So at the tail end of a seven hour sprint from the Redwood mountains and down along the California coast with my 300D, I noticed my oil gauge was wiggling around 2, and then upon acceleration would hit its limiter at 3 and vibrate audibly as it settled on 3.
I pulled into a KFC parking lot and tampered with my rack dampener, as its something I have yet to perfect and I know that if its in a bad spot, it causes "loping," which I felt had similar characteristics, but this was not the cause of my vibrating oil gauge, as it did it the whole way home, and then never again.

Luckily in that KFC parking lot I was busy reading while my girlfriend and her sister ordered food. What I discovered, which I had partly already known, but not to this extent, was that obviously as your engine heats up to operating temp, the oil gets looser and thinner, and flows more easily. The big thing I discovered with my 15W 40 Rotella T was that on extended drives, or in higher geographical temperatures, the oil can get extra thin, like REALLY thin. It'll still do its job but it'll flow incredibly fast and easily, which, in the case of mechanical oil gauges like on the 77-85 Diesel W123's, it'll lead to oil surging up and down in the oil gauge tube, creating the appearance of unstable oil pressures and driving you nuts with a loud gauge.

Luckily MB had addressed this and put out a part known as a "Drosselstift," a throttling pin, if you will. This Drosselstift goes *somewhere* in the oil gauge tube and slows the flow of oil to it, to create stability in its reading.

The Drosselstift is German Import and is about $2.15 from my local Hoehn Mercedes Dealership.
Part #: 123 542 00 74

I created this thread to address this Drosselstift Specifically. I have one now, and I have no Idea how to install it. I figured popping the dash cluster out and disconnecting the line would be part of it, but which way does the pointed end face & which section of the oil line does it apply to?

Can someone please shed the final light on this?

Here's the 123 542 00 74 "Drosselstift" pin as it came from the dealership.
I put it next to a dime as a size comparison. No its not rice.
It feels like plastic, and has a groove cut in the side of it that runs its entire length.

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As an experiment, I took the left side of a cluster out of an '83 300D junk car from the pick your part yard. Seen here is the back of the oil gauge on the cluster board. Since the part was so cheap I tried to see if it would fit in the gauge hole, in the name of science. I inserted it pointed-end first and it is never coming out of there. That's why I bought a spare & why I have a practice cluster.

I really need factual instructions on how to install this. Anybody with actual knowledge on this would be a fantastic help. I don't have an (FSM) Full Service Manual yet so I rely on you guys and Dr. Bergsma pretty heavily at the moment. Unfortunately, the necessary info has only been partly covered so far.
So please let me hear from yall on how to finish this installation correctly!

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this is an interesting workaround. restricting the flow seems like it would lessen the oscillations, sure. having done zero research on the matter, the easiest install might be in the tip of the oil line where it enters the filter housing.

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'77 240D, 504H, OM617.952, etc.

Interesting as one of my W123's Diesels has this wildly fluctuating oil gauge at hot idle .

I know many have had the gauge fail and this looks like a simple fix .

FWIW, that ' Drosselstift ' in the Junk Yard gauge should easily come out if you but tap the brass part on a hard surface.....

Same as getting broken keys out of locks ~ it takes a hard rap to jar it loose .

Please let us know if this makes your gauge steady .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

There are three ways to dampen pressure swings with fluids - a snubber, a damper and an oil filled gauge. A snubber is essentially a tiny orifice to restrict the flow of fluid in a sensing line, which is what the drosselstift appears to be. A damper is a device which adds a volume of a compressible element to a sensing line to take up and even out pulses - typically these consist of a diaphragm and an air pocket or spring. And an oil filled gauge uses oil on the movement side of the gauge to dampen the movement of the needle.

Actually there is a fourth way of dampening a fluctuating signal and that is in software, provided the gauge is electronic and not mechanical.

Turns out I needed to use three of these to get a stable (averaged) reading on my fuel pressure gauge when I added that to my gauges project. For my snubber I filled the sensor line with epoxy and then ran a single strand of stranded copper wire through it until it was set leaving a .008 orifice. For my damper I used some closed cell foam in a tube leading to the sensor. And finally in my software I used a rolling average of 100 readings - each time I took a new reading I added it to my set of 100 readings and dropped off the earliest reading.

