Yet Another Motor Oil Thread - Mercedes-Benz Forum
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post #1 of 22 (permalink) Old 06-20-2019, 04:12 PM Thread Starter
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Yet Another Motor Oil Thread

My ’94 E420 had run its entire life on Mobil 1 15W-50, without issue. (I am in TX, so the ambient temperature can be quite high, hence the high viscosity.) Then I discovered that Mobil had quietly switched from Group IV and V base stock to Group III base stock, which I viewed as both hypocritical and underhanded. Hypocritical, because Mobil sued Castrol for calling their Group III base stock oils “synthetic” while Mobil did the exact same thing after the ruling was in Castrol’s favor; and underhanded, because they did so quietly, without informing their customer base.

I switched to Royal Purple HPS 20W-50. My second oil change with Royal Purple was at a 7,200 mile interval, which is significantly longer than my standard 6,000-mile oil change interval. ~ 3 weeks prior to this last oil change, I noticed that my oil pressure gauge was acting wonky (rapid fluctuations, sometimes pegged at max – even at idle, or 1bar when cruising at 80 mph, when it should have been at 3 bars). Today, I took my vehicle into my Mercedes mechanic for him to check out since I thought it might be an oil pressure sending unit issue. I also had him change the oil and filter with Royal Purple HPS 20W-50. The mechanic said that after the oil change the oil pressure gauge was reading/operating properly, which I confirmed, albeit only briefly. Irrespective of the oil pressure gauge/sending unit, my mechanic stated that there is not an actual oil pressure issue.

My concern is two-fold 1) my mechanic said that the oil filter was showing the very first signs of sludge build-up (filminess), which I thought was unusual for a top-tier motor oil such as Royal Purple – even at 7,200 a mile oil change interval, and 2) the oil seems to have interfered with my oil pressure sending unit. Since my vehicle has 240,000+ miles on it, he suggested that I switch to Valvoline 20W50 Extended mileage conventional (Mineral) oil. I found that Valvoline does make a synthetic blend Max Life in 20W50, but they do not seem to have a full synthetic “high mileage” oil in either 15W50 or 20W50. While I understand that synthetic motor oil is not required for my 119 engine, I don’t really want to switch back to a conventional motor oil since the vehicle has run synthetic oil for its entire life.

Now I’m confused about what motor oil I should use. While I haven’t lost faith in Royal Purple just yet, I am concerned about the possible sludge issue – even if it was just beginning to present. The oil pressure interference is another issue that may or may not be attributable to Royal Purple.

I would like to use a synthetic oil that is relatively easy to source and is a genuine synthetic oil (group IV or V base stock). Lubro Moley and Motul are difficult to find, but can be ordered online. Red Line is expensive. I’m not sure what other 15w50and 20W50 oils I should consider and I’m not sure if a High Mileage formulation is beneficial or necessary.

Any recommendations based upon experience would be appreciated. Thank you.
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post #2 of 22 (permalink) Old 06-20-2019, 04:57 PM
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Royal Purple HPS is good stuff, though it is pricey. Doubt that it is the source of any sludging, especially after only 7200 miles, though the additive package might just be removing some from a 240kmi engine. Were it me, I'd stick with it if it is affordable to you, but maybe shorten the change intervals for a few changes.

Not to plug another forum (OK, I am), but there's one called "Bob Is The Oil Guy," and those guys over there talk about oils as much as we talk about cars and can likely give perspective on your oil selections and the performance in various engines with used oil analyses to back it up.


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post #3 of 22 (permalink) Old 06-20-2019, 05:06 PM
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Originally Posted by 1994 E420 View Post
My ’94 E420 had run its entire life on Mobil 1 15W-50, without issue. (I am in TX, so the ambient temperature can be quite high, hence the high viscosity.) Then I discovered that Mobil had quietly switched from Group IV and V base stock to Group III base stock, which I viewed as both hypocritical and underhanded. Hypocritical, because Mobil sued Castrol for calling their Group III base stock oils “synthetic” while Mobil did the exact same thing after the ruling was in Castrol’s favor; and underhanded, because they did so quietly, without informing their customer base.

I switched to Royal Purple HPS 20W-50. My second oil change with Royal Purple was at a 7,200 mile interval, which is significantly longer than my standard 6,000-mile oil change interval. ~ 3 weeks prior to this last oil change, I noticed that my oil pressure gauge was acting wonky (rapid fluctuations, sometimes pegged at max – even at idle, or 1bar when cruising at 80 mph, when it should have been at 3 bars). Today, I took my vehicle into my Mercedes mechanic for him to check out since I thought it might be an oil pressure sending unit issue. I also had him change the oil and filter with Royal Purple HPS 20W-50. The mechanic said that after the oil change the oil pressure gauge was reading/operating properly, which I confirmed, albeit only briefly. Irrespective of the oil pressure gauge/sending unit, my mechanic stated that there is not an actual oil pressure issue.

