Oil Seal Gasket Leaks Changing to Synthetic Oil

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Is There A Risk of Gasket Leaks or Seal Leaks When Changing to Synthetic Oils?

A former OEM headquarters senior engineer gives detailed answers to common questions about potential engine oil leaks when changing to synthetic oils.

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It’s true that the best high-performance synthetic engine oils can dramatically reduce wear while using less oil, less fuel and costing less money annually.  But, can a change to synthetic engine oil cause gasket or oil seal leaks in your engine?

First, the short summary answer is no: that is a myth. However, the myth is probably based on a special category of synthetic racing oil that is often not compatible with all seal materials.

Additionally, gaskets and oil-seals are two entirely different things.  Gasket leaks are never caused by engine oil. But oil seals are a different story.  

Under certain circumstances synthetic oil can more clearly reveal an existing oil-seal leak, sometimes called a “false seal”.  But that’s rare – somewhere way below 1%.  A far more common result of changing to a true synthetic motor oil is to eliminate oil-seal leaks, and reduce oil consumption.  In fact, AMSOIL synthetics are rigorously designed to be not only compatible, but even MORE beneficial to seal materials than conventional oils.

So, is changing to a true synthetic engine oil more likely help you, or, to cause problems?  There is no need for guessing or rolling dice on your engine’s future.  If you understand what’s happening and what to look for, you can usually decide whether you have a rare case with genuine risk of having an oil leak problem, or whether you can just be another thrilled customer who discovered the secret of AMSOIL.  Below, we’ll uncover the realities so that you can decide for yourself.

Additionally, because gaskets and oil-seals are two entirely different things, we’ll both each of them separately.  Gaskets are an easy subject, so let’s address them first.

Synthetic motor oils cause gasket failure?  (LOL, no, not in this solar system)

Engine gasket kit shows various types of gaskets

A gasket is a thin material placed between two smooth component surfaces, which get strongly and evenly clamped together by bolts or screws.  A gasket is only similar to a “seal” in the sense that it has an engine sealing function.  By design, OEM engine gasket materials are impervious to motor oils of any kind.  Gasket leaks are caused only by mechanical damage to either the gasket or the clamping/sealing surfaces, by improper assembly or improper gasket selection, or by loose or broken bolts.

A few years ago, a respected ASE-certified mechanic recommended to my youngest brother that he should not change his recent-model Cadillac over to synthetic because there was visible indication of very slight “seepage” at a gasket.  He cautioned that installing a synthetic engine oil could cause gaskets to fail – “and a head gasket failure is an expensive repair”.  I shared this with an automotive engineer at GM headquarters, the OEM who designs and makes Cadillacs.  His response nearly dripped with derision: “What does using a synthetic have to do with a head gasket failure!?!  I’d like to hear the logic behind that one!”

Similar wild stories are widespread, shared by “experts” who may or may not be well-intentioned.  Typically the anti-synthetic stories seem to be rooted in either the petroleum oil companies anti-synthetic propaganda years ago (before introducing their own “synthetic”), or from a well-intentioned mechanic who mis-diagnosed the cause of a customer vehicle’s problem.  (I personally know one of these mechanics.  He’s respected in his tiny country-town community – population under 500 – but he has no interest in logically discussing obvious weaknesses in his conclusions.)

However, other motives for bashing synthetics can occur when a mechanic has been paid to work on an engine. Perhaps he has created a small oil leak by not following good practice with gasket installation, or by using cheap replacement gaskets which do not meet the OEM design requirements for that engine application.  In such cases, the mechanic may not want the owner to change to a synthetic oil which might result in a more obvious leak which he would be responsible to repair.  Or perhaps he feels that there is a leak risk from his poor workmanship, such as not replacing torque-to-yield (TTY) bolts as required in order to have proper gasket-clamping force.  In such a case, he might give a caution about synthetics so that he can later blame the use of synthetic oils if a gasket leak develops.

