Experience! With a 30 weight oil, I have NOT been able to keep this rule in a supra when driving hard. Again, I now think the 20W-50 is way too thick on startup and I appreciate the literature. I do, however, believe that a full synthetic 0W-50 would be more suitable for a 7m than 10W-30. Most supras, actually all supras that I've come in contact with, have had suprisingly low oil pressure. Also, the oil relief to the oil cooler is 40 psi, so the engine never meets that rule over 4k RPM in stock trim.
Higher revving engines need thinner oils.
Well, the 7m is NOT a high revving engine, it is a long stroke torque engine. I'm sticking to my guns.
In all cases you need to try different weight oils and see what happens. Then choose the correct viscosity.
Again, this is what I've done.
A 30 weight oil should be thought of as having an absolute viscosity of 110 and a 50 weight oil has an absolute viscosity of 120
At operating temp, the 50 weight is only 9.1 percent thicker than a 30 weight oil. That is why the hot idle oil pressure is roughly 5 psi higher with the 20W-50, and not substantially higher as you argue. Cold start is another story.
I then started the engine to check for leaks. The multitude of mechanical engine noises that followed nearly broke my eardrums for about 10 long seconds. Then it was suddenly very quiet. You could hear a pin drop. There was certainly the most possible amount of surface oil on all the internal parts as the engine was only off for an hour. But it was not until the oil circuit primed, filled then sent flow into all the parts that any lubrication was occurring
To a 575 maranello none the less... Are you sure we can trust this guy?:icon_razz
Jdub said:
I am very much aware of how the 7M oil system works...if you had said that you opened the bearing clearances up to the high (loose) side of spec, I would more understand the need for a heavier weight oil. That would allow the oil to flow better without as much resistance than you would see with the spec in the middle or tight side. And, a heavier weight oil will significantly increase oil pressure...more than 5 psi....especially cold. Do this: take a bottle of any 50W multigrade oil and a bottle of 5W-30 oil and put it in the freezer for an hour or so. Then pour them on a 12-18" metal pan at a 30 deg angle side by side...wanna bet which one gets to the bottom of the incline 1st? That's how well the oil is going to flow in the motor. Saying that this resistance is going to keep the "bearings from getting hammered" does not reflect how an open bearing actually works. Suggested reading...specific attention to "hydrodynamic lubrication"...the regime in which a rod/main bearing operates:
http://physicsweb.org/articles/world/15/2/7
More quotes from your links
Engine bearings and the piston mostly operate in the "hydrodynamic lubrication" region, where a thick film separates the moving metal surfaces so that there is no chance of them coming into contact.
"...If you decrease the viscosity to a lighter oil, you increase flow at a loss of pressure. High flow helps to carry away more heat. High pressure helps to keep metal parts like the bearings out of contact with each other (scuffing).”
This is why I said, "I'm counting on that resistance to flow to keep the oil in the bearing." I know that my phrasing was incorrect, but I do understand this stuff, and higher pressure will help keep the bearing from getting hammered. It is not that a thicker oil is the answer for all applications, but as you said, a thin oil will freely spray from the relief hole, whilst a thicker oil will remain in the bearing cap and prevent scuffing. A better fix would be to remove the holes and run a thinner oil. We plan on doing exactly this on Heidi's engine.
Jdub said:
About oil squirters...essentially they are nozzles. Think about what kind of liquid would provide the best spray pattern...high viscosity or low viscosity? Would you rather have a spray or a stream in this application?
The viscosity difference is less than 10% at opperating temp, I doubt that the spray pattern would suffer.
Jdub said:
Concerning cam bearings...the oil is going to drain from the top of the motor. Gravity is going to make that happen...keep in mind at engine shut down the oil is hot and is going to flow regardless of grade (the same is going to happen in the rod bearings too). Would you prefer to have oil get back up to the cam bearings quickly? Or take longer due to the resistance a thicker viscosity will experience going down the small diameter channel in the center of the cam?
On cold start, it's the 20 that's the problem, not the 50. I've still yet to see numbers for 0W-50. I'd like to see the contrast from 0W-20 to 0W-50 on cold viscosity. I noticed that 5W-50 is 210 to 0W-30's 154, ~ 36% thicker at cold start. Well, make that at warm start: 40 C.
Jdub said:
One other point...any quality oil, especially a synthetic, will not cause deposits in the motor or coaking in the turbo. The weight is irrelevant....a lighter weight oil will work as well (or better) in this regard. The turbo needs both lubrication and efficient removal of heat...particularly on a turbo that's oil cooled only. Lubrication wise, the turbo is harder on an oil due to the heat produced...that's why you want it replenished as quickly as possible...again, flow through the turbo is what you want.
I won't argue with you here. However, I've shared many long winded conversations with a few local turbo rebuilders and their general agreement is that a thicker oil will help stabilize the shaft at higher speeds, over 150K rpm. I'm sure your right that it's the synthetic part of our experience and not the weight differences that explains the lack of coaking on the turbo bearings and camshaft surfaces.
Jdub said:
I'm not discounting your experience...in fact, experience and knowledge is a very powerful combination. Consider if you were using a 5W-30 with the same results what your response would be? That is my point about the ?W-50 vs. ?W-30 debate...why did you start using the oil that you do? Is it based on hearsay from long ago, and seems to work? Perhaps there are reasons for using something different...you have to dig to uncover it.
Yes there are reasons why we started using 20W50, and I didn't have to dig deep to uncover them. In fact, I only had to dig 118 pages into the owners manual that ALL supras were equipped with to find our reason.
If you have absorbed and digested the information here you should be able to pick out the proper operating oil weight for your car, be it a 30, 40, 50 or even 20 weight oil
Yes, and that is exactly what we've done. With that said, we will certainly try using a slightly thinner oil, like 0W-50 (if we can find it), but there's no way in hell that 5W-30 is making it into our supra's oil pan during the summer months. In fact, we could run 15W-40 during even the coldest oregon winters according to toyota.
Thanks for the info, it was a very good read.
-Jake
) is unnecessarily thick.