I have no idea where the drosselstift goes but my guess would be in the line as it goes into the gauge. If so, my further hunch would be that some PO made the all too common error of starting the engine with the cluster out, spitting the drosselstift out of the line.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

I have never heard of this and hope I don't forget about when the issue arises. Thanks for the heads up.

I installed the pin into the oil line on the gauge side of it. I tested the car today and i get normal oil pressure, even with the drosselstift in. I am duplicating this aforementioned trip this august, & ill be going a different route, but the distance will be even greater. I will post my results and a how to when I return. Wish me luck!

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A junkyard is not for junk

Don't know if you checked this, but there is an O-ring on the spindle of the oil filter canister. Not the gasket but rather it sits toward the bottom. When I did my first oil change I found that it was hard and flattened out. I later replaced it. The old one was brittle and cracked like a piece of ceramic when I tried to remove it. After putting in a new O-ring, my oil pressure needle stopped fluctuating. Has to do with the flow of oil going through the filter.

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85 300D 75K Anthracite Grey 0-60 in 13 seconds **For Sale**
84 300D 333K Black (The Velveteen Rabbit) 0-60 in 14 seconds
00 Toyota Sienna 208K (Sold)
15 Subaru Outback 43K
11 Subaru Outback 67K
98 Ford Taurus 100K (Gertie - Was Grandma's - drove it to church and shopping - really) Daughter's car now.
30 Model A Ford 2 Door Sedan (Sold) 0-60 in . . . Never reached 60

Yea if the fluctuating gauge is a constant thing than its those two o-ring in the filter housing. Its good to haves spares of those for every third oil change.
The fluctuation the drosselstift is supposed to correct occurs when the engine has been running for extended amounts of time. Essentially the oil gets so evenly heated up that it flows too fast in the gauge line and whenever you go to accelerate, the increase in oil pressure hits the gauge so fast and erratic that it causes the gauge needle to buzz when it reaches the stop point at the three on the gauge. Its very loud and obnoxious (stop and go traffic was a hellhole +1) and i'm sure it could be remedied temporarily or constantly by oil stabilizer, but I prefer the factory solution.

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A junkyard is not for junk

You'll be okay, have fun and drive safe. I have installed the same item years ago and have never had any issues on long drives. Granted it's probably not the same long drives you are taking, but it's been a few years now and there have been no issues.

If I were you, the only thing that'd bug me is that I tightened the oil gauge line fitting correctly!

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Did you install the drosselstift in the same place? I tightened the oil lines till they were snugged. Should I have used plumbers tape or anything? Btw beige, your auto is quite a looker!

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A junkyard is not for junk

Yes, I dropped it in the oil pressure gauge line. I don't think Teflon tape would have been needed.

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http://farm8.staticflickr.com/7271/7...144c3fc1dc.jpg

Hello, hello, great success! Nearly 2,985 miles and not even a stray fluctuation! The gauge stayed gentle and consistent, read appropriate around 2 at idle, and gently *and silently* hits 3 upon acceleration. No irritating buzzing, nada! I basically shoved the point of the drosselstift into the gauge line as far as it would go, where it connects to the gauge. I used gentle pressure when pushing it in to make sure not to change the shape of the drosselstift.
It's likely that the oil pressure would have just shoved the pin out of the line and into the gauge passage ( probably where it supposed to be), but either way it is all good, and that buzzing never came back, even in the final 500 mile sprint in the blazing hot high desert of eastern California. 9/10 easy install, just confusing without instructions but really not crazy in concept. 10/10 would recommend for long roaders.

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A junkyard is not for junk

On a long hot run or even a reasonable one. Take a temperature reader to make certain the oil cooler thermostat is functional as well. You read the oil cooler temperature. Also the oil cooler hoses should be examined carefully or replaced if thought the original ones.

They blow out generally on the highways and most times you will be left with sticking a fork in the engine. As all the oil is pumped out so quickly. Almost impossible to catch this while driving.

Not that this is a problem just good to make sure the oil cooler is both working as it should be and the hoses are in good shape. I would estimate that with both members and observers on this site combined. Have lost perhaps fifty engines alone from oil cooler hose failures on these engines.