Weak-gasket failures are relatively rare.  But a weak gasket may exist from a manufacturing flaw, for example, or from a borderline engine or gasket design, from damage during the original engine assembly or during engine repair work, or from overpressure caused by engine modifications.  A weak gasket can fail at any time.  But just because that failure occurs a few days/months after changing oil brands does not mean that the oil had anything to do with it.  That’s called “pure coincidence”.

I once had a valve-cover gasket that leaked oil, and after I changed the engine over to AMSOIL it leaked even more.  When I removed the valve cover, I discovered that when a mechanic previously removed it for maintenance that the flat machined sealing surface of the engine had been gouged in that spot: the gouge was a leak-path which had nothing to do with the type of engine oil, but was cleaned out by the synthetic so that it could leak more.  By cleaning the gouge, and simply adding a gel gasket-sealant in the nick area before replacing the gasket, I minimized the leak to a very low level that didn’t cause problems.

What about oil-seals with Synthetic Engine Oils?

First, do you actually have an oil leak now?   This is important because if there is no leak, there is no concern when changing to a high performance Group IV synthetic, or even a pretender Group III petroleum “synthetic”.  The reality in summary?  If there are no oil-drips in the driveway, and if inspection under the vehicle, in the engine compartment and on top of the engine does not show any surfaces wet with oil, then for all practical purposes you have no oil leak to worry about: changing to an AMSOIL synthetic engine oil is risk-free, and nothing but huge advantages. In fact, true synthetic oils are one of the three biggest secrets in automotive maintenance.

There is one caveat in Group V synthetics: a few niche racing oils may have synthetic formulations which are not compatible with all seal materials. Racing engines are built with high performance seals that should be compatible with racing oils, but if not, the oil can start dissolving the seals. This situation is unusual, but it suggests that before you use a racing oil in other than a special-built race engine, you should investigate.  

Further below we’ll define oil-seal leaks in more detail, but first you need a simple background on oil-seals.  Most oil-seals are essentially round pliable rings (made of an elastomer material) which seal around a shaft hole, keeping the oil inside the engine while allowing the shaft to move.  For example, valves slide back and forth inside valve seals, and crankshafts rotate inside the seals.  A “main seal”, “front main seal”, or “rear main seal” usually refer to seals around the main engine crankshaft which transfers all the rotational power out of the engine and into the transmission and wheels.

When an engine runs with petroleum oil, the sludge and varnish deposits that occur (from using petroleum oil in the hot engine) will accumulate around your pistons, rings, seals, valvetrain, and in oil passages.  These deposits on a seal will block the seal material’s access to the engine oil, causing the seal to very slowly shrink and harden from engine heat.  Ironically the same deposits can eventually help to seal older engine seals from the oil leaks which the deposits have caused.  This type of “sealing” from petroleum oil deposits is a sign of invisibly growing problems such as piston ring sticking, sludge deposits in valve covers, oil passages and oil pans which can lead to decreased oil pump capacity output and restriction of critical oil galley passageways over an extended period of time, plus many other issues.

Key point: Most oil-seal elastomers are not designed to function isolated from oil. In fact, most oil seals need continuous oil contact, and are designed to benefit from oil washing in two ways: from cooling effect, and from seal-conditioners in the oil’s additive package.  So these petroleum varnish and sludge deposits are definitely detrimental to the proper function and longevity of your engine.  Removing those deposits and preventing reoccurence is important for long life of every engine, including its oil seals.

AMSOIL cleans piston ringsReality? A good synthetic motor oil is ideal rehabilitation for shrunken seals, and can maintain healthy seals almost indefinitely.  For example, because AMSOIL Synthetic oils are rich with top-quality cleansing detergents, and do not break down to form deposits, these engine oils are able to clean out the engine to restore normal, healthy function and prevent serious further deterioration that often occurs from petroleum oil buildup. These benefits occur throughout the engine, from piston rings to oil passages and oil seals.

