I was going to go into this long explanation of how a journal bearing works on automotive engines...it's a lot more complicated than it looks. But decided not to do that for fear of multiple eyes glazing over staring at the screen.
If you want to know more, Google boundary, hydrostatic, and hydrodynamic lubrication....journal bearings go through all 3 states as rpm increases from zero up, but primarily operate in the hydrodynamic region.
The number one reason bearings fail is due to contamination or (more obviously) lack of oil. Ask anyone that's had a BHG and didn't change the oil right away...I am convinced this is what causes rod knock in the majority of the motors you see on this forum. In the old days, air and oil filters were not that great and would allow dust to get into your oil. Bearing clearances were also not as tight a tolerance and the oils were not as good either. This is where the 50W and change your oil every 3000 miles came from. A heavier weight oil does a very good job of encapsulating particles suspended in it...this would reduce the wear to the bearings by keeping the particle from direct contact with the bearing surface. The larger clearances allowed the heavier weight oil to flow without producing excessive pressure due to restriction.
Fast forward to the present. Filter and oil technology has come a long way...synthetic oil will handle the heat produced much better without big reductions in viscosity; a good filter keeps most particles out of the oil. Bearing clearances are a lot tighter making oil flow through the bearing much more important to keep the proper film thickness (pressure) and to keep the bearing cool. A lighter weight oil will flow through a modern bearing much better. Take a look at what oil the various racing teams are using worldwide today on some extremely high HP motors.
Now, am I ever going to be able to prove by a study on the bearings used in Supra motors the effect of a 50W oil over time? No, I'm not...it's never going to happen. I don't have access to a statically large enough sample of engines. Any pictures I may be able to come up with could also have damage from other causes...you would have to know exactly what the owner did to determine the cause. The only way to prove anything would be to have a controlled study...there are too many variables in bearing dynamics and outside conditions that will affect the evidence. So, asking me to "show proof"
is an impossible question to answer.
Based on what I know about modern lubricants and filters:
- A true synthetic oil is best...especially for the heat a turbo motor produces. A synthetic can go 8,000 miles easy between changes w/ a filter change at 4,000 miles. But, if that bothers you, an oil/filter change at 5,000 miles will work. If you really want to know what's going on in your motor, have an oil analysis done every 5,000 miles and keep running it until the Total Base Number (TBN) drops to 2-3. An analysis will also tell you what contamination is in the oil and the wear metals present...other good reasons for changing the oil (not to mention figuring out why these are present).
- Use the best filter you can get. Particles as small as 10 microns can case wear to bearing surfaces. Like I've said many times, Wix or PureOne are the best...if you really want to keep your oil clean, get a remote dual filter head and use a Wix/PureOne in combo with a Trasko bypass filter. The ultimate is the Canton/Mecca set-up. It all depends on how much you want to spend
- Use the weight oil that will give you a 10 psi increase in pressure per 1000 rpm. On a Supra 7M (the way the oil relief valve is set-up) 40-60 psi is about optimum. I shimmed the relief valve (2 washers) on my new oil pump to provide 10-15 psi at idle and 40-50 psi at 3000 and above rpm. If the 1J motor uses the same type pump, this holds true. Typically a multi-grade 30W on a newer motor or a multi-grade 40W on a high mileage motor will provide all the pressure you need and the flow (especially at start) to keep the bearings working as designed. Keep in mind heavier weight oils produce more pressure due to restriction caused by viscosity through the bearings. It reaches a point where more pressure is not better, especially cold...this is the major reason why I don't use 50W oil.
- You can use whatever oil you want...almost any modern oil will work fine in any motor. At least look at the oil data sheets (available at company websites) so you know exactly what you're putting in your motor viscosity wise...it might surprise you. Additive packs are important as well...viscosity improvers like soluble moly are a plus for cutting down engine wear. If you're going to invest the $$$ in this car, at least know what your running in it.
