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Discussion Starter #1
I recently moved down to texas and was told by a local dealership that my oil changes should use a conventional oil instead of the synthetic I had always used. This is because of the high mileage on my '92 600 SEL, (153,000). The service "consultant" mentioned that older mercedes with somewhat high mileage should use the conventional to prevent oil seeping from the seals. Therefore they used a mobil 15W40 conventional.

If any experts out there would care to comment on this I would appreciate it. I'm tempted to return to the dealership and get another oil change this time using the synthetic.

Regards,
Rob Frey
'92 600 SEL
'97 Land Rover Discovery
 

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I have a 1994 s420 with 133k miles and synthetic has been used in this vehicle since 90k miles or so. So at one point or the other it was switched from conventional to synthetic. I curretnly dont have noticable leaks and overall I feel better using synthetic in my engine. If I had your engine I would switch, just to feel the comfort of my engine getting max protection with minimal viscocity break down and alot less deposit built up. I found an article online that may help you make your decision. It covers the pros and cons of both.

http://www.ezinearticles.com/?Your-Engine%2C-Your-Baby%3A-Synthetic-or-Conventional-Oil&id=28533
 

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The "best oil" argument has been raging since Penssyvania claimed its parrafin rich oil was better than the oil pumped from Texas wells.

Synthetic oil base is simply a manufactured oil that has a fixed molecular composition - in short it is fairly homegeneous and can be duplicated from run to run. Non-synthetic is produced by cracking and selecting products from the distillate stream. It has varied molecular composition and can vary from run to run. Specifications for this base stock are based on performance during certain tests rather than a fixed molecular composition.

So??? Synthetic oil has well behaved chemical properties that can be tailored to meet the needs of the customer. It does not vary in composition so the lighter distillates do not boil off and form deposits and additives can be selected based on composition, rather than tests on the base stock, as with dino oils.

Synthetic oils usually have a better additive package since there are no variables in the compostion of the base and allowance does not have to be made for run to run variations, do not form deposits since there are no leftover lighter distillates, and have a much better viscosity range without the addition of viscosity improvers which break down and form deposits.

Synthetics will not dry out seals and cause seepage, but a heavy dino oil might not seep past a leaking seal as fast as a lighter synthetic would - hence the urban myth about synthetics causing seal failure. The failure was there all along, just that the dino oil does not leak as fast. Same logic as using 50 weight oil and lots of STP to "cure" ring and seal failure.

Use synthetic if you have been using it all along. Do not go with an extended change unless you are on an oil/additive analysis program like the fleet owners use. Synthetic will make your engine last a lot longer, improve mileage, and lighten your wallet. If it starts to smoke and the seals leak, either get it fixed or cover it up with a heavy dino oil.
 

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Discussion Starter #4
Thanks for all the information. After discussing the subject further with the dealership, it seems that any cars older then a '98 model will expect the conventional oil UNLESS OTHERWISE REQUESTED. So the $80 oil changes I've always paid for, were using a conventional oil. I'll pay the extra $30 for the synthetic from now on.

Rob Frey
'92 MB 600SEL
153,000 miles
 

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That article i posted says 25-50k miles i think that sounds a bit too extreme but maybe true. I change mine every 6-8k miles or seasonly. I use Mobil 1
0w-40, for those with the v12 what are you guys using and how often are you chaning your oil? Thanks
 
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