Will Synthetic Oil Cause Engine Seal Leaks ?
05-06-2013, 09:14 PM
#41
Drifting
I had a 85 corvette that only had 15,000 miles, in 87 I decided to try Mobil 1 10w/30 in less then 5 miles it started to drip out of the rear main. It would drip like every 5 sec. I was really mad after spending all that money for synthetic. I drained it all out and went back to regular oil thankfully the leak stopped. Being only 2 years old and low miles the seals were not old or worn. That is my experience with synthetic so your mechanic is on to something. Most corvette owners change there oil often anyway so why spend the extra money.
10-04-2014, 02:35 PM
#42
I realize this is an old thread, but I wanted to post my recent experience. I built the engine in our '01 Vette several months ago. I used regular Pennzoil 10W30 as break in oil. After the first 500 miles, I switched to synthetic 10w30 and developed a damper seal leak. This engine was bone dry until the oil was changed. It was a brand new Cometic seal that was installed with the correct installation tool. Switching back to Pennzoil 10W30 and will report my findings...
Frank
Frank
10-04-2014, 11:26 PM
#43
Race Director
I had a 85 corvette that only had 15,000 miles, in 87 I decided to try Mobil 1 10w/30 in less then 5 miles it started to drip out of the rear main. It would drip like every 5 sec. I was really mad after spending all that money for synthetic. I drained it all out and went back to regular oil thankfully the leak stopped. Being only 2 years old and low miles the seals were not old or worn. That is my experience with synthetic so your mechanic is on to something. Most corvette owners change there oil often anyway so why spend the extra money.
Last edited by 63mako; 10-04-2014 at 11:29 PM.
10-04-2014, 11:35 PM
#44
Race Director
BTW both of my existing vehicles were changed over to Amsoil lubes throughout @ 1000 miles. Not a drip in any rearend, trans, transaxle or engine seals or gaskets, Zero. Synthetic oil does NOT cause leaks.
10-04-2014, 11:46 PM
#45
Amsoil has protected my motor ....too good ......now I need a new body for my old truck .......20 years old 
.I hate to give up a motor that uses no oil at nearly 215,000 miles ....dang metal body
That's My Amsoil story.
.I hate to give up a motor that uses no oil at nearly 215,000 miles ....dang metal body That's My Amsoil story.
10-05-2014, 10:07 AM
#46
Instructor
Member Since: Nov 2004
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about 3 years ago 1 rebuilt a 67 olds with a 330 bored .030 over all new except for the crank. it was 100 deg day I started it with straight 30 oil with the zinc additive ran it about 1 hr oil pressure was 22 lbs. at idle the high temp light came on I measured 220 deg with a heat gun coming from the engine at the thermostat. the next day was 97 I changed the oil to 15 50 Mobil 1 the temp at the thermostat held at 200 deg I think the oil stays about 38 psi at idle and the high temp light did not come on. the one thing I here different is the starter (I think it is the original) it does not labor. I wish I could have measured the current with the different oils.
10-05-2014, 05:02 PM
#48
Race Director
Part of the proble if Which "synthetic"? A quality Group 4 basestock true synthetic will have an additive to swell and lubricate the seals. an oil labeled "synthetic" could very well be Group 3 basestock which is actually ultra refined conventional oil and may not have the expensive additive for the seals. Big difference. The guys that say "I tried synthetic oil 25 years ago and it made my seals leak so I never used it again" Have no idea what todays synthetics have to offer and have no basis to give any advice on modern synthetics.
10-05-2014, 08:18 PM
#50
Burning Brakes
Regarding the seal/gasket leak theory - when synthetics first came out for automotive applications our engineers had concerns about using it in older vehicles because synthetics do not cause seals to swell at the same rate as normal petro-lubes. They don't shrink them, they just don't swell as much and that had people concerned at first. Remember the warnings about not adding oil to your brake master cylinder? That is partly because it will indeed swell your brake system seals and possibly to the point of catastrophic failure - so, you just don't do it. Conventional oils had that slight swelling/softening effect on powertrain seals/gaskets so the concern was that there could be premature leaks. In fact, at first (25 years ago) there were random reports of premature leaks on vehicles that used synthetic oils from the start. But, the seal/gasket manufacturers - as directed by ever-improving OEM material design spec requirements - long ago addressed this risk in the seals. This one didn't sneak up on anyone. If you think this forum has some good debate, you should have seen it at the engineering level where they had science behind them. Things have long since settled on the side of synthetics, or, again, at minimum a synthetic blend. I personally use a synthetic blend in my '82 to get the best of both worlds and then occasionally add a seal conditioner for peace of mind on my original, 32 year old engine seals.
Hope this helps.
Last edited by Lakeside49; 10-06-2014 at 06:57 AM.
10-07-2014, 11:53 AM
#51
Intermediate
Member Since: Sep 2014
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compromise to syn blend?
