Technical Oil pressure question related with load/heat/lapping
01-04-2004, 02:22 AM
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Technical Oil pressure question related with load/heat/lapping
When running at track events, I noticed that oil pressure will drop, not significantly, but lower to ~ 60-65psi after 5 hard laps. The starting point on the first lap will be around 75-80psi. What's with the reduction in oil pressure? I've heard a nasty rumor that a few of the spec miata guys are switching back to non-synthetic oils to keep oil pressures up, what gives?
01-04-2004, 04:43 AM
#2
Would have to guess that it is simply the heat resulting in oil at it's lowest viscosity. Most of us don't have gauges so we don't know what pressure we are running.. at what rpm are you seeing that number? The spec in the manual just shows minimums of 36 psi at idle and 85 psi at 3000 rpm.
Changing the viscosity of oil may be an option but changing away from synthetic does not make sense to me as it should have less variation from the spec.
I know that all the lubricants thin substantially with hard running, but it seems that on my car it is most extreme with hours of sustained high speed which is on the highway, not the track.
Changing the viscosity of oil may be an option but changing away from synthetic does not make sense to me as it should have less variation from the spec.
I know that all the lubricants thin substantially with hard running, but it seems that on my car it is most extreme with hours of sustained high speed which is on the highway, not the track.
01-04-2004, 05:57 AM
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We're seeing similar pressures and I would agree that it is due to oil temperature. We have seen oil temps hit ~290 and that is why we are going to an oil cooler. I am going to follow DavePK's path as his worked real well for him.
-Pete
-Pete
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01-07-2004, 04:05 PM
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Oil thinning is fairly constant with temperature increase - those claiming that their oil pressure went "right" after replacing synoil with mineral oil are not conducting a rigorous, apples to apples analysis. If anything, the lower friuction and inherent reduction in heating from synoils inherent molecular firction (that is, it resists heating itself better than mineral oils) would tend to argue the case for LESS drop in PSI at higher temps. There is variance among brands even within the 10w30 spec, and when you factor in possible thinning of used oil from fuel dilution, and the higher NOACK volatility of mineral oils, it is entirely possible that under racing conditions and high temps, the mineral oil will thicken, and raise the oil pressure, since it is almost entirely a function of temperature increase.
But thicker oil flows slower, and mineral oil absorbs and releases heat less efficiently than mineral oil, so to my mind, giving up a number of oerformance benefits to hit some magic oil pressure figure is bad logic. The S2000 spec is 85 PSI at 176degF, but the thinning goes up from there, and hence the oil pressure drops.
If you are good in math, here is some tribology:
http://www.mme.tcd.ie/~torrance/Cnotes/Tri...otes/Trib4d.pdf
But thicker oil flows slower, and mineral oil absorbs and releases heat less efficiently than mineral oil, so to my mind, giving up a number of oerformance benefits to hit some magic oil pressure figure is bad logic. The S2000 spec is 85 PSI at 176degF, but the thinning goes up from there, and hence the oil pressure drops.
If you are good in math, here is some tribology:
http://www.mme.tcd.ie/~torrance/Cnotes/Tri...otes/Trib4d.pdf