My concern is two-fold 1) my mechanic said that the oil filter was showing the very first signs of sludge build-up (filminess), which I thought was unusual for a top-tier motor oil such as Royal Purple – even at 7,200 a mile oil change interval, and 2) the oil seems to have interfered with my oil pressure sending unit. Since my vehicle has 240,000+ miles on it, he suggested that I switch to Valvoline 20W50 Extended mileage conventional (Mineral) oil. I found that Valvoline does make a synthetic blend Max Life in 20W50, but they do not seem to have a full synthetic “high mileage” oil in either 15W50 or 20W50. While I understand that synthetic motor oil is not required for my 119 engine, I don’t really want to switch back to a conventional motor oil since the vehicle has run synthetic oil for its entire life.

Now I’m confused about what motor oil I should use. While I haven’t lost faith in Royal Purple just yet, I am concerned about the possible sludge issue – even if it was just beginning to present. The oil pressure interference is another issue that may or may not be attributable to Royal Purple.

I would like to use a synthetic oil that is relatively easy to source and is a genuine synthetic oil (group IV or V base stock). Lubro Moley and Motul are difficult to find, but can be ordered online. Red Line is expensive. I’m not sure what other 15w50and 20W50 oils I should consider and I’m not sure if a High Mileage formulation is beneficial or necessary.

Any recommendations based upon experience would be appreciated. Thank you.
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post #4 of 22 (permalink) Old 06-20-2019, 05:10 PM Thread Starter
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edfreeman: Thanks for the reply, although I question whether or not the Royal Purple removed any sludge from my 240K engine because: 1) Prior to my switch to Royal Purple I used Mobil 1 15W50, which kept the engine clean and 2) this was my second oil change using Royal Purple and the first time I used it I ran it for a bit over 6,000 miles and there was no sign at all of filminess or sludge.

I purchase Royal Purple HPS 20W-50 in the 5 gallon jug for ~ $150.00, so my per qt. cost is ~ $7.50, which is reasonable.

I will check out the oil forum you recommended.

Last edited by 1994 E420; 06-20-2019 at 05:25 PM.
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post #5 of 22 (permalink) Old 06-20-2019, 08:09 PM
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Many of the US branded 'fully synthetic' oils would not be permitted to be sold as such in Western Europe, as the criteria to qualify are stricter.

40 miles or so before an oil change, old time mechanics used to add a 3/4 to a quart of ATF to the engine oil and drive before draining.
The detergents in the ATF would help get rid of sludge.
I have done it on both M117 and M103 engines, but better talk to your mechanic first.
Modern engines machined to much smaller tolerances probably won't require anything like it.
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post #6 of 22 (permalink) Old 06-20-2019, 08:15 PM Thread Starter
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I was just advised that Mobil 1 is now using Group IV in the form of Alkalated Naphthalene, and that some blends are using POEs (synthetic esters). Mobil 1 is also using more GTLs (gas to liquid) in place of any group 3 base stocks.

So maybe I'll simply switch back to Mobil 1 15W50 at my next oil change, which would certainly be the course of least resistance.
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post #7 of 22 (permalink) Old 06-20-2019, 08:19 PM Thread Starter
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Many of the US branded 'fully synthetic' oils would not be permitted to be sold as such in Western Europe, as the criteria to qualify are stricter.
Yes, I am fully aware of the ramifications of the Mobil/Castrol lawsuit, one of which is that American companies can get away with much more liberal interpretations of what is considered a "synthetic" oil.

Thanks for the ATF recommendation, but I don't think I'll be going that route. I've had the valve covers off in the last year and there wasn't even a hint of sludge. The Mobil 1 I had been running for the last 24 years did it's job well.
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post #8 of 22 (permalink) Old 06-20-2019, 09:12 PM
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An acquaintance distributes ELF-Total, so I have been using their synt for years. When I got the W201 2.6 with 50.400 miles, the shifts were a bit harsh for my taste. I have been running CARQUEST DEXRON®-VI FULL SYNTHETIC ATF in the transmission for over 60 k miles, with one filter and fluid change when I got the car, and another in between, and it has served me well.
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post #9 of 22 (permalink) Old 06-20-2019, 09:26 PM Thread Starter
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Teutone: Thanks, I will look into Elf-Total.
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post #10 of 22 (permalink) Old 06-21-2019, 01:22 PM Thread Starter
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I was advised to only use a motor oil approved by MB. Mercedes-Benz approval 229.3 is correct for my ’94 E420. The only 50 weight oil listed is Mobil 1 5W-50. There are numerous other oils listed in 0W-30, 0W-40, 10W-40, 5W-30 & 5W-40. Considering that I have used M1 15W-50 for the last 24 years and RP 20W-50 only for my last 2 oil changes, and that my engine has 240K, would there be any issue switching to a lighter viscosity? Also, I wonder why so many Mercedes mechanics recommended M1 15W-50 for my vehicle if it’s not listed on Mercedes-Benz approval 229.3? Although M1 15W-50 is not listed on MB Approval 229.3, it is listed on other Approval forms for other older MB V8 engines. I’m inclined to switch back to M1 15W-50 since I have used it for so long without any issues whatsoever. Or, perhaps, M1 5W-50. What say you?
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