This statement is correct. I have been with Ford Motor Company for 30 years and closely associated with our lubricants and chemicals sales & engineering department. There are several reasons why the synthetic oils - or at minimum the synthetic blends are better than what we grew up with. But mainly, if under a microscope you saw how the oil film "shears" under loads you would see that the synthetic oil film is always nearly perfect and the petro oil will always have high and low spots at the molecular level. Recalling the videos we saw, envision a piston ring digging into a cylinder wall on the up-stroke when the ring shears through protective film. It takes more for he syn-lube to "shear" through the film. Another way to envision it, the synthetic oil film always keeps, say, 4-5 micro/nano lubricating ball bearings between your piston ring and the cylinder, but the conventional motor oil may have 4-5 micro ball bearings in one place, and a quarter of an inch later it may have one - the thickness is all over the place. Don't worry about it if you're skeptical - even some dealers are despite seeing the actual test data. There are bigger things to worry about, but synthetic oils have some convincing attributes.
Regarding the seal/gasket leak theory - when synthetics first came out for automotive applications our engineers had concerns about using it in older vehicles because synthetics do not cause seals to swell at the same rate as normal petro-lubes. They don't shrink them, they just don't swell as much and that had people concerned at first. Remember the warnings about not adding oil to your brake master cylinder? That is partly because it will indeed swell your brake system seals and possibly to the point of catastrophic failure - so, you just don't do it. Conventional oils had that slight swelling/softening effect on powertrain seals/gaskets so the concern was that there could be premature leaks. In fact, at first (25 years ago) there were random reports of premature leaks on vehicles that used synthetic oils from the start. But, the seal/gasket manufacturers - as directed by ever-improving OEM material design spec requirements - long ago addressed this risk in the seals. This one didn't sneak up on anyone. If you think this forum has some good debate, you should have seen it at the engineering level where they had science behind them. Things have long since settled on the side of synthetics, or, again, at minimum a synthetic blend. I personally use a synthetic blend in my '82 to get the best of both worlds and then occasionally add a seal conditioner for peace of mind on my original, 32 year old engine seals.
Hope this helps.
Regarding the seal/gasket leak theory - when synthetics first came out for automotive applications our engineers had concerns about using it in older vehicles because synthetics do not cause seals to swell at the same rate as normal petro-lubes. They don't shrink them, they just don't swell as much and that had people concerned at first. Remember the warnings about not adding oil to your brake master cylinder? That is partly because it will indeed swell your brake system seals and possibly to the point of catastrophic failure - so, you just don't do it. Conventional oils had that slight swelling/softening effect on powertrain seals/gaskets so the concern was that there could be premature leaks. In fact, at first (25 years ago) there were random reports of premature leaks on vehicles that used synthetic oils from the start. But, the seal/gasket manufacturers - as directed by ever-improving OEM material design spec requirements - long ago addressed this risk in the seals. This one didn't sneak up on anyone. If you think this forum has some good debate, you should have seen it at the engineering level where they had science behind them. Things have long since settled on the side of synthetics, or, again, at minimum a synthetic blend. I personally use a synthetic blend in my '82 to get the best of both worlds and then occasionally add a seal conditioner for peace of mind on my original, 32 year old engine seals.
Hope this helps.
10-07-2014, 12:31 PM
#52
Le Mans Master
Again, synthetics do not cause leaks. 63mako is correct that most US synthteics are NOT a true group IV synthetic but a III+ highly refined conventional oil, including most Mobil 1 grades EXCEPT Mobil 1 0W-40 European Formula and Porsche Spec 5W-50 which are TRUE group IV synthetics. Most US group III+ "synthetics" are really just highly refined dino oil so their should be no issue using these "synthetics". I use Mobil 1 0W-40 Euro Formula (Group IV) in all my cars and None leak...including my 10 C6 Z06 (switched from Mobil 1 5W-30), 2012 Lexus IS 350 F Sport (switched from Mobil 1 5W-30), 2001 Pontiac Grand Prix-165,000 miles, and my 2008 Chrysler 300 3.5L-120,000 miiles-None leak! My 78 C3 with the just rebuilt L-82 355 will be switched to Mobil 1 0W-40 euro formula (roller cam) soon from conventional Driven 15W-50 since the breakin is over. Even my lawn tractor and generator use Mobil 1 and they don't leak. If these real world examples are not enough evidence that oils do not cause leaks but weak or bad gaskets do, I really don't know what else to say......
Last edited by jb78L-82; 10-07-2014 at 07:37 PM.
10-07-2014, 02:23 PM
#53
Pro
Good comments here. The base stocks can cause seal shrinking or swelling so must be balanced to favor slight seal swelling to keep seals and gaskets from leaking. PAO and ester base stocks must be combined so the additives will stay dissolved in the base stocks. Newbies to the synthetic oil market did not balance base stocks properly and while they enjoyed some of the benefits of synthetics, unfortunately the blend was out of balance and the base stock caused seal shrinkage and oil leaks. That is where some of the experience with synthetics causing leaks originate from...