The Million Mile Van is a good example: it ran standard oils for the first 68,000 miles of its’s life, and ran the rest of the million miles with AMSOIL synthetic engine oil.  It never had an oil leak.

You may have heard the myth that synthetics cause engine seals to leak. Good synthetic motor oils absolutely do not cause seals to leak, but they may more clearly reveal an existing leak path due typically to one of two conditions:

  1. a failed seal which is in need of mechanical replacement, or
  2. a shrunken seal

Let’s review each condition.

A failed seal is because either the seal lip is worn down, or the seal is hardened and cracked from old age and heat exposure. (But again, most of this deterioration is caused by the seal being isolated from the motor oil, due to sludge and varnish buildup.)  In reality, the “worn down seal lip” is usually more shrunken than it is worn, meaning that rejuvenation is likely able to restore proper sealing. It is true that if you have an antique engine (over 25 years old), and the seals are original, the seal design is usually not as good as modern engines: old seal materials were more prone to cracking when shrunken and hot.  In such cases, although the presence of oil-wet surfaces might mean that you have a cracked seal, the greater problem is that there are likely damaging levels of internal oil sludge and/or varnish which need to be removed in order to preserve the remaining engine life.

A shrunken seal condition is more likely if you have a ten-year “old” engine that has been running petroleum oil for several years. If, for example, it leaks around the rear-main oil seal, then chances are it will initially leak more with a change to a true synthetic oil.  But that synthetic oil change is typically the beginning of better engine health, not the end of the seal’s life or of the engine.  What do I mean by that?  See below, where our engineering answers to these reader’s questions nicely illustrate what most often happens in these situations:

Please note that engines with more than a few years on petroleum oil should be properly converted to AMSOIL to minimize or avoid risks.  This is especially critical if your engine is one of the 4.5 million engines known to have oil sludge buildup problems.  For best results when changing to AMSOIL, we recommend using this easy AMSOIL engine conversion process if your engine is more than two years old or more than 30,000 miles.


Questions and Answers
about Synthetic Oils and Leaks in O-rings and Gaskets:

These e-mailed/posted questions were answered by our degreed automotive engineers.
(None of them are employed by AMSOIL, Inc.)

AMSOIL oils, fluids, filters and fuel additives for cars, trucks, snowmobiles, marine watercraft, farming, construction, offroad and racing applications

 

Q: What about my leaking main seal (for engine oil)?

A:  If it is “seeping” oil slightly, that typically means that it’s got deposits on the other side that are keeping the seal-conditioners in the oil from getting to it, and so it’s drying out and shrinking.

I had that problem – a classic one – on my ’94 Taurus SHO (Super High Output) with the Yamaha 3.2L engine.  It was leaking enough to keep the bottom of the engine and transmission wet with oil, and occasionally put a drop or two on the driveway, with 60,000 miles on it. Now, “everyone” in the national SHO Registry owner’s club seemed to agree that you MUST replace that leaking Yamaha seal, including the top American mechanics who are recognized SHO experts. Because, they said, there was no other option, and it would just continue to get worse.  But I didn’t change the seal.  Instead, after researching the subject more, I just changed to AMSOIL’s 5W-30 (ASL)  because I knew it would probably help. And in the first couple thousand miles, it leaked more. (Right on par, as I expected, due to cleaning the deposits out from around the other side of the seal.) Then over about 5,000 miles that oil leak got smaller and smaller. After 10,000 miles you could barely tell there was a leak. (Typical results of AMSOIL’s superior seal-conditioning performance.) By the time my SHO had 80,000 miles on it, the underside looked like there might have been an oil leak sometime, or maybe one starting, but you sure couldn’t tell where. That was exciting, and impressive, and it saved me a lot of money.  The rear main seal leak was gone – it was cured by AMSOIL engine oil.  And ~100,000 miles later when I sold it, it still wasn’t leaking.

Q: What about my leaking main seal (for engine oil)?

A:  If it is “seeping” oil slightly, that typically means that it’s got deposits on the other side that are keeping the seal-conditioners in the oil from getting to it, and so it’s drying out and shrinking.

