Synthetic oil dries out seals.

[DGXR]

Replace "a synthetic oil" with "a non-HM oil" and the quote would make more sense and possibly be more accurate.
I am baffled by the whole notion of engine oil drying out a seal... wat?

 

[2000Trooper]

Let me ask this, synthetic oil or not. I have a 2016 Tacoma with 150k miles. I recently had to do some engine work on it that required the valve cover and timing cover to come off. The engine has o rings that seal oil circuits between the block & timing cover, timing cover and pick up tube, valve cover and the head. I replaced all these o rings however the old ones were hard as a rock and I doubt would have sealed properly if reused.

With that said what’s the definition of dried out seals? Is this how seals normally behave or is this a biproduct of today’s formulations?

 

[4WD]

Aren’t most seals Silicone based instead of rubber nowadays?

If not Viton - I always had GM seals wick a bit but not put oil on the driveway - just some funk when mixed with dirt underneath …

 

[paulo57509]

Synthetic engine oil dries out seals?

 

[SumGuy]

I don't know if this is an equivalent sitution - talking about differential oil vs engine oil - but back when I was looking at doing my first differential oil changes in my '00 Chrysler 300M (V6 FWD with separate oil sump for the differential) there was mention back in the '05 - '07 time frame of a Toyota TSB that warned not to use Toyota brand synthetic gear oil in 2003 Tundra (or Sequoia?) because it would cause the differential seals to leak. The sources for this as best I can find today are references to this document:

Toyota TSB DL00303 — 2003 Sequoia
Toyota TSB #DL00303. 2003 Toyota Sequoia. Affected Component: POWER TRAIN. Date Published: OCT 01, 2003; NHTSA TSB #: 10004512. TSB Document.

I can't find a downloadable / readable version of that document, but if it exists and it is what I claim it to be, then there is something to the idea that synthetic oil (albeit gear oil) can impact seals on not-necessarily-antique vehicles.

 

[MolaKule]

then there is something to the idea that synthetic oil (albeit gear oil) can impact seals on not-necessarily-antique vehicles.

There is only one differential seal I am aware of and that is at the Pinion Bearing.

I have never seen synthetic lubricants do anything but increase the pliability of an elastomeric seal.

 

[SumGuy]

There is only one differential seal I am aware of and that is at the Pinion Bearing.

I have never seen synthetic lubricants do anything but increase the pliability of an elastomeric seal.

The TSB that I mentioned above would either confirm or deny your observation in an authoritative way. Perhaps there is someone here that can actually navigate the interwebs to obtain it.

 

[KrisZ]

How can a seal “dry out” when it is being constantly submerged in oil on the wet side? I’ve yet to pull a seal out that would be dry.

They do however degrade their elasticity and become quite hard. However I think that is more of a function of time and heat cycles than the type of oil they’re exposed to.

 

[Bill7]

This quote came from a respected long time member on another automotive forum I frequent. No use trying to clarify since it would result in an ugly dog pile for insinuating the esteemed member wrong. Some myths just won't die.

Would that quote only apply to Group IV PAO based synthetic oils? All non PAO synthetic oils shouldn't shrink engine seals.
Group IV Ester based synthetic oils actually act like a high mileage oil since Ester naturally swells/enlarges engine seals.

 

[SumGuy]

If there is a downloadable version of Toyota TSB #DL00303 then I can't find it.

However, I did find a very active thread about it, circa 2003, here:

Rear axle seal leaks caused by syn. gear oil

www.tundrasolutions.com

That thread centered around this TSB and people claiming this or that oil leaked or didn't leak in their Toyota Tundra.

Someone there did contact Toyota and pressed them for details, and this was the best answer they got:

==============
According to TSB DL003-03 Toyota Genuine Synthetic Differential Gear Oil (P/N 00289-75140) cannot be used in 2000-2002 Tundra vehicles and 2001-2002 Sequoia vehicles. The rear axle oil seals are not compatible and will leak if synthetic differential gear oils are used.

Toyota does not have a position regarding the use of non-Toyota Genuine Synthetic Differential Gear Oil as we do not require its use. If you do use synthetic gear oil Toyota recommends that you do not switch back and forth between regular and synthetic and that you research its compatability with the maker.
===============

Toyota did not want people using Toyota Genuine Synthetic Differential Gear Oil in their Tundra and Sequoia vehicles because "The rear axle oil seals are not compatible and will leak if synthetic differential gear oils are used."

Toyota went out of their way to say they are only making this claim in regards to their own synthetic oil, and no-one elses. Which naturally left the peanut gallery with more questions than answers - was it something specific about the base oil that Toyota uses? Was it an additive that caused seal problems?

Along the way some people wrote about different chemistries involved in seals and how that could or does play a role. I note the following comment near the very end of that thread:

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In regard to synthetic oils, Mobil 1 is made from polyethylene glycol. This oil is rarely safe to use because of incompatibility issues with seals. However, Amsoil is made from a Diester, which is a vegetable base and is quite compatible with all your toyota seals. You won't have any issues if you use a Diester based synthetic oil.
=============

Was that true 20 years ago? Is it still true today? Does the basic chemistry claim in that statement hold water? Is there any relavency with engine oils (a reminder - this was about differential oil).