Gaskets and High Mileage Oil

Shel_B

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It is said the HM oil swell, expands, or conditions engine seals, but what about gaskets such as valve cover gaskets, water pump gaskets, and timing belt/chain covers. Do these gaskets get oiled enough, or even oiled at all, to benefit from an HM oil?

My limited experience (one car, one oil) suggests that HM oil is of little or no use for some of these leaks and seeps. But I was trying to stop or slow an existing leak, not prevent a leak from starting. So, can an HM oil help prevent gasket leaks?
 
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The more I learn about oil the more i suspect high mileage oil is really more of a marketing thing, similar to "truck oil". All oils contain some amount of seal swelling ability as far as I know.

In the end no oil can save a gasket that's 20+ years old and has been smashed to be brittle and plastic like.
 
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The more I learn about oil the more i suspect high mileage oil is really more of a marketing thing, similar to "truck oil". All oils contain some amount of seal swelling ability as far as I know.

In the end no oil can save a gasket that's 20+ years old and has been smashed to be brittle and plastic like.
Quite possible, I ran HM oil in my old truck for 6 years it never did slow down any leaks.
 
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It is said the HM oil swell, expands, or conditions engine seals, but what about gaskets such as valve cover gaskets, water pump gaskets, and timing belt/chain covers. Do these gaskets get oiled enough, or even oiled at all, to benefit from an HM oil?
It is said ? If you look up the specs. on the oil ratings SL, SM,SN, SP for example there certain requirements and parameters for the oils to meet the specs. Seal swell in one of them. Yes they are well oiled. We also must consider what gasket material is used in the area of the leak.
 
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Valve cover gaskets get splash lubed a bit, but once the material is kaput, nothing will bring it back. Maybe HM helps some gasket materials but not others?

Water pump gasket, are there many engine designs where oil can get to this gasket? outside of that one Ford application, that is. I want to say most designs don't have possibility HM oil helping this gasket.

I think of HM as more of a gimmick. Maybe it helps some people but I think it attempts to garner sales to those who think 75k is a lot of miles on an engine.
 
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What exactly IS the "seal swelling additive?" Chemical of some sort? Some sort of ester additive?

I have used HM oil many times, won't pay extra for it though.
 
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May 3, 2022
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HM oil is typically a bit thicker than non-HM oil
Yep.
I don't know if the way I'm looking at it is legit or not, but I tend to look first thing at density and see if it's relatively high compared to the same viscosity from different brands and normal service oils from the same brand. I can see it affects the base oil viscosity. In theory, it can help minimize leaks a bit more than a lower viscosity base oil. We need help from experienced members because looks like I'm too carried away 😅

I also read somewhere while randomly browsing that HM formulations certainly contain higher esters content in the blend. Maybe it's seal swelling capabilities comes from esters a lot more than a higher viscosity base. But eventually I ain't buying it. Think it's more of marketing gimmick.
 
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I just sold my 17 yo Trailblazer with 130k on it. I started using Pennzoil HM at around 80k. It never leaked a drop or started using any oil. Not sure if the HM played a role, but it didn’t hurt and wasn’t expensive.
 
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I think the question is more like "how do i make my seals last longer" Bc any product that will actually plug leaky seals is very dicey because of where else it can do things.
As far as seal conditioners, i think its more important to just change your oil on time. Seals dry out fast after they get covered in varnish. Thats why all those oil deposit cleaners run the risk of "causing" and oil leak. They clean the varnish and expose the dry cracks that have already formed.
 
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High mileage oil has more sealed condition or if mobil 1 extended performance high mileage or royal purple hmx then it little more ester base oil the. Regular oil . Regular oil minimum seal conditioner because all oil need seal conditioner too. But I will not used high mileage oil $150 K or above I see oil leak .
 
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All my vehicles are 100k+ miles and they all get HM. Knock on wood, I don't have any leaks on any of the 4. I also like the thickest recommended grade so it helps with that too. Also, HM oils are touted as having added cleaning abilities for older, theoretically more varnish-coated engines.

It could still be BS as far as I know. 😁
 
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Jan 4, 2021
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I change oil for my friends vehicles and I use high mileage oil in majority of them and they seem to help. Most of them have told me their oil leaks slowed enough that they no longer needed to top off between changes so it has to be doing something.
 
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If you have leaks, HM is worth trying before doing the necessary repair. After all, HM and non-HM usually cost the same, and using HM will not cause any harm to new or old engines.
 
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