Two points:
1. It's not clear why you are using the term "flow rate"; the lubricant characteristic is "kinematic viscosity". The unit of measure is the Stoke; for typical engine oils, centistokes (Cs) is a more useful unit. "Flow rate" relative to an engine's lubrication system is based on oil pump volumetric delivery, the pressure drop (resistance to flow) through the engine's oil galleries and across plain (rod and main) bearings, and the kinematic viscosity of the lubricant.
2. Can your provide any information from any source that would support your assertion that 5W-40 is "too thick" for use in a 1GR-FE engine at normal operating temperature?
FJtest,
I agree with your first point above. Thats why I explained in my
#13 post, page 2, what kinematic viscosity is and I used "flow rate" as just a good visual. Yes the proper terminology is centiStokes (cSt), but most people including myself wouldnt recognize a centiStoke if we stepped on one.....For purposes of our discussion here i think "flow rate" gets the point across, IMO.
Your second sentence is somewhat confusing to me in that oil pump "volumetric delivery" is a whole separate issue/discussion for another day. I have been assuming that the oil pumps
in our FJ's are working as intended and designed by Toyota across the full range of RPM's. Heres why: when engine manufacturers design and build these engines, they dont build the oil pump first. Once the engine is built and the bugs worked out and the dyno tests are completed, its the engine itself that dictates what the oil demands are. The oil demands including the kinematic viscosity at operating temps, are then determined to keep the bearings and their metal counterparts with film of oil between them. So it is the engine configuration when all is said and done that dictates the grade oil necessary to properly lube the engine. Now are there issues that co-exist at the time of designing new engines ie, gas mileage, longevity, horse power, torque etc., of course. And are we splitting hairs in our discussion of oil grades, probably. But, if it wasnt important there wouldnt be all the different grades of oil.
As to your second point, there is no one source that states that 5w-40 is "too thick" for our Fj's. That is MY OPINION (FWIW) after much reading about oil in general and synthetics in particular.
Heres my thoughts on the issue. The early Fj's til 2010 called for 5w-30 (cSt of 10.4 at operating temp) oil in the owners manual. When CAFE came into play and the mandates for higher gas mileage in cars, Toyota with
their new engine, recommended a 0w-20 "gas saving" blend be used (8.7 cSt). Even the 0w-20 oil bottle says it on front. I have not read anywhere that the oil change recomendation from 5w-30 to 0w-20 was done for any reason OTHER than gas savings. And to a VERY small extent, it does that. But at what cost IMO does it diminish the protection the engine needs at full operating temps.
The standard "passenger car engine" from our Fj's, to the 650 HP Zo6 Corvette, call for Kinematic viscosity at operating temps to be about 10 cSt (+/-). The Corvette calls for 5w-30 Moblie 1
(standard fill from Chevy dexos 1 specs). If you look at the specs on the oil in my above post, you will see the grades of oil that fall with in the 10 cSt range are 0w-30, 5w-30, 10w-30.
So, unfortunately, I think Toyota's decision to go to a lighter oil was done for reasons OTHER than engine longevity. I know to some, thats hard to believe. Will 0w-20 hurt your engine, perhaps not during the warranty period, but it wont be a 150,000 mile engine either, IMHO........
BTW, the Dexos 1 specs (since 2011) are Chevy's required oil specs (Mostly high grade additive package) for all its engines across the spectrum. The 5w-40 for some reason which I am not aware of, does not meet these specs in either Amsoil or Moblie 1....Mobile 1 5w-40 is actually a diesel/gas blend application.
My opinions are just that; my opinions. I do not consider myself an expert on oil. I research the crap out of some things, and then draw my own conclusions. Everyone on this forum is free to use whatever oil they desire. My intent is not to start a forum argument with anybody on oil. I think one of the many reasons this forum is so great is the exchange of ideas and ways to do various things to our FJ's. It has been a tremendous help to me in the past years and I hope that if this thread can help someone, great. If not, thats okay too. :cheers: