[almighty]

I bought a 163k mile 03 Corolla and used high mileage synthetic for about a year. I was new to car maintenance and so I thought it was necessary at this mileage. However upon research, some claim high mileage oil will cause leaks early because it causes seals to swell which will make them wear faster. I was considering switching to regular synthetic but some say that switching from high mileage to regular will cause leaks because the seals will shrink. However all of this is debated and it’s hard to honestly know for sure. In your experiences for cars this model, has there been adverse affects from switching from high mileage oil to non high mileage?

 

[torontoguy222]

If it is true that HM oil swells seals then they probably have already swelled from a year of use.

 

[rmyoder]

All three of my cars (2005 Toy, 2007 Cad, and 2012 Honda) get whatever synthetic or semi synthetic is on sale/rebate, and it has been this way since they were new. Sometimes this was HM, sometimes not. Never any leaks or other oil-related issues. YMMV

 

[almighty]

If it is true that HM oil swells seals then they probably have already swelled from a year of use.

worse case scenario, if i switch to regular then it starts leaking, can i just switch back to high mileage and it will stop leaking?

All three of my cars (2005 Toy, 2007 Cad, and 2012 Honda) get whatever synthetic or semi synthetic is on sale/rebate, and it has been this way since they were new. Sometimes this was HM, sometimes not. Never any leaks or other oil-related issues. YMMV

nice, did you ever run high mileage for over a year straight?

 

[Avalon&CamryOwner]

Just switch to regular synthetic. You shouldn’t have any issues. IMO high mileage for seal reconditioning is BS. Like it works, but if you have a leak, replace the seal.

 

[almighty]

Just switch to regular synthetic. You shouldn’t have any issues. IMO high mileage for seal reconditioning is BS. Like it works, but if you have a leak, replace the seal.

"If you have a leak" Will switching from high mileage to synthetic cause a leak, or is that a seal that's already been worn but covered up by high mileage oil? And replacing seals can be a big job depending on the seal, like a rear main seal which would require removing the engine so I want to make the right decision.

 

[Avalon&CamryOwner]

Unless you already had a leak before, switching to regular synthetic will not cause a leak. If anything the seal reconditioning if not needed cause cause more harm than good. Swelling seals is not good for seals. It’s just a band aid solution. But yes it is just covering an existing problem. Most seals are easy to replace. Except for the rear main seal. Plus if the leak is big enough nothing but replacing it is going to help.

 

[rmyoder]

nice, did you ever run high mileage for over a year straight?

I'm not sure. I remember buying four jugs of Pennzoil Platinum 5w30 HM when it was on sale a few years ago, but I don't remember if I used all of it for the same car or not; two of my cars use 5w30 and each gets an oil change about 2-3 times/year. In both cars, the last few changes have been non-HM full syn.

 

[CamPoo]

...However upon research, some claim high mileage oil will cause leaks early because it causes seals to swell which will make them wear faster. ...

I question this research. Show us the evidence where you read this and then we'll talk.

 

[almighty]

Unless you already had a leak before, switching to regular synthetic will not cause a leak. If anything the seal reconditioning if not needed cause cause more harm than good. Swelling seals is not good for seals. It’s just a band aid solution. But yes it is just covering an existing problem. Most seals are easy to replace. Except for the rear main seal. Plus if the leak is big enough nothing but replacing it is going to help.

ok thanks that makes sense

 

[TruckerI5]

You will find out one way or another, report back.

 

[almighty]

I question this research. Show us the evidence where you read this and then we'll talk.

Mobil 1 vs Mobil 1 "High Mileage"

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"

Definitely return. Special seal conditioners work by causing the seals to swell. Fine if the seal have worn.

Swelling a properly fitting seal results in increases lip load. The seal now wears faster then it should.

Also, the swelling is one time deal. Later when the engine starts using the oil, seal conditioning is no longer an option.

"

You will find out one way or another, report back.

will do

 

[CamPoo]

Mobil 1 vs Mobil 1 "High Mileage"

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So someone else's statement (Doug) is the Evidence??? I really doubt oil makers (like Mobil) are making a product, not testing it and blowing folks engines up, really, really doubt that, but hey use what you want. Every engine will still die someday, no?

 

[almighty]

So someone else's statement (Doug) is the Evidence??? I really doubt oil makers (like Mobil) are making a product, not testing it and blowing folks engines up, really, really doubt that, but hey use what you want. Every engine will still die someday, no?

well causing a leak rarely results in fires but it is hard to prove it is due to high mileage oil anyways if that is the cause because it could just be bad seals. the goal is to prolong the life of the engine so i want the less wear done to my seals as possible

 

[Avalon&CamryOwner]

Do

well causing a leak rarely results in fires but it is hard to prove it is due to high mileage oil anyways if that is the cause because it could just be bad seals. the goal is to prolong the life of the engine so i want the less wear done to my seals as possible

Don’t say that. I want my 1MZFE to last forever.

 

[BlueMR280]

It was a long time ago, but I switched from regular oil to full synthetic in my Integra GS-R (when the engine had 155k miles). It didn't cause any leaks.

 

[almighty]

It was a long time ago, but I switched from regular oil to full synthetic in my Integra GS-R (when the engine had 155k miles). It didn't cause any leaks.

this post is about switching from high mileage to non high mileage, not synthetic vs conventional

 

[BlueMR280]

Sorry about that. I actually had never heard that claim/caution about switching away from high mileage.

 

[EspHack]

confusion is usually lack of honesty, these terms are 90% marketing, whatever they claim is probably "true" with a million asterisks, if that

best oil is fresh oil, beyond that, avoid the $3 jug sale

 

[TruckerI5]

Sorry about that. I actually had never heard that claim/caution about switching away from high mileage.

I have heard it, and come across it now and then from mechanics, online that is. The argument is that the additives in the High Mileage Oil helps seals to swell, this can help older engines that may have started to have very small minor leaks, to get more life out of those seals. The argument is that once you use HM oil and the seals swell, over time they take on the shape of the area they are sealing in their swollen state and will hold that shape. When the HM additives are then later removed from the oil such as switching back to regular oil, the seals will over time shrink back down and the leaks will return or if there were no leaks they may now begin to leak because the seal will now be a bit deformed after it shrinks back down as compared to its shape if it was never swollen in the first place. I am sure there is a video out there someplace where someone has done some testing to see if this is really an issue or not.

But I honestly do not know if the HM oil additives cause a healthy seal to swell any larger than it is new or if the additives just "recondition" old seals that may have over time started to kind of dry out/harden and maybe shrink on their own do to age, maybe the HM oil just kind of rehydrates them to plump them back up to something closer to their new condition rather than making them any larger than they ever were. I think I have seen a video not long ago where they took brand new seals and soaked them over time in 2 oils, one with no conditioning additives and the other in HM oil. At conclusion there was absolutly no change in size between the two, So I think it is more about making old hard dry seals more flexible/soft and back to normal size/tension. If that is the case, if you had no leaks before you should not if you switch back to non-HM oil I would think.