Does full synthetic really cause leaks?

Rae

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Hello, I've been trying to educate myself on automotive oil some and I remember reading a lot a few years ago on these forums that full synthetic oil would cause oil leaking. I don't remember all the circumstances, some I believe were around oil additives such as Auto-RX but others talked about if you start using synthetic you could never successfully go back to dino oil. I've almost completely read through the Oil University on the website here but it hasn't really answered this particular question (although it's been extremely informative). I'd love to hear information about why people might say that synthetic oils would cause leaking. The Oil University talked highly of synthetic so I'd really like to understand this. I want to do the best for our vehicle and it would seem synthetic is on that list. But I need to get out the fear of causing leaks! Looking forward to your replies (even if you point me to other articles, threads or links). Thank you. :-)
 
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It can expose leaks in bad seals/gaskets that are crudded it.. by cleaning them. It wont cause leaks in any engine in good condition.
 
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no, conventional and synthetics are completely compatible. Most good conventionals contain some amount of synthetic base stocks as well, especially the 20wt oils. you can switch back and forth on every oil change if you want. The exception would be as Rand stated above ^
 
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It leakys easier. It really depends on the condition of your seals. I drive a 19 year old car. No leaks in my car even with synthetic. Altho I wouldn't dream about putting it in my '02 Silverado. Also its safe to go back and forth between synthetics. Synthetics of 20-30 years ago are ancient tech compared to modern day synthetics.
 
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Originally Posted By: Rand
It can expose leaks in bad seals/gaskets that are crudded it.. by cleaning them. It wont cause leaks in any engine in good condition.
Right. I have switched two vehicles from dino to syn above 90k miles. Both had a bit of a leak, which went for about 3000 mikes then stopped and never leaked again. The dino crust left from too infrequent dino oil.changes by the previous owners had formed a barrier that kept fresh oil from the seal, which dried out somewhat. Once the synthetic cleaned the crust, it took awhifle or the seal to get recondituoned and start sealing again. Or so my research indicated.
 
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Originally Posted By: 3800Series
I drive a 19 year old car. No leaks in my car even with synthetic. Altho I wouldn't dream about putting it in my '02 Silverado...........
Why not ? Been using M1 15w-50 in many different classic cars for the last 19 years, most of them made over 50 years ago. Some of them have fresh engines, some of them have never been apart and have over 200,000 miles on them. My experience are the same as mentioned earlier, a good synthetic oil will recondition a dried seal, sometimes enough to slow down or stop a leak. It certinly won't cause a good seal to start leaking. Just google synthetic oil myths. Z.
 
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Originally Posted By: zray
Originally Posted By: 3800Series
I drive a 19 year old car. No leaks in my car even with synthetic. Altho I wouldn't dream about putting it in my '02 Silverado...........
Why not ? Been using M1 15w-50 in many different classic cars for the last 19 years, most of them made over 50 years ago. Some of them have fresh engines, some of them have never been apart and have over 200,000 miles on them. My experience are the same as mentioned earlier, a good synthetic oil will recondition a dried seal, sometimes enough to slow down or stop a leak. It certinly won't cause a good seal to start leaking. Just google synthetic oil myths. Z.
Silverado has 340k miles. And leaks even with high mileage. Iv only tried synthetic in it once and it took about a quart every 300 miles. Not worth it. I never said anything about synthetic myths. I know it depends on the seal/gaskets of the engine but at the rate it loses it its not worth it. $8 every 300 miles or $3 every 1k-1.5k miles. Transition went out 30k miles ago and already starting to jerk again. I don't know now much life is left in the truck so I'm more then happy using the cheap stuff. I use synthetic in my new car (new to me at least) since it only had 91k miles on it when I bought it earlier this year. It has plunty of life left so I don't mind spending more on it.
 

Nick1994

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Seeing as how my car has run synthetic from the factory all the way up to its current 162,000+ miles and has never, ever, leaked a SINGLE drop I would say it's safe to say that no, synthetic oils do not cause leaks. They can however open up an existing leak.
 
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I have to agree: syn could expose pre-existing issues, but in an engine with few (if any) issues, you'd be well-suited to run it. That is, granted you're in the runnings for an extended OCI, to extract a good value out of the oil, considering the price differential. "Dino", such as it is, provides a great value IMO even if you're wanting a shorter OCI (3K or so). I run synthetic because I like the add-pack and overall performance of the particular one I use, for my application: QSUD 5w30.
 
