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Old 08-13-2001, 09:04 PM
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Can I use 20W50 oil year round?

I've looked through the oil discussions and didn't see the answer. If I missed it, please excuses the repetitive question.

I just bough my E320 1994 w/108,000 miles a few months ago. I'm using 20W50 weight Castrol and want to keep using it throughout the winter if it won't do any harm in the average 20 degree lows of our South Carolina winters.

I'd appreciate any opinions from this informative group.

Thanks in advance.

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Old 08-13-2001, 10:25 PM
longston's Avatar
Another View. . .
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Location: Mark West, CA
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Same Answer, New Day...

Read your owner's manual, and see what Mercedes recommends for oil viscosity based upon your climate where you live...
"We drive into the future using only our rearview mirror."
- Marshall McLuhan -

Scott Longston
Northern California Wine Country...
"Turbos whistle, grapes wine..."
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Old 08-14-2001, 05:03 AM
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I looked in the Mercedes oil guide and it says that 20w50 is good to +23 degrees Farenheit. The next rating, 15w is good to +5 degrees farenheit.
I would recommend atleast 15w just to be safe. Mobil 1 synthetic has 15w 50, which is what I use, and would seem to work well for you also.
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Old 08-14-2001, 08:42 AM
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In your climate I don't think 23 degree minimum temp of 20W50 versus the expected 20 degree temperature is a big problem.

The problem with 20W50 is the fact that there is an inordinate volume of an additive called "Viscosity Index Improver" added to the oil to make a 30 weight spread from 20 to 50. This amount of VI additive is known for causing excessive "coking" or carbon buildup, particularly in smaller, hard working engines such as yours.

If you like Castrol products, and they are good products, you should consider using something with a little less spread. Even limiting the spread to 25, such as with 5W30 or 15W40 will make a dramatic difference in the amount of VI contained in the oil. To make that extra 5 weight spread takes much more VI additive, it is not a linear relationship.

Check out what is available, and also refer to the oil weight chart in your owners manual as recommended by previous respondents.

Best of luck,
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Old 08-14-2001, 11:11 AM
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Originally posted by LarryBible

The problem with 20W50 is the fact that there is an inordinate volume of an additive called "Viscosity Index Improver" added to the oil to make a 30 weight spread from 20 to 50. This amount of VI additive is known for causing excessive "coking" or carbon buildup, particularly in smaller, hard working engines such as yours.
If I may...the problem with the V-1 modifyer was limited to 10W40 oil. GM study done in the early eighties...Volvo voiding warranties if it was used...etc..
Since 20w50 starts with a base that is twice as thick as 10w40, the problem doesn't show up. I doubt there is a name brand oil maker on the planet that still makes the "evil brew" that caused the problems.
Back to the question at hand, I don't think you would have a problem using 20w50 oil, but consider the switch to Mobil-1 15w50 and run regular oil changes instead of short-cycle 3K mile changes. I use 15W50 all year in everything I have, and it gets really cold up here Really cold . But then, when it's 20 below zero, nobody "has" to go anywhere do they.
Randy D.
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Old 08-14-2001, 12:16 PM
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I learn somethin' new every day.

Thanks for the update.

Have a great day,
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Old 08-14-2001, 04:55 PM
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Join Date: Jan 2000
Location: buckhorn, ontario, Canada
Posts: 101
follow-up for Randy

Since Castrol (GTX) comes in a popular 10W40 grade which I planned to use in my next change, I would like to clarify my understanding of one of Randy's comments on this subject. Am I correct in understanding that the current 10W40 formulation (of Castrol and others) should be perfectly fine, and that in spite of earlier problems with 10W40 the V-1 modifier is no longer an issue.
Thanks for your expert input on this topic.

'86 300E
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Old 08-14-2001, 04:59 PM
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Join Date: May 2000
Location: Soperton, Ga. USA
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Looks like another oil forum starting . I have been running Castrol 20W50 for I don't know how many years without any problems. The last engine that I tore apart (after the wife ran it air cooled until it stopped) you could eat off any of the internal parts of the engine it was so clean.
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Old 08-14-2001, 06:26 PM
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Thanks so much for the very informative replies to my question. I was considering going to 10W40 Castrol for the winter months, but I was a little concerned that it might be a little too light weight for this engine on those winter days when the temperature gets back up into the 60's here in South Carolina.

Before sending this post, I did go through the owners manual from cover to cover looking for ANY information on suggested oil weights. The manual looks complete, but there must be some information that wasn't with the car manuals when I bought it. I've been changing my own oil in all of my cars for the past 35 years. (That's about the extent of my mechanical ability, but it does make me feel like I'm able to do the most important PM service for the car).

I don't know why, but I'm still a little reluctant to go with a Synthetic oil in an older car that wasn't weaned on it. I'm probably wrong in being concerned.

Thanks again all,

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