40 oil.I run 15w40 in my m104 which shares same block,but in colder months run rotella 5w40 sync.

Take the valve cover off and take a good look for any broken valve springs. I had a broken spring that I found during a head gasket change..not sure how long it was like that, but my "tick" I had stopped so it must have been that.