Can synthetic motor oil cause leaks?

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  #1  
Old 04-21-17, 06:34 AM
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Can synthetic motor oil cause leaks?

I've read before the notion that synthetic oil is so slippery that it can seep past seals and cause leaks that wouldn't happen with conventional oil. I always thought this idea was BS but I might be experiencing this on my own car now.

I have an Olds Aurora, 2003 with 135,000 miles. Runs great. Several months ago I switched to full synthetic (10W30) and soon after a spot appeared on my driveway. It's gotten worse and now the whole lower engine & cradle are grimy and the dark spot has grown to 2 feet. I now add a quart of oil about every 2000 miles to replace what's dripping and what's now fogging out the tailpipe (noticeable but not objectionable).

Coincidence or "cause & effect"?
 
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Old 04-21-17, 08:16 AM
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Synthetic

With age and mileage it is possible that seals and gaskets have hardened and with all the expansion and contraction of the metal over the years, the leaks may be a coincidence.

But it is true that synthetics have a solvent like effect and can dissolve and clean out an engine with deposits embedded, which can also offer a sealing type of effect. It is the dissolving of the deposits that causes the leaks, rather than the oil or "slipperiness" being the direct cause. On old cars, generally before 1990, the original seals of the engines may not be able to withstand the esters in synthetics (being a type of alcohol), and the synthetic could actually degrade the seals.

Because of the cleaning effect, it would be a good idea to change the oil and filter earlier than you might otherwise. You might change back to regular oil, it is the waxy strands in regular base oils that tend to accumulate with engine deposits around the gasket areas, and the engine might well "reseal" over time with the change back. You might try one of the high mileage regular oils which have seal swelling additives that do work for minor leaks.
 
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Old 04-21-17, 08:20 PM
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That's why I keep saying - enginemust be tested for synthetic feasibility before jumping on it. Start with semi synthetic, see how how goes it. Or blend. If there are no leaks - then go full synth.
Now Pandora's box is open. Go back to regular oil, 10W30, and add Lucas oil treatment. Do NOT go for synth anymore.
 
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Old 04-21-17, 09:50 PM
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likely just a coincidence would get the leak checked out to find out the location and see about having it repaired, really wouldn't expect switching back to conventional oil or high mileage oil or adding other types of additives, will really help to resolve the issue.
 
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Old 04-22-17, 07:15 AM
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First and foremost, there's no such thing is synthetic motor oil causing an engine leak. While this was true decades ago, today's synthetics do nothing to seals, gaskets, or other parts that wouldn't occur with a similar conventional oil.

Beyond that, though, synthetic oil molecules are smaller than those of conventional oil and it certainly possible for synthetic oil to leak from an area too tight for other oils.
 
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Old 04-22-17, 07:19 AM
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Not causing. Simply leaking out. Tolerances in older engines are not designed for synthetics. Also, on a 135 000 miles engine tolerances are higher than they were on new engine.
 
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Old 04-24-17, 06:29 AM
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Are there any know leakage problems with the Northstar series of engines? I have the 4.0L V8 in mine.

The GM 3.1 and 3.8 had known issues with the intake gaskets. Could leak oil, water, air...and even with low-ish miles. The Northstar motors are totally different designs but I don't know anything about their reliability or problems.
 
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Old 04-28-17, 07:35 AM
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I switched my 2001 4.6l mustang to synthetic at 100k and it never leaked a drop. I did the same with my 2002 chevy blazer for easier winter starting, that thing leaked oil before and after the switch.
 
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Old 05-03-17, 06:36 AM
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UPDATE
When I first posted this a couple weeks ago I had just crawled out from under my car from looking for the source of the leak. I can't see where it's coming from because it's high up--not the pan, filter or crank seals. Anyhow I was due for an oil change and was considering switching back to dino oil because of the many posts I'd seen in the past in motorsport forums about syn oil leaks. I'm now several hundred miles on "high mileage" conventional oil and where I had a trail of oil on the block and spot on the ground it's all now stopped.

Whether syn oil molecularly sneaks past seals or causes them to shrink or dry...or maybe "high mileage" oil has a magic additive that "fixed" my leak doesn't really matter.

If anyone has ever seen a test or study on this I'd very much like to read it. (hopefully not sponsored by Amsoil or any company with a "snake oil" suspicion)
 
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