Thread: Oil leak
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Old 12-02-2021, 01:28 PM   #2
fdryer
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Join Date: Jan 2006
Location: NYC
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2003 L-Series 3.0L Sedan
Default Re: Oil leak

History may help but using a thicker weight oil may mask issues. If your oil consumption hasn't changed dramatically including blue smoke exhaust, it may not be any better using thicker weight oil. Oil temperature charts show little difference between a 5w30 and 5w40 oil at low temperatures but do not reflect real world experience such as condensation absorbed in engine oil. You should take into consideration where you live. If in the snow belt region where winter temperatures go below freezing, slower engine turnover may occur along with thicker weight oil and aging battery can contribute to slower engine starting problems. 5w30 oil (regular or synthetic) meets the range of temperatures between -22F/-30C to 50F/13C. Here's one site for info; https://www.hemmings.com/stories/201...y-ratings-mean. 5w is the low temperature rating, 30 is the high temperature rating relative to outside temps. Keeping the 5w rating but going to 5w40 may help for a thicker oil. Oil debates continue with various thoughts. In non snow belt regions, switching to 10w30 or 10w40 might be considered but again, it depends on your knowledge of how your engine turns over everyday when using oil other than 5w30. Additives may be the new sales technique using 'high mileage' oil that may not make any difference other than a placebo effect. Unless proven from a third party well recognized audit, seat of the pants "My car stopped smoking and oil consumption dropped...." opinions may be open for debate.

History - when synthetic oil first appeared, engine manufacturers weren't prepared. Engine seals were mostly paper and rubber. Rubber relied on regular oil for swelling, providing an established seal program used for decades. Synthetic oil does not swell rubber seals so leaks occurred and was a problem to every engine manufacturer and vehicle owner trying syn oil. Crankcase end seals leaked using rubber that didn't swell from syn oil so this new oil was blamed. The engine manufacturers quietly replaced rubber seals with synthetic seals as they caught up with syn oil brought to market. No more seal leaks. Virtually every engine made after syn oil was introduced uses synthetic seals. If I'm not mistaken, when Mobil-1 was first marketed, oil leak complaints were addressed by a corporate response of "syn oil is not compatible with engines using plain rubber seals" with leaks resulting from this incompatibility. Rather than point directly to engine manufacturers switching to synthetic seals, this reply was met with frustration, anger and early blame of syn oil. In reality, syn oil is more viscous, having better lubricity than regular oil so it seeps into nooks and crannies better. Since syn oil doesn't swell non synthetic rubber seals, the shrinking seals allowed oil to leak out. Syn oil also sticks to surfaces longer and doesn't run off as regular oil does. Crucial to protecting cylinder walls on morning startup after overnight resting. Once engine manufacturers switched to synthetic seals (approximately 30 yrs ago), gradual syn oil use showed zero seal leaks. My L300 using syn oil since '05 - zero oil consumption@115k miles. Extended oil change intervals most would find alarming. No engine oil leaks.

Replacing a leaking oil pan gasket, barring physical damage preventing the pan from sealing, may be the best choice to reseal against seal leaks.
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