Here are the results of the oil analysis. Unfortunately, I cannot attach images, so I will have to summarise.
Mercedes 240D 1979
OM616 2.4L, 4-stroke, diesel
Shell Rotella T SAE 15W40, 5.7 litres
Oil filter: BOSCH 72126WS premium filter
Last oil change date: 17 Feb. 2018
Last oil change mileage: 176,342 miles
Motor burns oil, thus:
Added oil date: 30 Sept. 2020
Added oil mileage: 177,899 miles
Added oil quantity: 2 litres
Mileage at oil analysis test: 178,202 miles
Date of sample: 2 Mar. 2021
Mileage on vehicle since last full oil change: 1860 miles and 2 years
Mileage on the 2 litres of oil added between changes: 303 miles and 5 months
Usage: Like the Jeep, the Benz only sees short trips of about 2-6 miles in slow moving, frequently stop, city traffic.
Results: All wear metals, contaminant metals, multi-source metals, additive metals, fluid properties, other contaminants, and particles within normal range.
TECHNICIAN NOTES: Data indicates no abnormal findings. Resample at normal interval.
Sorry, it will take too long to type out all the actual values, but nothing was flagged. On the severity scale of 0 to 4, the results was a 0.
Jeep Cherokee Sport 1999 4WD
Inline-6 4.0L, unleaded gasoline
Valvoline Fully Synthetic SAE 10W30, 5.7 litres
Oil filter: FRAM Tough Guard TG16
Last oil change date: 23 Feb. 2020
Last oil change mileage: 107,421 miles
Mileage at oil analysis test: 109,617 miles
Date of sample: 2 Mar. 2021
Mileage on vehicle since last oil change: 2196 miles and 1 year
Note 1: Changed valve cover gasket 1 week before oil sample taken
Note 2: 14 Oct. 2020 @ 108,175 miles, added 8 oz of Blue Devil Rear Main Seal Leak Stop (contains diethylene glycol monoethyl ether according to the first aid info on the bottle)
Note 3: I may have used Lucas Engine Oil Leak Stop a week before the Blue Devil, but I did not record it on my service log. My memory is that I did, and waited a week to see if it was going to stop the leak, it didn't, so I added the Blue Devil (which worked well until recently).
Usage: 8:30 AM, 3 mile trip, car off 2 min, another 3 mile trip, car off, at 2:30 PM another 3 mile trip, Car off 2 min, then another 3 mile trip. That is its core function, plus maybe a Saturday trip to the grocery store.
Results: Silicon levels slightly elevated at 28 ppm. Also slightly out of range were the Sodium at 109 ppm, Molybdenum at 38 ppm, Boron at 76 ppm, Magnesium at 415 ppm, and Calcium at 1110 ppm [perhaps caused by the oil leak stop additives?]. Base No. D4739 was low at 3.13 mg KOH/g.
The overall severity based on the results were a 1 out of 4, with 0-1 being "Normal", 2-3 being "ABNORMAL", and 4 being "CRITICAL".
TECHNICIAN NOTES:
Silicon is at a MINOR LEVEL; SILICON sources can be abrasives (dirt, Alumina Silica), seals and gasket material, lube additive or lube supplement, and/or environmental contaminant; Base Number is SLIGHTLY LOW. As Base Number depletes, the ability to neutralize acids is diminished. Flagged additive levels are different than what should be present for the identified lubricant. This may have been topped off with a different lubricant, the fluid may be misidentified, or a different lubricant or formulation may have been in use prior to a recent change.
Comments from the lab were that it looks like additives were added to the oil but not noted by the customer. lol, yup! Forgot about the Blue Devil Leak Stop being added in there some time back. Nonetheless, the oil in its present form still appears in the normal condition.
In conversation with the oil test guy, he didn't think the Benz needed an oil change, but cautioned that the oil filter elements break down over time and I may want to change it in the future if I don't change the oil.
For the Jeep, he felt the result was expected for having changed the valve cover gasket and added oil stop products. Changing the valve cover gasket will leach Silicon into the oil and this is the likely reason why the Silicon level was slightly elevated. He did mention that I may want to consider using the thicker 15W40 oil in the Jeep to help with the oil leak. He also commented that there is a large range in what it takes to be called "synthetic" oil, noting that even highly refined mineral oil can be called synthetic. He said that pound-for-pound, the heavy duty diesel is normally a better formula out of the bottle. He commented that diesel oils tend to be more robust than passenger car oils in terms of detergents and anti-wear additives. Diesel oils likely start out with a higher base number and are often formulated to maintain that base number longer than gasoline oils.
I was going to change the oil pan gasket this weekend, which will require an oil change, and wasn't sure if I was going to use the 10W30 synthetic or 15W40 diesel oil. I was a bit concerned that the 15W40 might not last the 2 years I'm hoping to push oil changes, but from the Benz results, it doesn't seem bad at all From the results, it seems like the 10W30 fully synthetic might be OK for an oil change every 2 years with my driving. The Benz was OK at 2.5 years with Rotella 15W40, but of course the car burns oil and I have add about 1 litres per year. The Jeep doesn't burn oil.
The end goal I am hoping for is an oil change every 2 years on both vehicles.
The Benz seems OK for this. For the Jeep, I have exactly 6 quarts of unused fully synthetic, so will use this for when I change the oil pan gasket. If the leak continues, I'll add the Blue Devil again. If leak continues, I'll change the oil after 1 year and switch to diesel oil. The leak isn't all that bad right now, perhaps 2 dime-sized drops per week on the garage floor. If after 1 year no leak, I may push for a 2nd then have it tested again. If I switch to 15W40 diesel oil, I'll have it tested after 1 or 2 years and report back.
Maybe some of you can share some of your test results for comparison?