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TimBru99 05-05-2000 09:26 AM

Benzmac and others,

I know this is a subject that has been covered before.

I have recently acquired a C-class, 1994 with 58,000 miles. I want to use synthetic lubricants such as engine oil, transmission fluid, and differential grease. Is it too late to start???

I see no perceptible oil leaks but I have heard the reports that synthetics, especially engine oil, will make leaks appear when there weren't any before.

I have never used synthetics before so I have no experience base.

Recommended brands? Most of the major brand names have synthetics now. I know of Mobil-1, Amzoil, Redline, etc?

Experience and opinions are appreciated.

Roger 05-05-2000 11:28 AM

I have a follow up question. If someone trys synthetic and gets leaks, Will the leaks eventually go away if you switch back to natural oil?

jeffsr 05-07-2000 11:12 PM

If you had leaks before, you will still have them. Synthetic oil does not produce leaks per se, but due to it's increased flow characteristics, it will make pre-existing leaks seem worse. Changing back and forth will not make leaks go away.

Jeff L
1987 300e
1989 300e
1987 BMW 325

Roger 05-08-2000 12:52 AM


Thanks for the reply.

I seems to me then that if I have absolutely no leaks now evidenced by an engine that remains reasonably "clean" (no significant oily buildup on the engine over time), and I change to Synthetic oil, then I probably still get no drips. That is what I thought, but from the posts here, it seemed that synthetic MADE engines leak.

I take it then that engines with oily build up may have leaks that evaporate before dripping, but if synthetics are introduced the leak rate may grow to exceed the evaporation rate, hence drips.

If this is true, might it be predictable when synthetic oil is likely to be a problem?

Just wondering if I have made an incredible intuitive leap, or gone one beer too far.


jeffsr 05-08-2000 07:06 AM

Roger, Don't get caught up in all of the silly debate about synthetic vs dino oil. Put it in this perspective. When the oil companies were done with the R&D on synthetics. (BTW, they have been around for quite a while. Used for many years in jet engines and other high temp applications). If there was the least concern that synthetic oil would eat seals, etc, then if they released it for automotive use, they would have been setting themselves up for legal problems. Synthetic oil has a better set of additives and is more viscous than "natural" oil. Can go longer between changes. That by the way is an issue that will always be debated, ie. how often do you change the syn oil. Go ahead and change over, if you feel strongly about using syn. You will do no harm to your car. If changing were a problem, then all new cars would have to be redesigned for syn and we would have warnings about the danger of changing. I think there are a couple of high performance production cars out there that come from the factory with syn. I use Mobil 1 in my 87 300E with no problems other than having to keep my wallet out longer when I change the oil :D... Don't worry, be happy. Syn oil is not a new development. It's been around for a while, and I don't think it will eat your car.

Jeff L
1987 300e
1989 300e
1987 BMW 325

ctaylor738 05-08-2000 10:00 AM

My advice from personal experience is not to use synthetics in the transmission. I had a Porsche 928 (which uses a Mercedes automatic) that did not leak until an overachieving mechanic recommended Mobil One. Thereafter it leaked out the rear seal and changing back to regular did not help. The mess on the garage floor was bad enough, but it got onto the exhaust pipes which caused a nauseating stench.

My advice is that if the car does not leak, do not do anything that might cause it to start.

Frank King, the late Tech Director for the Mercedes Club was adamant about not using synthetics.

Chuck Taylor
Falls Church VA

Michael 05-08-2000 10:34 AM

$.02 time...

I switched my '88 300TE to synthetic when it was 8 years old, and it definitively started to leak more. However, I'm a huge advocate of synthetics (my Honda with nearly 300k on the clock's never been apart, but when I replaced a rusting oil pan at around 260k I saw what appeared to be a brand-new engine on the inside) so I replaced the leaking seals (front crank seal, rear crank seal, front cover seal) and am convinced I won't have to again for a LONG time. However, when I tried out Red Line synthetic motor oil (which per the manufacturer is more of a "purist" synthetic than Mobil 1 and thereby lacks the additives that make your seals swell like dyno oil does) my reward was new leaks. Switched back to Mobil One; leaks gone. You decide what this means.

Now, as to the tranny issue broached by Chuck T., I was not aware that Mobil has ever produced a synthetic transmission fluid of a variety suited to a 928/MBZ auto tranny. Could that have been the problem? Please advise as to what specific product you used. I run Redline Synthetic ATF in both of my cars and it's been fabulous, and a marked improvement over conventional ATF in the cold (smooth shifts at very low ambient temps)and neither tranny leaks. My bro-in-law's run the same stuff in his '88 300TE from 100k miles to the present (just shy of 300k) and even though that tranny slipped when he got it, it never worsened and he got another 200k out of it! It's finally starting to really die, so he's popping an MBZ unit in this week, and will unquestionably run red Line Syn in it; he's now a convert and only runs synthetics.

I hope this helps.

Best regards, Michael
'92 500E
'88 300TE

Roger 05-08-2000 10:37 AM

Thanks for the comebacks. I personally have no interest in switching to synthetics. Just wondered about the chemistry / physics of the leaks.

Proud consumer of refined Texas crude with selected OPEC fillers.

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