5W20 or 5W30 oil for 12:1 engine

[atlantis2267]

I have a 5 month old Toyota Mark X. The car engine is a 2.5L V6 with a compression ratio of 12:1 (similar engine as the Lexus IS250 i.e. 4GR-FSE).

Driving pattern: 50:50 highway:city, but very short trips (15-30mins, 10-20 miles) and low usage (~ 700 miles per month).

I would like to use Schaeffer 7000 and the only concern I'm hesitant about 5W20 is the low HTHS (2.6). Should I use 5W30 that has a higher HTHS (3.1) with 12:1 compression ratio ?

Thanks.

cST--> HTHS FlashPoint
40°C 100°C 150°C
------ ------- ----- ----------

Schaeffer__5W20 44-45 7.5-8.5 2.6 226°C
Schaeffer__5W30 47-52 10-12 3.18 231°C

 

[PRND3L]

ummmm.... what's the car spec'd for?

 

[atlantis2267]

According to the car manual, this car is spec'd for both 5W20 and 5W30 (API SL, EC/ILSAC, GF-3). There is a corresponding footnote to use 5W20 for optimal fuel efficiency.

 

[Mitch Alsup]

The 12:1 compression ratio is immaterial. As long as the juornal bearings have sufficient area, then the difference in load from 12:1 compression down to 10:1 (or so) is small. Also note, that the loads 'taken' by these bearings are supported by a hydrodynamic wedge.

The short trip usage model also indicates that the thinnest oil you can use is going to be better for your application.

 

[Bryanccfshr]

All GR engines are now approved for 5w20 use. Run it with confidence.

 

[atlantis2267]

Thanks for all the assurance on 5W20.

I had the impression the 12:1 compression ratio generates higher temperature around the piston rings. If this is true, is HTHS rating important to look at when choosing oil?

 

[Ron AKA]

quote:

---

Originally posted by atlantis2267:
Thanks for all the assurance on 5W20.

I had the impression the 12:1 compression ratio generates higher temperature around the piston rings. If this is true, is HTHS rating important to look at when choosing oil?

---

The potential issue with the lighter and lower HTHS oils is the valve train. Research has shown that lower HTHS reduces friction in the journal bearings and in the piston skirt/ring area. However friction loss goes up in the valve train. Net/Net loss is reduced and HP increase with the lower HTHS.

This will be more of an issue with older valve train designs. Roller cam followers and four valves per cylinder reduce contact pressures and stresses. These features will make the engine more suitable for the lighter oils. You may want to consider this aspect of your engine design when you make the choice. Consider as well that the difference between 5w20 and 5w30 is very slight.

This link has much more info, if you desire to get right into it.

http://www.iantaylor.org.uk/papers/IMechEFE2000.pdf

 

[Bryanccfshr]

I am under the impression that all The GR series features oil jets to the undersides of the pistons. This lowers temperatures of the pistons and the rings allowing higher compression with more advance/less octane requirements etc. The high temperature of the 12:1 compression has been controlled through good engineering.
The HTHS as stated above is not relavent with this engine design.