I had that problem – a classic one – on my ’94 Taurus SHO (Super High Output) with the Yamaha 3.2L engine.  It was leaking enough to keep the bottom of the engine and transmission wet with oil, and occasionally put a drop or two on the driveway, with 60,000 miles on it. Now, “everyone” in the national SHO Registry owner’s club seemed to agree that you MUST replace that leaking Yamaha seal, including the top American mechanics who are recognized SHO experts. Because, they said, there was no other option, and it would just continue to get worse.  But I didn’t change the seal.  Instead, after researching the subject more, I just changed to AMSOIL’s 5W-30 (ASL)  because I knew it would probably help. And in the first couple thousand miles, it leaked more. (Right on par, as I expected, due to cleaning the deposits out from around the other side of the seal.) Then over about 5,000 miles that oil leak got smaller and smaller. After 10,000 miles you could barely tell there was a leak. (Typical results of AMSOIL’s superior seal-conditioning performance.) By the time my SHO had 80,000 miles on it, the underside looked like there might have been an oil leak sometime, or maybe one starting, but you sure couldn’t tell where. That was exciting, and impressive, and it saved me a lot of money.  The rear main seal leak was gone – it was cured by AMSOIL engine oil.  And ~100,000 miles later when I sold it, it still wasn’t leaking.

Q: “I’m concerned.  I have a lot of miles on my engine, and some people say don’t change to synthetics with high mileage.  Can you explain about Cracked or Leaking Seals in more detail?”

A:  There has been a lot of fear-selling of seal & gasket-leaks in the market, mostly originating from petroleum companies and quick-change oil franchises who get maximum profit from consumers NOT using the superior synthetic oil technologies.  It’s interesting that when a vehicle is new, “they” say that you don’t want to change to a synthetic because of warranty (fear)… and when it’s out of warranty you don’t want to change because now your engine has “higher mileage” and it might (gasp!) develop “problems” if you use synthetics.  It’s pure consumer manipulation: a psychological pickpocketing scam.  Fear is a powerful marketing technique, especially when it’s aimed at keeping you locked into familiar habits with safe, familiar results: it’s easy to tap the fear of unknown risks.

In order to move past baseless fears and discuss the realities to consider, we first need to answer a basic question:

What is “an oil leak”?

An oil leak is NOT a slight discoloration.  If you have a discoloration around a seal or gasket, that is NOT a leak. Unless you have a show-vehicle that will be judged in competition and you are bothered because it won’t clean or it reappears after you clean it, you would be crazy to even think about “repairing” that.  Discoloration spots like this can occur from a single drop or smudge of oil from outside the engine, and this is a common result of normal oil-level checks (a drop or two from the dipstick) and oil changes: when the engine is being refilled with oil, anyone in a hurry or who doesn’t frequently change oil will typically spill a little oil somewhere into the engine compartment, and oil that isn’t completely cleaned up can be blown around in the engine compartment when the engine starts and the fan and belts are turning.

Discolorations never turn into leaks because you change to a high-quality true synthetic oil, like AMSOIL.

When there is slight seepage of oil around a seal, which is common from shrunken seals, it is not a reason for worry when converting to AMSOIL, but is actually a good warning sign that you SHOULD SWITCH to an AMSOIL synthetic engine oil: after a likely period of slightly more seepage, AMSOIL’s rejuvenating reconditioning of the seal will restore proper function, and the leak will gradually diminish to less than originally.  Eventually, it may completely disappear.  This can take up to 15,000 miles depending on the seal material and the condition of the seal. But in our experience, leaks are usually reduced to below pre-AMSOIL levels by the time it’s driven 7,000 miles.

A true engine oil leak is when an engine surface and/or underbody surface area is always wet with oil.

