My 91 300SE has 116K miles on it. I'm female, I don't know a whole lot about cars, but I can change my oil and air filter, fuses, minor type things. I want to be a little independent when it comes to my cars. For my oil changes, I went to Kragen about 3 years ago, and they have me using Max Life 5W 30 Synthetic Blend, which I have not had any issues with. I found an old oil container in my trunk and it seems like I previously used 20W 50, which I believe it what the manual says to use. I could not find a section on this forum for oil info. Do any of you DIY guys have any preferences on what you use for oil? In my 93 Miata I'm using Max Life 10W 30 Synthetic Blend. That car has about 170K miles on it. No issues with that car either. Any advice would be appreciated!!

I dont think you need synthetic oil, I would use Rotella 15w 40 its a diesel oil but is good for the m103. Regular dino oil is good enough, synthetic is a waist of money if you do regular oil changes.

exactly this. Stay away from synthetic in your car, it will cause more problems than it will solve.

Rotella 15/40 only, and if it's cold where you are at 10/40 or even 10/30 in winter.

rjp

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03 540I (GAK!!)
81 280E (W123)
70 LeMans Sport with pissed off Poncho 462"
1989 Silverado Step Side (under the knife- complete restomod)

I'm sorry but that is just bad advice. There is absolutely nothing wrong with running synthetic oil. With that being said, Rotella or Chevron Delo 15W-40 are both excellent oils for their higher ZDDP content. Changing your oil on time and using a quality oil filter are more important than choosing one brand or grade of oil over another.

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1989 300CE

1)- being a 1991 the car wasn't designed with synthetic in mind. Oil has changed and not for the better:

See report by Charles Navarro of LN Engineering: Oils: What motor oil should I use? Which oil is best for my Porsche or aircooled engine?

2)- Synthetic oil has low ZDDP.

3)- it is proven to cause leaks, or hasten the onset of leaks.

4)- why screw with something that works fine?

5- it's a big waste of money, doubles the cost of the oil change and high risk for what? No benefit in this case (unless you count leakage)- a 116K motor that's 20 years old that at best, has questionable seals? That's all you will get.

Don't believe the synthetic hype. You, or the car will not notice the difference. It's marketing BS.

rjp

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03 540I (GAK!!)
81 280E (W123)
70 LeMans Sport with pissed off Poncho 462"
1989 Silverado Step Side (under the knife- complete restomod)

1991 300SE Owne, as you can see everyone has an opinion on the oil and oil viscosity that is best for your engine. If you do a "Search" using "Oil" or "Oil Changes" you will find many threads discussing the subject ... hours worth of reading.

The factory fill for that vintage engine was 15W40 mineral oil. Check the index in the back of your Owner's Manual under "Fuels, Coolants, Lubricants, etc." for the page with a chart that- shows oil grades (weights) versus ambient temperature.

Synthetic oils have swell agents that prevent gaskets/seals from leaking. Since you have been running synthetic oil in your 1991 300SE without any problems it's fine to continue using synthetic oil in my opinion. I use Mobil 1 15W50 in our engines of that vintage and have never had any leakage issues, even when switching to synthetic oil after 100,000 miles. The Service Booklet recommends oil changes every 7,500 miles and I follow that frequency religiously. (I also use Mobil 1 15W50 in my John Deere tractor engine. During a recent camshaft replacement at 1,065 hours, a known Kawasaki engine issue, the service manager said the original cross hatching on the cylinder walls was visible. Meaning the engine showed no/little wear.)

Bottom line: I would continue with synthetic oil. George Murphy, the Technical Director of the Mercedes Benz Club of America, endorsed Mobil 1 during a tech session I attended in 1998 so I have been using it since then. Our local MB dealers use Mobil 1 for all oil changes.

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Fred Hoelzle

Theres a few Mercedes engineers out there that would beg to differed. I switched my m103 to synthetic rotella 5w40 at 150k miles when I bought it. No problems 3 years 37k miles later. I change it once a year regardless of the mileage. If synthetic oil is going to kill my engine it better do it soon before I get bored with it.

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CENSORED due to not family friendly words

But she's not using synthetic oil, but a synthetic blend, which likely doesn't have that much synthetic oil in it. Even Mercedes has acknowledged synthetic oil's propensity to leak. They had to - it's more prone to leak.

"Mercedes engineers" don't recommend anything - they have a long list of approved oils which includes conventional oil for a car of this era. Mercedes North America recommends Mobil 1 but they have a joint marketing agreement with Mobil, which means they are paid to say that - and that sort of an "opinion" should be thrown out as lacking objectivity - tainted by financial interests and contractual obligations.

To the OP, your car isn't sensitive to oil type - synthetic, conventional, blend - are all fine. There are many examples of 300k to 500k mile engines with conventional oil. But you should strive to get the viscosity right for your climate, as your 1991 approved fluids booklet specified. You haven't told us where you live. 20-50 would be suitable for the desert summer but not for a New England winter.

I use 15w40w diesel oil spring,summer,an fall.Winter I run sync 5w40 diesel oil

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Another typical oil thread argument.
Biggest waste of time is agonizing over it. Just buy a good name brand oil which is of the viscosity appropriate for the season the oil will be used in. If you don't change it very often (because it isn't used much) I'd recommend 10w40 as a good all-around oil, unless you live in extreme temp areas (far north or south).
A couple favorite brands would be Penzoil or Castrol.
If you want to run synthetic you can do that, there are some pluses to running it, but I would insist that you can run the engine for more miles if you use it, probably twice as long. It costs twice as much, so might as well get something "tangibile" for what you are spending.
For change-out mileage specifics, what I recommend and has always worked well for my vehicles, is change the oil based on 1000 miles for every quart of capacity, so if your 300se takes I believe 6.5 quarts, go 6500, or if you run synthetic I'd go twice that, 13000.
Gilly

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Gilley I stll change filters and top off oil if running sync oil every 3500 miles.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Deanyel, I am in Northern CA, Sacramento area. I can't find my manual at the moment, and after I found the old bottles of 20W 50 in my trunk, I decided to do the post. I used the 20W 50 when I lived in Los Angeles. I'm not sure now that Kragen's advice of 5W 30 is the best? I do change my oil every 7,500 miles, probably earlier than that. I used to change it every 3,000 like I do with my Miata.

It's my understanding that by using the synthetic 'blend' I could go back to regular oil if I wanted to. That is why I was using the 'blend'.

Gilly, I'm not driving my Mercedes much at all, mostly due to the price of premium gas vs mileage the car gets. There have been years when I've only put about 2,500 miles on it. My little Miata gets great gas mileage, I mostly drive that car. I guess I have been agonizing over the oil. My main concern is that I don't put in oil that will mess up my engine. I want my Mercedes to last me for my life, I don't want to have any more car payments.

Ok, what are the benefits in this case?

Bottom line is this- the M103 is a flat tappet engine, you want to risk potential camshaft damage using the latest low ZDDP AND risk leakage AND spend 2x the amount you normally spend?

Makes no sense gents.

Dino oil in these engines is fine, don't fix what isn't broken.

rjp

__________________
03 540I (GAK!!)
81 280E (W123)
70 LeMans Sport with pissed off Poncho 462"
1989 Silverado Step Side (under the knife- complete restomod)

PS- my engine has said 15/40 rotella, per the owner's manual, zero usage at 165K in Phoenix, AZ year round.

5k intervals.

works fine.

rjp

__________________
03 540I (GAK!!)
81 280E (W123)
70 LeMans Sport with pissed off Poncho 462"
1989 Silverado Step Side (under the knife- complete restomod)