Oem spec viscosity question.

[aquariuscsm]

My car`s FSM specs all oils from 10W30-20W50. It lists no mono grades or 5W grades,only 10W,15W,and 20W. The USDM versions of my car came with a sticker under the hood that says "Under 70F 10W30,Over 70F 10W40". I`m wanting to use *mid* weight oils from now on. I`m currently using Mobil 1 10W40 HM and my car`s running the best it ever has on this oil. Smooth,responsive,and silent. Seems 40 weight is my car`s "sweet spot". Made me realize how much a 50 weight was slowing it down. How well would a 5W40 (ex-5W40 Synpower) work in my car? Should I just ignore the 5W rating even though it`s not listed in the FSM? I have a case of Synpower 20W50,and I`m going to swap it either for Synpower 5W40,Royal Purple 10W40,or Mobil 1 10W40 HM.

What`s the consensus?

 

[HTSS_TR]

If your 300ZX likes 40 weight I would exchange Synpower 20W50 to 5W40.

 

[fdcg27]

It may be that there were no 5W-40s back when the car was new.
Either that, or the dual rated 5W-40s were too rare for Nissan to even consider them.

 

[CATERHAM]

I'd try M1 0W-40.

 

[aquariuscsm]

I went by there,and they don`t have Synpower 5W40 anymore,not even a spot for it. They do have RP 10W40 for the same price everyone else sells it for (agreement with RP maybe?),BUT,their M1 is $9.00 a quart! What the heck do they think they`re doing charging nine bucks a quart for M1?

 

[aquariuscsm]

I just got back from Advance. I originally paid $4.99 a quart for the Synpower 20W50. I swapped it out for Mobil 1 10W40 HM (they price matched Oreilly`s price for me).

Anyone who`s wondered about M1`s HM oils and considered using it,I say go for it! It`s the smoothest running oil I`ve ever used! As long as I can still get it cheap (Walmart sells it for $23 per 5-quart jug here),I`ll use it for the life of the car,or any other cars I own from now on.

 

[AEHaas]

My thought is that you can ignore the specifications from years ago. You can use the car to tell you what the viscosity should be- as outlined before.

Further, todays oils exceed specifications from older oils and are fully backwards compatible.

As always, I feel that all oils used should be 0W-watever you need.

aehaas