If a car burns or leaks oil, will synthetic make it burn/leak more?

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I know Synthetic oil won't make the problem worse, but say you had a constant leak where you leaked... oh, say, a quart every 3000 miles using dino oil. If you ran synthetic would you still burn a quart every 3000 miles or would it be more? If more, why?
 
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Well, for starters, a quart every 3000 miles is certainly not a significant leak, if it is really a leak. The auto manufacturers consider using a quart of oil in 800 miles or more to be "within acceptable tolerances". In the situation you describe, I would expect oil consumption to decrease with a change to synthetic.
 
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I would say that it really depends on the engine and it's condition. In general, synthetic shouldn't make it leak more, but if, say, a rear main oil seal is weeping oil because it's worn, the "penetrative" ability of a synthetic may make it weep more. This may well apply to other seal as well. Additionally, some synthetic oils may be of a lower viscosity than an equivalent grade dino, which may allow the oil to get around a weak seal at a greater rate. Another situation may be that a worn seal is compromised with "dirt/debris" and if the synthetic cleans it out, it may leak more. Or, the opposite may happen. A good seal may be compromised by "dirt/debris" and the synthetic oils may clean it out and the seal might start working more effectively. As far as oil burning, I guess some of the same conditions stated above may apply in addition to the NOACK of the oils in question. So as I stated earlier, it all kinda' depends. [ August 12, 2004, 02:20 PM: Message edited by: 427Z06 ]
 

Logik

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Does synthetic oil have "slipprier" molecules or anything like that? Are these uniform molecules smaller than dino oil's molecules?
 
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As a followup, as long as there's oil in the cylinder that has to get burned up... which burns better, dino or synth? Which harms the combustion more (pinging/lower octane, plug fouling, etc.)?
 
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this is just one data point on one car: 97 Saturn SC1 110,000 miles no visible leaks various 5W30 petros: 1qt/1000 miles Mobil 1 0W40: .25 qt/3000 miles (and counting)
 
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Burning a qt in 3000m isn't bad - leaking it is substantial, and messy. As to synthetics leaking more: right or wrong, theories, science, arguments, etc. notwithstanding... I have found in a lifetime of auto repair that yes, you will occasionaly get an increased, or new leak, when changing to synthetic oil. I've seen seal leakage start, valve cover gaskets and side cover gaskets squish out, and seepage from every sealed orfice/gasket, when there wasn't a problem before. I've seen the same type of things when Slick 50, or any number of the newer additives are used, as well. I use synthetic oil in my personal cars,BTW. I'm just saying this is the way it is, and I have a lot of miles in the business.
 
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In my cars that I thought burned oil due to engine issues, the problem was actually the crappy dino oil. When I switched to top-grade synth, consumption was cut in 1/3. Blow-by will cake ring packs up and reduce overall compression too. As far as leaks go, normal thick dino oil is your best bet. 15w-40 dino offers good consumption and no issues with extra leakage. Delvac is my favourite.
 

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Logik,
quote:
Does synthetic oil have "slipprier" molecules or anything like that? Are these uniform molecules smaller than dino oil's molecules?
Here is a thread that might help: http://theoildrop.server101.com/ubb/ultimatebb.php?ubb=get_topic;f=4;t=000356 Also see other articles in "Science and Technology of Lubricating Oils and Additives."
quote:
As a followup, as long as there's oil in the cylinder that has to get burned up... which burns better, dino or synth? Which harms the combustion more (pinging/lower octane, plug fouling, etc.)?
Synthetic oils leave fewer deposits. There two reasons. When synthetic base oil volatizes, it has little residue to leave since the molecule are uniform. Synthetic base oils burn off at much higher temperatures than do mineral oils. Secondly, synthetics require fewer of the additives that contribute to ash formation and deposition. [ August 12, 2004, 09:35 PM: Message edited by: MolaKule ]
 
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