How do seal conditioners work?

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What exactly do seal conditioners do? If I have a vehicle that is 13 years old and leaks no oil and is not an engine that is prone to leakage, should I use HM? If seal conditioners have no detrimental effects, why do all oils not have them? Should we just start out using HM oil on a new car? Its not a cost issue, since Both HM and regular Mobil 1 and PP cost the same. There has to be a downside....
 
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I was literally going to make this same thread today. If HM oils have no negative effects on brand new cars, then why isn't every single oil a hile mileage formula just sold as normal oil?
 
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Originally Posted By: cheesepuffs
I was literally going to make this same thread today. If HM oils have no negative effects on brand new cars, then why isn't every single oil a hile mileage formula just sold as normal oil?
Cost.
 
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The additive package will have less additive as whole for example less detergent and disperasants in oil to make room for seal swelling additive.
 
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Originally Posted By: Toh1
The additive package will have less additive as whole for example less detergent and disperasants in oil to make room for seal swelling additive.
Please stop.
 
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I'm having difficulty finding sources, and I'm not a chemist, so this may well be a wild guess. I think what happens is over time, heat causes chemical changes in the material of the seal, causing it to loose elasticity and stop hugging the shaft properly, allowing oil to seep out. Seal conditioners are designed to chemically bond to the material of the seal in an attempt to restore some of that elasticity. In cases of minor leaks, the seal may soften enough to hug the shaft again and stop oil from escaping. All oils contain seal conditioners to delay failure of seals, but high mileage oils will contain a higher amount to try repairing seals. How much higher might be a question for the ages (and the chemists and the marketing departments). This doesn't always work, as I actually developed a cam seal leak while using high mileage oil. Whether the oil delayed the leak or prevented it being as bad as it otherwise could have been, I have no idea. Seal could have been weakened years prior by a plugged PCV system and only let go just recently. The other part of a high mileage oil is usually additive formulations meant for dealing with more contaminants, since older engines will tend to have more blowby and more build up inside. Again, how much more cleaning additives and how they differ from the standard version of that oil may vary widely, and may only be known to the people who formulated them. Just from my experience, it's not a magic bullet, but years of using high mileage oils (at similar OCI) have thinned the varnish I can see in the top end of my engine, especially in areas splashed by the cams or submerged in oil. Finally, some high mileage oils are formulated on the higher end of the viscosity range for their advertised weight in an attempt to further reduce oil consumption and provide higher film strength in engines with looser clearances. Not all brands will do this, so looking at the viscosity on the product data sheets will be important here. The downside would be the slight loss of fuel economy, which is important to manufacturers with ever stricter standards to meet.
 
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Specifications. Most true High Mileage oil probably cannot pass current spec's. SN is easy for HM oils to pass but they cannot pass ILSAC, Dexos and many other manufacturers spec's (outside the U.S). Marketing and Competition. I think it was Castrol that came out with the first High Mileage oil in the '90's and that started the snowball for the other companies to follow. Yes. If your vehicle is out of warranty and you want to protect it best, use a HM oil (add pack). I was expecting a gas mileage hit when I went from 5w-30 to 10w-30 HM oil. I actually saw a very slight increase in gas mileage. I would say the gas mileage was more "consistent". Years ago I read an article in, I think, Machinery Lubrication that was condemning the new oil spec's and 20w oils. The article hinted that you should use HM oils after the warranty (or before if you didn't care).
 
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I’ve noticed most HM oils have a fair amount of moly. North of 150ppm. Why this is, I’m not sure. Perhaps it helps with older engines with less precise machining.
 
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There was a medical term in my dictionary that said there is an antidote for a disease, but if you take the antidote and are healthy- you will get that disease. I feel HM oils are for under-maintained vehicles or maybe some that sit for ages with subpar oil in the sump.
 
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Originally Posted By: 1JZ_E46
I’ve noticed most HM oils have a fair amount of moly. North of 150ppm. Why this is, I’m not sure. Perhaps it helps with older engines with less precise machining.
Clearances in engines have been .001 - .003" for decades now
 
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Originally Posted By: cheesepuffs
Originally Posted By: 1JZ_E46
I’ve noticed most HM oils have a fair amount of moly. North of 150ppm. Why this is, I’m not sure. Perhaps it helps with older engines with less precise machining.
Clearances in engines have been .001 - .003" for decades now
In theory they have. Even modern day LS engines are not perfect. Run a hone down an inked cylinder wall with a torque plate fixed and you’ll see what I’m talking about. Same for the mains (not honed after torquing). Surface finish quality is also a lot better these days than it used to be.
 
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There are oil engineers here, that talk out of their rear-end also. What's best for our personal vehicles may not be top-of-the-heap parts. It may not be one single manufacturers five quart jug. It could be a blend of more-than-one. It could be that Premium Plus oil filter that sells for $1.67 at Rockauto and not that Fram Ultra. How we drive - what we drive - how well that engine was put together and what engine's under the hood - plus when we decide to service that vehicle, are what's best for that personal vehicle.
 
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