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Cause? No. Exacerbate an already existing leak on a car previously using conventional oil exclusively? Maybe. But I also believe that an oci neglected vehicle, switching from a cheap conventional with a poor additives pkg to one of the major brands using correct oci, could do the same.
 
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Originally Posted By: 3800Series
............ I don't know now much life is left in the truck so I'm more then happy using the cheap stuff.
heck, you'll probably get to 500,000 miles without too much effort before the old work horse gets put out to pasture. If money was no object (wouldn't that be nice) it would interesting to see how many oil changes of synthetic oil it took before the leaking slowed. Z
 
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I have a 99 Dodge Caravan that used conventional oil most of it's life. I put some synthetic oil in it 2 years ago and it had a small oil leak from the head gasket at the time. The leak became very large and I have not been able to stop it from leaking ever since. "Stop leak" additives to not work. There is a tray under it in my driveway right now. I will never change from conventional to synthetic ever again in an older vehicle.
 
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All vehicles I've owned from new since 1996 and used syn blends and full synthetics from day one have never had an oil leak from using syn blends or full synthetics. If you have a neglected conventional oil change engine then maybe you'll get "leaks" at first when changing to synthetic. Robert
 

Rae

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Fantastic...absolutely fantastic! Thank you all so much for taking the time to reply. What you're saying makes complete sense and I'm so happy I asked this question. The properties of oil are quite fascinating. The fact that a full synthetic can expose a leak, then clean the crud and eventually recondition the gasket is completely amazing to me. You've pretty much convinced me that we should plan to switch to full synthetic in the vehicle were looking to purchase. I think it will be a good fit. I have questions about the specifics of that but I think a new thread would be more appropriate for keeping everything on topic and easily found. Again I can't thank you all enough for sharing your knowledge and experience with me.
 
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Originally Posted By: WobblyElvis
I have a 99 Dodge Caravan that used conventional oil most of it's life. I put some synthetic oil in it 2 years ago and it had a small oil leak from the head gasket at the time. The leak became very large and I have not been able to stop it from leaking ever since. "Stop leak" additives to not work. There is a tray under it in my driveway right now. I will never change from conventional to synthetic ever again in an older vehicle.
Why not just get the leak repaired instead of spending money on additives, etc.d. The right fix is generally the better choise. Z
 
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Yes, it can cause leaks primarily where the oils are ester based oil, as ester based oils can over swell seals. When you stop using the ester based syn oils the seals can shrink thereby causing leaks.
 
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Originally Posted By: zray
Originally Posted By: WobblyElvis
I have a 99 Dodge Caravan that used conventional oil most of it's life. I put some synthetic oil in it 2 years ago and it had a small oil leak from the head gasket at the time. The leak became very large and I have not been able to stop it from leaking ever since. "Stop leak" additives to not work. There is a tray under it in my driveway right now. I will never change from conventional to synthetic ever again in an older vehicle.
Why not just get the leak repaired instead of spending money on additives, etc.d. The right fix is generally the better choise. Z
It would cost more than the vehicle is worth to me. Not long for the scrap yard.
 
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I have an '85 KZ1100. When I put Synthetic in it, it leaks out from the head gasket and base gasket. When I put conventional oil in it, it does not leat out through the base and head gaskets. This phenomenon is repeatable. YMMV.
 
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Originally Posted By: Rae
Hello, I've been trying to educate myself on automotive oil some and I remember reading a lot a few years ago on these forums that full synthetic oil would cause oil leaking. I don't remember all the circumstances, some I believe were around oil additives such as Auto-RX but others talked about if you start using synthetic you could never successfully go back to dino oil. I've almost completely read through the Oil University on the website here but it hasn't really answered this particular question (although it's been extremely informative). I'd love to hear information about why people might say that synthetic oils would cause leaking. The Oil University talked highly of synthetic so I'd really like to understand this. I want to do the best for our vehicle and it would seem synthetic is on that list. But I need to get out the fear of causing leaks! Looking forward to your replies (even if you point me to other articles, threads or links). Thank you. :-)
Most oil certifications, especially the API SN/RC (Resource Conserving) specification and also the API CJ-4 specification, specifies elastomer compatibility in terms of seal swelling, hardness change, strength change, etc. Regardless of the primary base oil used, other base oils (such as Group V) and additives are added to make sure that your seals are safe and certifications are met. This is the long answer. Short answer is no, synthetic oils include seal swellers and other seal additives just like any other oil and they are no less safe on your seals than any other oil. Therefore, synthetics causing leaks should be your least concern to say the least.
 
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