naz,Jun 7 2007, 01:13 PM Wrote:OAC_Sparky,Jun 7 2007, 08:39 AM Wrote:Just trying to pass some advice with good intent.
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much appreciated. thanks for the advice!!
EDIT: OAC.. what are your thoughts on why my sube manual recommends 5W30 up to 40C ambient temps, and then 10W40 after that? also, if its used hard it says straight 30 or 40 10w50 20w40 or 20w50 can be used
based on what you are saying (which i believe, since you build motors for a living, i dont) the motor has to be built to run up to 20w50 or else it would seize up.
if heavier oils are recommend for the motor if its run hard, why are they recommending 5w30 in the first place? obviously the freakin thing is going to be run hard....
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Well, just to be clear, I don't do it for a living anymore; it's one of those things that have fallen by the wayside with my other endeavours in life. As my boys get older and closer to driving age (my oldest is 16 now) that's probably something I'll be revisiting.
The problem with changing oil viscosity is that although the ambient temperature can get high, the internal temperature (all things being equal) doesn't change THAT much (keep in mind, we're talking engine, not turbo). If it did, the car would overheat, right?
So apart from startup, once the temperature inside the engine reaches its operating range, the engine (if the cooling system is working properly) is somewhat moderated under normal use. So for the most part, 30 weight would be fine. Keep in mind that as long as oil pressure is maintained that the oil film will maintain intact. It's not as though the oil will uncontrollably run away from the bearing face.
Understand that when an engine runs, that the oil pump pressurizes the oil galleries, and that oil emerges through the journal bearing face that the tolerance allows the proper formation of an oil film.
Forgive the crudeness:
Now also keep in mind that the variance is exaggerated for clarity.
What happens when the oil gets thicker, the spot where the oil enters gets thicker, but the spot on the opposite side in effect gets thinner -- when it gets to the point that it gets too thin the crank/rod stops riding on an oil film and starts riding the bearing. Then it fails. What we used to do to help avoid this was cross-drill the crank so that you in effect form two oil pockets 180* apart rather than form an eccentric oil pattern.
So, when we wanted to run thicker oil, we would purposely build the engine with a looser tolerance, because, yes, a thicker oil film is preferable to a thin one because it gives you more leeway in a performance application.
So, if your Sube manual calls for thicker oils, then obviously, the engine was built with that tolerance in mind.
I cannot say what Sube's manufacturing process is compared to Ford. But to give you a glimpse of the changes just at Ford, back in the late 80s, bare cast iron blocks were machined, the bores were measured using an air guage, then each bore was sorted into a "group tolerance" of 6-8 grades, then the proper piston size was selected based on that grade. Nowadays, the technique is much tighter: Machined sleeves are pressed into aluminum blocks, the measurement and fitting is all done electronically. Think DOS vs Windows XP. Big difference.