Then the important question is this: where is it leaking from, and how much is it leaking?  If it’s leaking enough to get a large engine surface wet with oil, but it is not dripping in the driveway, or if it leaves a drip every day or two, this is typical of a shrunken and/or worn seal condition.  If you can watch consecutive drips on the driveway, leaving a growing spot, you better check your dipstick weekly because THAT is when you are more likely to have a cracked seal or some other mechanical problem.  IF you have a cracked seal, then anything different that you do with your oil can cause much faster leaking, and we DO NOT recommend that you change to a synthetic oil. Instead, have a mechanic look at the engine to identify the problem and quote a repair: then change to a synthetic after you have repaired the problem, in order to prevent more internal engine damage.

There is some slight risk on old engines with high mileage on petroleum oils, that an oil seal is cracked from being extremely dried out, and is being mostly “sealed” with sludge deposits.  Some feel that because this low risk exists, that they should not switch to AMSOIL Synthetic Engine Oil because a cracked seal will “begin to leak” a lot more. (But if it is not leaking now, then it is probably not cracked!)   However, it is these deposits which are often the primary cause of seal wear and cracking, because they prevent the oil from cooling the seal and prevent the oil’s seal conditioners from keeping the seal soft and lubricated.

Our opinion, as automotive engineers, is that when a slight seal-leak condition exists, it often indicates a high level of sludge and varnish deposits in the engine which are decreasing engine life, and as they continue to build up they are accelerating engine wear and creating an ever-higher risk of rapid or sudden engine failure.  It’s similar to the risk of cholesterol deposits closing off your arteries and causing heart attacks under stress conditions.

If a small oil leak turns into a bad oil leak immediately after changing to AMSOIL, it is likely that the AMSOIL has revealed a cracked seal.  But if a cracked seal leaks badly after switching to AMSOIL, and you have to replace it, it’s also an indication that you’ve dramatically extended your engine life by switching to AMSOIL.  And that’s great!  No-one wants the expense of replacing a seal, but it’s a problem that will only get worse, and it’s cheaper to replace a seal than to replace the engine!

REALITY CHECK – Summary on Seal and Gasket Compatibility:AMSOIL Engine Oils are Devoted to protection

AMSOIL Signature Series synthetic motor oils are made of completely pure synthetic base-stocks, designed and constructed as ideal lubrication molecules, blended with the highest-performance additives available, and are fully compatible with all engine gaskets and seal materials.  In fact, because they are more painstakingly designed than petroleum oils, AMSOIL synthetic oils help maintain seal integrity better, rejuvenate shrunken seals, and extend seal life far better than conventional oils.  However, AMSOIL Synthetic Motor Oils are recommended for use in mechanically sound engines!  Most “leaks” are slight seepage that does not drip oil and is only significant in car-show judging.  If you have a vehicle that is actually leaking oil badly, then it may be best to repair the seal prior to converting to AMSOIL.  And it’s a smart move to replace that seal and switch to AMSOIL – seal problems often indicate high levels of internal engine deposits, and replacing the seals is a lot cheaper than replacing the engine.

Only you or your mechanic can investigate and determine your engine condition and the type of oil leak that may be present in your vehicle engine.  Because of this, there is no way that Ultimate Synthetic Oil or AMSOIL can guarantee leak-free oil seal or gasket integrity of your engine after changing to AMSOIL.  But this information should better equip you to interpret what you see or are told, and make an informed decision about whether you should change to a synthetic oil.


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Easier cold weather starting, improved cold weather pumpability and circulation, smoother engine performance and more horsepower, reduced exhaust emissions, superior wear protection, improved fuel economy, extended engine life, extended starter life, excellent engine cleanliness, long drain intervals, longer spark plug life, reduced engine temperatures, reduced oil consumption, excellent resistance to sludge, coke, varnish deposits (Thermal Stability), reduced/eliminated piston groove sticking, reduced/eliminated valve sticking, superior shear stability, superior resistance to viscosity increase (Volatility Resistance), superior film strength, no more stuck oil filters (using AMSOIL EaO filters), money and time savings.

You will not get any of these benefits with conventional petroleum oil !!!!!

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