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I recently bought a 2001 GMC Savana 1500 Van, with 350-V8 {or 5.7L}, (15 years old) that is Exceptionally Clean with 128,000 Miles on it, Runs Like New and was Garage Kept. It had regular Dino Oil in it, But I changed to Mobil 1 Synthetic oil. It NEVER LEAKED OIL, NOT A DROP on my Driveway, Until I changed to Mobil 1 oil. Now 1,500 miles later, it has a small leak on my driveway...SO, MY QUESTION IS: If I Change Back to regular Dino Oil...Will that leak Stop? Did the synthetic oil shrink my seals and will the Dino oil Re-Swell them to stop the Leak? Can a Mechanic help answer this please. Thanks to all who answer. Please Help.!!!
Changing from dino to synthetic alone is not going to cause a leak. However, if you also changed the weight of oil, like going from a 10w-30 to a 0-30, then yes, the thinner oil could possibly start leaking where the thicker oil never did.
Most likely though, it was just time. At 128k and 15 years old, you've probably got some old seals/gaskets that need to be replaced.
You don't say where the leak is from, but at that mileage and age, it's pretty common for valve cover gaskets to start leaking on a lot of cars.
synthetic oil is more aggressive at cleaning sludge out of an engine, so if you had some sludge plugging a leak, the plug would have been cleaned out, and the leak would then reappear.
synthetic oil is more aggressive at cleaning sludge out of an engine, so if you had some sludge plugging a leak, the plug would have been cleaned out, and the leak would then reappear.
that is likely what has happened, and going back to dino won't stop the leak. Changing the oil more agressively with dino would have done the same.
synthetic oil is more aggressive at cleaning sludge out of an engine, so if you had some sludge plugging a leak, the plug would have been cleaned out, and the leak would then reappear.
I am rather sceptical about the theory that sludge seals leaks.
If the van is exceptionally clean then it should be very easy to go underneath and see exactly where the leak is coming from.
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