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The real oil seal deal synthetic

*I have been told by the dealers parts man , in conversation with my RC club guys, other forums, you name it , That if you change to a synthetic oil midway on your cars engine that is not a good thing to do because you may have a leak in the engine seals or gaskets.

now the same amount or more mechanics will say the change wont harm anything because if it leaks it was going to anyway no matter or not if you switched to synthetic oil .

what is the real answer the age of the car ,or the manufacturer of the car or what ?

That there synthetic stuff has changed a lot over the years. It’s made from the same oil as the other kind but the molecule has been modified to make it more stable so it doesn’t go bad the same way as the other oil. The rumors of oil seal leaks are not as valid as they used to be. Old wives tales don’t come from old wives these days; they come from people like you and me and we really are a whopping big crowd.

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Conventional oil and synthetic oil are not made from the same stuff. What was the name of the person who told you otherwise? If u come back and say I heard it somewhere, than we know.

Poppycock or BS…take your pick.

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Having owned a bunch of used cars of varying mileage (one as high as 96,000 miles) that immediately got synthetic oil after purchase, I can say “poppycock” to those that claim it will make the seals leak.

I have not owned enough cars for this data to scientifically validate the claim but then neither have any of the folks who told you that synthetic will make your car leak.


That urban legend has been around for years…and no merit to it what-so-ever.


That there synthetic stuff has changed a lot over the years. It’s made from the same oil as the other kind but the molecule has been modified to make it more stable so it doesn’t go bad the same way as the other oil.

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LOL, you get mixed signals from the mechanics you know and the car guys you know, so you come to strangers on the internet, of whose backgrounds you know nothing, for the correct answer?
I’m complimented, but at the same time have to wonder why.

Chemically, dino oil and synthetic oil are the same. The major differences are that synthetic oil is more pure and that its molecules are allegedly more consistent in size. That helps prevent it from being so subject to damage from high heat, such as that involked in turbochargers, and might reduce the effect of molecular "“shearing”, but if your engine (see your owner’s manual) doesn’t require synthetic oil your engine will be perfectly comfortable with dino, synthetic, or a blend. And you can go from one to the other and your engine will never know.

And you can trust that answer because I’m a stranger on the internet! :stuck_out_tongue_winking_eye:


@the_same_mountainbik is right about the oil, If your manual does not call for synthetic you can use regular oil or synthetic and switch back and forth with each oil change. My car does not call for synthetic but states I can use 0-20 or 5-20. I have only found 0-20 in synthetic, I have found 5-20 both regular and synthetic. I use the 0-20 in the winter and 5-20 in the summer. I find the best price for a name brand of the 5-20 and sometimes it it regular - sometimes synthetic. 135,000 miles and so far I do not burn any oil or have any leaks. Change the oil and filter on a regular basis, use the oil that your manual calls for and you will help keep your engine running a long time.

the oddest thing about what my manual recommends .2003 Buick lesabre custom v6 3800.

use 5w30 SYNTHETIC below freezing temperature and
use 10w30 conventional above freezing temperature

Honda has a 0-20 blend. I think they sell it in the parts dept. not sure. my new Honda is specd for 0-20 and this stuff is approved by Honda. is it really 0-20? don’t know. but I do know a full syn oil change at the dealer costs more than a “blend” oil change.

Okay, so you have your answer, written by people who know far more about your engine than the local mechanics and us combined!

Owner’s manual recommendations come from “technical writers” who get their requirements information from the design package developed by the engineers (design, quality, and reliability engineers) and convert them into a user-friendly document. You therefore have the requirement from the guys that designed and tested the engine. Who are we to second-guess them after they performed countless hours of environmental testing, operational testing, accelerated life testing, etc. etc. etc. ?? :grin:
I used to be one of those engineers. I know whereof I speak. :stuck_out_tongue_winking_eye:

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The oddest thing is your not highlighting all the info. Clearly it states you can use either but the syn. may provide better protection. And no where does it say not to use Syn. Anytime.

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Isn’t it amazing how some people will cling to old myths?

You can switch back and forth between conventional oil and synthetic oil as much as you want (as long as your car doesn’t require synthetic oil), and it won’t harm a thing.

I work with a mechanic who insists my car and motorcycles will run better on high octane fuel, even though none of them require it and they all run well on 87 octane fuel. I tried to show him Tom and Ray Magliozzi’s webpage outlining when high octane fuel is required and when it isn’t, and he wouldn’t even read it, saying, “You’ll believe anything you read on the internet.” He wouldn’t stick around long enough for me to explain that Tom and Ray are MIT graduates who ran their own auto repair shop for decades. It shows you how likely we all are to stick to our beliefs, even when presented with evidence that the issue isn’t faith-based, but factual.

My personal take on the synthetic oil issue (for cars that don’t require it) is that you shouldn’t leave it up to chance. If you think your car might benefit from using synthetic oil, why not find out to be sure? If I really wanted to know, I’d get a used oil analysis to find out rather than leave it to guesswork and people’s opinions.

Except it’s not really a myth. Back when synthetics first came out, there were real issues with the difference in the seal swell rates between conventional and synthetics. You could toss orings into the oils and measure the difference in size after enough exposure time. Actually tried it myself. That issue was resolved pretty quickly however and ever since they react similarly (although I’ve taken it on their word and never repeated that test). So I’d say it’s more like clinging to ancient history as if it was still true…


Agreed, it’s not a myth that it used to be a problem, and I probably use the word “myth” a little too loosely.

Yes there was some truth to the myth when Mobil 1 first came to market but it was soon resolved.

As to the synthetic oil in the Buick owners manual, it says to use 0w30 or synthetic 5w30 for temps below -20F.

can I ask why are you saying it may give you better protection . I was under the assumption by facts it is going to give any engine better protection?

yes I have been there and done what yo have done even with model airplane issues in a club with-many members ans till you will get 10 different opinions. Thank you I hear where your coming from