05-12-2016, 06:48 PM
#54
Informative thread from 2013. Now it is 2016. At a number of popular discount auto stores plus Walmart, I found that standard organic oil (like 10-30W) is not priced practically at the price point of popular synthetic oil. It is a no brainer now to use purchase popular quality synthetic oils.
Top Five Synthetic Oil Myths Debunked:
Myth: Synthetic oil is fake.
Busted! Synthetic oil is derived from natural base oil.
Hayek: Just the word synthetic and the connotation it has with consumers leads them to believe that synthetic oil is a non-natural, man-made product. For example, people look at conventional oil like wool and synthetic oil like polyester. The truth is, synthetic oil is a natural product derived from base oil.
Myth: Using synthetic oil means changing the oil less often.
Busted! While it’s one purpose of synthetic oil, be careful going longer between oil changes.
Hayek: Because car manufacturers have tested and tailored their engine technology around how the engine needs to perform, it’s not as easy as using synthetic oil and ignoring the manufacturer’s recommendations.
Falender: All automotive manufacturers have directions written out as to what the consumer should be doing. It’s important that consumers follow the manufacturer’s instructions.
Myth: Using synthetic oil means better fuel economy.
Busted! Many factors effect fuel economy.
Hayek: Some people think that using synthetic oil means better fuel economy because it’s thinner oil. That is not true. The fact is when you look at 5W-20 conventional oil and 5W-20 synthetic oil, they have very similar viscosity levels. Fuel economy is derived more from changing viscosity grades than it is from switching from a conventional to synthetic motor oil.
Falender: A lot of things influence fuel economy, but one of the main things is a clean engine. When you go to buy a new car, there is a sticker on the window that tells you the miles per gallon that specific car is expected to get. What a lot of people don’t realize is that mile per gallon estimate is for a perfectly clean engine. The minute you drive off the lot with low-quality motor oil, your engine starts to get dirty, and you begin losing fuel mileage. While synthetic oil doesn’t always mean better fuel economy, it can lead to a cleaner engine, which results in more miles for your money.
Myth: All synthetic oil is better than conventional oil.
Busted! Not all oils are created equal.
Hayek: Just because an oil is synthetic doesn’t automatically mean its better than all other conventional oils.
Falender: Synthetics tend to get lumped together. Don’t assume that every synthetic does the same thing.
Myth: Synthetic oil is always thinner.
Busted! Not always, just because it’s synthetic oil doesn’t mean it’s thinner.
Hayek: The truth is 5W-20 conventional or synthetic oil are banded in certain areas to make them 5W-20 oil. It’s a generalization that all synthetics are thinner oils.
Top Five Synthetic Oil Myths Debunked:
Myth: Synthetic oil is fake.
Busted! Synthetic oil is derived from natural base oil.
Hayek: Just the word synthetic and the connotation it has with consumers leads them to believe that synthetic oil is a non-natural, man-made product. For example, people look at conventional oil like wool and synthetic oil like polyester. The truth is, synthetic oil is a natural product derived from base oil.
Myth: Using synthetic oil means changing the oil less often.
Busted! While it’s one purpose of synthetic oil, be careful going longer between oil changes.
Hayek: Because car manufacturers have tested and tailored their engine technology around how the engine needs to perform, it’s not as easy as using synthetic oil and ignoring the manufacturer’s recommendations.
Falender: All automotive manufacturers have directions written out as to what the consumer should be doing. It’s important that consumers follow the manufacturer’s instructions.
Myth: Using synthetic oil means better fuel economy.
Busted! Many factors effect fuel economy.
Hayek: Some people think that using synthetic oil means better fuel economy because it’s thinner oil. That is not true. The fact is when you look at 5W-20 conventional oil and 5W-20 synthetic oil, they have very similar viscosity levels. Fuel economy is derived more from changing viscosity grades than it is from switching from a conventional to synthetic motor oil.
Falender: A lot of things influence fuel economy, but one of the main things is a clean engine. When you go to buy a new car, there is a sticker on the window that tells you the miles per gallon that specific car is expected to get. What a lot of people don’t realize is that mile per gallon estimate is for a perfectly clean engine. The minute you drive off the lot with low-quality motor oil, your engine starts to get dirty, and you begin losing fuel mileage. While synthetic oil doesn’t always mean better fuel economy, it can lead to a cleaner engine, which results in more miles for your money.
Myth: All synthetic oil is better than conventional oil.
Busted! Not all oils are created equal.
Hayek: Just because an oil is synthetic doesn’t automatically mean its better than all other conventional oils.
Falender: Synthetics tend to get lumped together. Don’t assume that every synthetic does the same thing.
Myth: Synthetic oil is always thinner.
Busted! Not always, just because it’s synthetic oil doesn’t mean it’s thinner.
Hayek: The truth is 5W-20 conventional or synthetic oil are banded in certain areas to make them 5W-20 oil. It’s a generalization that all synthetics are thinner oils.
05-13-2016, 04:23 PM
#55
Pro
Some synthetics are synthesized from natural gas (methane), so stating they are derived from natural base oils is true for some synthetics but not others. Lots of things to clarify or rebut here, but I'll let others chime in.