Sometime in the past year there was a post to a thread here from a guy who switched his diesel MB from synthetic to dino oil and said the engine made much more noise on dino oil. No data was included and I've been unable to locate the original thread, which wasn't about oil (as I recall) anyway.

I decided to run my own test by making two videos of my car idling on dino and on synthetic, then compare the two to see if I could detect any difference in engine sounds. (This is by no means a controlled scientific test.)

Vehicle: 1995 MBZ E300 Diesel
Miles on vehicle/engine: ~200,000
Original (not rebuilt) engine: Yes
Oil used for most of the vehicle's life: Unknown, probably dino
Fuel: Commercial B20 (80% D2, 20% biodiesel)

Synthetic oil used for the test
Chevron Delo-400LE Synthetic 5W-40 (group 3) Rated CJ-4, CI-4, CI-4+, etc. plus. MB228.31. The group 3 synthetics supposedly have good wear properties and wide temperature tolerance but don't have the long-life of a true group 4 synthetic or so GSXR says.

Dino oil used for the test
NAPA Premium Performance Universal Fleet Plus 15W40 (made by Ashland Oil). Rated CJ-4, CI-4, CI-4+, etc. No MB rating. It should be similar to other quality dino-based diesel-rated oils.

Test conditions
For each portion of the test (before recording the video) the car was driven on the streets and highways of Sonoma County, California during a normal morning of running errands (20 to 30 miles). The final leg would have been at 55 mph ending at our driveway. The engine was allowed to idle with the hood up and the climate control off. My iPod Touch recorded 30 seconds of video and sound, hand-holding the iPod a couple of feet in front of the car. Ambient outdoor temperatures were in the mid-80s. The synthetic oil had been used for six months and 5,000 miles while the dino oil was fresh. In that one criterion the test was unequal. I'll repeat the test next winter when the dino oil has 5,000 miles on it.

Here are links to the two videos, "Test 1" and Test 2." I won't tell you now which one is synthetic and which is dino. Personally, I can't tell them apart.

Test 1 Video by Jeremy5848 | Photobucket

Test 2 Video by Jeremy5848 | Photobucket

I don't make any claims for these oils -- they were what I happened to have on hand. My current practice (subject to change without notice) is to change oil and filter at 5,000 mile intervals, using dino for the summer and synthetic in the winter for its cold-flow properties. Driving the '95 E300 10,000 miles/year means I change oil twice a year. My wife's '96 E300, driven only about 5,000 miles/year, uses synthetic year-round, changed annually.

YMMV,
Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Hi Jeremy. This is an interesting subject. I've always sensed a quieter engine after an oil change (with the same type of oil, not comparing dino to synthetic).
If you would like to borrow my sound level meter I would be happy to loan it to you for as long as you need, it might allow a more scientific approach to this subject but location of the microphone of any type is critical, a slight movement will significantly affect the captured sound level and quality so any test of this kind needs to be reproduced precisely.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

An interesting suggestion, thanks. I have several such meters, didn't even think about trying them. Mounting the meter on a tripod and using a tape measure to set the position should be sufficient. I'll have to watch the wind speed, though.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

We have to remember that synthetic oil is a lot better cleaner then Dino. Running it through will clear up all the carbon and gunk that has filled voids/cracks in rings seals.....thus you really notice how worn your engine is. I tried synthetic and it was way to thin, burnt off fast and started coming out of everywhere....I went back to Dino....I would love to get a factory new engine and start it right away on synthetic but no one wants to donate me the money

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I went Dino to Rotella T6 about 3 years ago. 5W-40W on the Rotella T6. I have noticed better starting all times of year and no leakage or any oil burned till now.

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1982 300SD

I purchased a junkyard 603 6cyl several years ago out of a 300SDL. the oil was crystal clear. I have never seen this in a diesel and changed it anyway for need to know basis.
The rotella 15/40 turned black within a few days and the oil change interval grew shorter with increased commuting.
Synthetic oil when introduced came black water out of the bottle. I had very little trust in it. I have a V8 gasser that lives on synthetic and I am not going back.
I am switching my Diesel back and moving my wife's t-bird over to synthetic.
If Mercedes and AMG are betting on 300,000 mile gas engines I will be in line.

All the best, Mike