How long do the effects of high mileage oil last?

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Wondered about this again as I try to whittle down my stash, which right now includes mostly non-high mileage oil. My three vehicles have 140k, 131k and 170k, ranging in age from 12 to 23 years old. None of them leak and I’d like to keep it that way.

I use a combo of HM and non-HM oil in each and do 6 month oil changes in each. Typically, I try do HM every other oil change.

Once an older engine has been fed HM oil and the seals are presumably healthy, what’s the maximum amount of time you’d recommend going away from HM oil? The whole goal is to keep everything supple and not give anything a chance to start leaking.
 
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I don't see how that is even possible to estimate, honestly.

Any legitimate time estimate would have to start with a known condition of a seal and be measured against each decay factor.

Without that, I cant see anything to base a guess on.
 

HawkeyeScott

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I expect to hear mostly the anecdotal. I also wonder if any of the oil companies have ever weighed in on this.
 
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I expect to hear mostly the anecdotal. I also wonder if any of the oil companies have ever weighed in on this.

Cant speak for oil manufacturers but based on the 2 seal OEM's I rep with and doing the failure analysis I would almost bet they have never even considered it.

It would take a battery of durometer testing, chemical analysis and possibly spectrometry to even begin to define all of that and I don't see the world of auto mechanics ever doing it just for a seal so conversely I don't see the oil companies doing it either.
 
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I know some people have a phobia about mixing but any reason you couldn't just mix say 3 qt of M1 AN to 2 qt of M1 EP HM? That of course assumes both are in your stash. Or how about MaxLife with Valvoline Daily... You get the idea. Any drawbacks to a more moderate seal conditioning continuously vs the way you are doing it now?
 
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I found that on my daughters 2005 Honda Civic with 155,000 miles with a semi mid level leak, Pennzoil Platinum has more swelling agents then Mobil 1 HM. I no longer use Mobil 1 in her car.
 
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I understand the question, but I would suggest just use the oldest oil first. If all the oil is roughly the same age, alternating is a good strategy.
 
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What's the worst that can happen? If you keep an eye on the oil level (and driveway) I'd think that'd be the guide.

I have no idea but maybe just try it and see what happens. FWIW I don't use HM at the moment, despite my fleet being all over 150k on the clock. I've used HM in one vehicle a few times but right now I think it's got regular stuff in it.
 

Jackson_Slugger

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You can always use Liqui Moly Oil Saver, which pretty much seems to be the Euro solution to convert regular oil to something like a HM oil...
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Use a HM oil when you see the need. Continue what you are doing until your HM stash is used up. Then use a non HM oil (or continue what you are now doing).
I tried M1 HM 10w-30 in my F150 to stop a rear seal seep and it worked. When the seep stopped I went back to non HM oil. It's been 2 years on non HM oil and the seep hasn't returned.
I'm using M1 HM 10w-30 in the Dodge van for it's other properties and not the HM part. At it's next change it will get non HM oil.
 
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My uneducated ignorant opinion would be not to switch back and forth. Seems like seals wouldn't like being 'conditioned' then 'unconditioned'.
 
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