Which kind of seal material are HM oils for ?

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Jan 30, 2007
Clovis, CA
<span style="font-family: 'Verdana'">Obviously paper or cork is not going to respond to seal conditioners or swellers, but what about neoprene or silicone seals; is that the material that HM oils are intended for? </span>
After 2000 with GM sealing problems with 60° V6 . VITON was preffered material along more durable Sealers impregnated Silicone & such . Nowadays all industry use much better Materials . As far as HM PCMO don't need them in modern blocks . My 2 cents
Originally Posted By: dlundblad
I would say neoprene for sure. I had a rear main seal leak that M1 HM 10w30 stopped.
M1 HM swelled that seal right up!
Originally Posted By: Trav
Many seals used in engines today are very chemical resistant FFKM or Teflon. HM oil will not have much of an effect on these materials, the more these materials are used the more of a marketing gimmick HM oil becomes.
Very true.
Originally Posted By: LEADED
Nowadays all industry use much better Materials. As far as HM PCMO don't need them in modern blocks . My 2 cents
Yes, older rubber formulations, like neoprene, just don't see much engine use anymore. Maybe in "el Cheapo" small block chevy gasket kits they still do?
Originally Posted By: CT8
Marketing works
Extra ingredients added to oil in attempt to fix problems = less oil. Marketing or not, seal conditioners work. I've personally witnessed at least 2 automatic transmissions with obviously worn seals straighten right out with "Trans-X" which is the king of seal conditioner overdose. I'm not sure it's a good idea to add a LITTLE Trans-X to engine oil, but I'm sure someone's thought of it.
High Mileage oils use to be a thick for grade oil, with extra seal conditioners (which are in regular oil anyway - but to a lesser amount) and often with elevated ZDDP levels (API SL) for extra wear protection. But now with many insisting on only using API SN oils, the ZDDP zinc levels have been reduced to regular ILSAC amount, and the seal conditioners don't work on many modern seal materials. So what you are left with is a slightly thicker oil, with a big font HM on the label. Strangely enough HM oils have never been popular in Australia, we simply step it up a viscosity grade as the car ages.
Rear main seals will be silicone because of the higher heat, front and cam seals viton or what ever. I know a silicone seal will swell in kerosene, so maybe they will work better on a rear main than other seals. I hope so, my rear main leaks.
Teflon based is also common for rear main seals now, you know you have one when it comes with an installation sleeve. They are finicky to install but work well and leave no groove in the crank after long use, <span style="text-decoration: line-through">swellers</span> conditioners have no effect on them.
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