Lexus says Synthetic -> Dino not recommended. Why?

[kreativ]

From what I've read, the current synthetic and dino oils are compatible with each other, and you can switch to synthetic and back to dino without any detriment to the engine.

Is there a reason Lexus recommends against doing so?

From Lexus FAQ:

quote:

---

Can I use synthetic engine oil in my Lexus vehicle during its break-in period?

Synthetic oil can be used at the first scheduled oil change. Please note that the use of synthetic oil does not extend the recommended oil change intervals. Please refer to the Lexus Owner's Manual Supplement for further information regarding the proper maintenance schedule for your specific vehicle. If synthetic oil is used after that time, it should be the same SAE (Society of Automotive Engineers) weight specification and meet or exceed the API (American Petroleum Institute) grade specifications listed in the Owner's Manual. If synthetic oil is used, we do not recommend longer oil change intervals. Once synthetic oil is used, it is best not to switch back to petroleum-based oil.

---

 

[Mickey_M]

quote:

---

Originally posted by kreativ:
From what I've read, the current synthetic and dino oils are compatible with each other, and you can switch to synthetic and back to dino without any detriment to the engine.

Is there a reason Lexus recommends against doing so?

---

Ask Lexus:

http://www.lalexus.com/home/contact_lexus.html

http://techinfo.lexus.com/

Switching from synthetic to mineral oils causes problems in only two situations that I am aware of:

1. You're using a synthetic that does not mix with mineral oil. That problem existed around 50 years ago when a synthetic that gelled in the presence of mineral oil was used. I don't think Lexus is referring to that.

2. You use a synthetic that swells seals and then move back to a mineral oil. That could leave you with leaks. Molakule claims it is not a problem. As far as I know it is not a problem with the major brands of Group III and PAO based synthetics, although at least in theory it could be a problem with some esters.

 

[Ray H]

Toyota's cautionary doesn't make sense, nor is the confusion helped by Toyota's lack of any exlplanation for its recommendation. Everything available from the various motor oil formulators stresses that synthetics are compatible with conventionals. (Obviously companies with a vested interest in selling synthetic motor oils, such as Mobil and Castrol would like buyers to continue using their synthetic motor oils, but neither company suggests that ill effects to the engine will occur if the owner changes back - in fact both state just the opposite.) PAOs tend to harden and shrink elastomerics - that's the reason esters were added to them to begin with in order to preserve the seals' flexibility and sealing ability. Conventional motor oils with naphthene (an aromatic) content maintained elastomeric seals' flexibility properties naturally. The very reduced aromatic content in Group II and Group IIIs may benefit or even require a little help from ester addition, though. Going from either Group III or Group IV based motor oils back to conventional (Group II or Group I) should have no negative effects on a Toyota engine - whether it's installed in a Toyota or a Lexus.

 

[SilverGGA@Work]

Many manufacturers say that you have to use the same recommended viscosity grade. Has anyone heard of manufacturers declining engine warranty if someone used say a 0w30 in a car specified for 5w30?

I am fighting over this as my WRX specifies 5w30, 10w30, and 10w-40 in a little oil chart, and I want to use Mobil 1 0w-40 or 5w-40 T&SUV. There is no API certified synthetic that is 10w-40 (except Castrol Syntec which I dislike).

I understand the recommendation is dino based (ie 10w-40 and no 5w-40/0w-40). But wonders if I should just use Mobil 1 5w30/10w-30 and sleep easier at night....

quote:

---

it should be the same SAE (Society of Automotive Engineers) weight specification and meet or exceed the API (American Petroleum Institute) grade

---

 

[ARH_0700]

I was actually wondering the same thing. My G35 also specs 5w30/10w30/10w40 in the manual but I want to use M1 0w40. I guess I will ask my tech next time I bring it in for an oil change.

 

[SilverGGA]

Well, but what the tech says have no weight. He can tell you it is fine but he might have another face when you bring the car in with a broken engine, and he knows there is a reason for him to deny the work.

quote:

---

Originally posted by Twilight_Blue_G35c:
I was actually wondering the same thing. My G35 also specs 5w30/10w30/10w40 in the manual but I want to use M1 0w40. I guess I will ask my tech next time I bring it in for an oil change.

---

 

[Ray H]

Realistically, it's doubtfull using 0W-40 synthetic when 10W-40 is permited would result in a broken engine. There really aren't that many actual oil related failures unless the flow is interrupted and/or the oil is routinely driven to near or total additive depletion. Arguably, 0W-40 would give better cold-cranking performance than 10W-40. Even if the engine manufacturer were to pull a sample for analysis before authorizing a questionable warranty claim, expected viscosity increase from use would probably mask that it started out as 0W-40, anyway. Besides, it's your car, and not mine.

 

[kenw]

several of the early so-called "recommended" synthetic statements were merely a marketing effort by the oil/syn maker. The carmaker gets a great deal on "oil" and the oil maker gets some ad space and prestige. The oil maker even paid for the stickers under the hood....

 

[StanW]

SilverGGA, Royal Purple SAE 10w40 is API approved and is a full PAO Group IV Synthetic.

 

[Audi Junkie]

My guess is that when a Blackstone UOA is pulled by the dealer for a warranty issue, they just go by Terry's good/bad judgment as whether the oil is "serviceable". Visc at operating temp is should only matter as far as mfg recommendation goes. Cold-cranking should be only an issue if it was somehow insufficient. If the dealer accused someone of using a too high CC oil, they could answer "I honestly did not start my car during that cold period". lol