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Old 02-15-2002, 12:10 PM
Posts: n/a
synthetic oil leak

I can verify what a number of messages have said about older engines, changing to synthetic oil, and leaking. With 20-50 dino, I had an occasional drop of oil, maybe about 1 or 2 times a week. I changed to 5-30 about 2 weeks ago, and immediately began dripping a drop or 2 every night. (From either the rear seal, head or valve gasket; no one can seem to say for sure....)

My mechanic said it had been a mistake to change, and that with synthetic I could expect to develop leaks. He said the main problem was that once the oil began to leak through seals, it essentially, as I understood him to say, opened up the seals or holes in the seals, and switching back at that point would do no good. The damage would have already been done.

So, I switched back to 20-50 yesterday, and this morning found drops of oil!

I have a 73 450sl with 112,500 miles.

I think the lower viscosity may have had something to do with it, but my mechanic said that even higher viscosity synthetic was a bad idea. He said synthetics were really formulated for more modern engines, especially turbos.
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Old 02-15-2002, 12:44 PM
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synthetic oil keak

I changed to Mobil 1 10-30 in my '79 450SL at 70,000 miles. I did notice some good size puddles of oil under the car. When I would check the dipstick it read low, so I would add more oil, up to the full mark on the dipstick. Then more puddles of oil, puddles meaning about 6 or 8 inches in diameter. WRONG. I have now learned that my car likes to have between 7 to 71/2 quarts of oil not 8. It seems to purge out the excess oil. Keeping the oil at this level I have no leaks with synthetic.

'79 450SL
76,000 miles
(hibernating till spring)
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Old 02-15-2002, 02:17 PM
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I think you have a point. The guy who put in the synthetic put in over 8 quarts. I actually had some drained out, but it still leaked. When I just changed back, I put in 7.5.
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Old 02-15-2002, 11:59 PM
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I re-read my initial message, and it should have read that after switching back to 20-50 dino, I found NO drops of oil.
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Old 02-16-2002, 11:03 PM
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Join Date: Nov 2000
Location: Vernon, CT
Posts: 1,845
I would agree that some of the leaks were due to the switch, but I think the biggest factor was the drastic change in weights. If you still would like to use synthetic, try 15W-50 Mobil 1.
1994 MB E320 Coupe (199,500 mi)
1992 MB 190E 2.6 (173,000 mi)
1983 Porsche 911SC (148,000 mi)
2004 Volvo V70 2.5T (198,000 mi)
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Old 02-17-2002, 11:10 AM
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Join Date: Dec 2000
Location: Fairfax County, Virginia
Posts: 856
Is 5-30 a good weight for a 28 year old car with 117K?

It would seem an OK winter weight on the car new, but I would expect there would be a lot of seal drying and ring/valve stem seal wear that would drive one to consider a bit more viscous oil ...

Agree that 15-50 would be a good alternative - and, it still retain significant cold weather starting attributes ... ie does not thicken as much at low temps like dino oils do.
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg
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Old 02-17-2002, 12:11 PM
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Join Date: Oct 2001
Location: Canada
Posts: 298

Just want to share my experience with you, I switched to Mobil-1 5W30 when my W124 400E was 10 year old at 200k km, before that it had been using dino. There is some slight oil seeping from camshaft seals, but it has been there even with dino, I have driven 7000 km since I switched to synthetic, didn't notice any oil loss.

Not sure about your 28 year old, it may use different seals and gaskets, the result may be different.
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.
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