Originally Posted By: AEHaas
This may help from a previous session of posts:
Effect of Lubricant Properties and Lubricant Degradation on Piston Ring and Cylinder Bore Wear in a Spark-Ignition Engine, Schneider et al:
Let me begin by saying that every person interested in motor oil should go to SAE.org and purchase this article. (The paper was very detailed and I have tried to simplify the results. Also, I will need to report the results in several different postings so hang on please.) This research is made more relevant by actually using V-6 engines for wear testing - 1999 GM 3.4-L 60 degree block. And the radiotracer method of wear detection has been shown to be very accurate. They go on to say that cylinder wear and ring wear are perhaps the best areas to test oil and wear for engine longevity, particularly the rings.
Loads and RPMs varied during tests and for most tests the coolant and oils were artificially kept in the normal operating range for the engine. The coolant was not allowed to rise over 203 F and the oil was kept below 248 F. The basic test oil was a fully formulated 5W-30 quality oil. Comparisons were made between SJ GF-2 and SL GF-3 oils, both mineral based and synthetic oils were tested. Mineral based SJ oils were tested with varying quantities of ZDDP. Fully identical mineral based oil additive packaged SJ oils of different viscosities were compared. Wear rates were also tested compared to oil temperature.
Wear rates were determined by measuring the radioisotopes in the oil. It was noted that the accumulation in the oil filter was minimal. This shows that metals in the oil are a good way to measure wear. (Note that with cavitation wear the metal particles would be large and caught in the filter as would the larger dirt particles.)
Results of comparing GF-2 to GF-3 lubricants:
In general, wear rates were high during the start up period (20 minutes) as previously noted (1). Then a steady state of less wear was reached at 2,000 RPM and low load. There was a big increase in wear rate when the load was at wide open throttle, WOT, at 2,000 RPM. A modest increase was noted if you kept the load at WOT and increased the RPM to 4,000.
Actual numbers:
Average wear (ug/h) for 650 RPM, low load = 50, for 2,000 RPM, low load = 79.
For 2,000 RPM at WOT = 516, for 4,000 RPM at WOT = 758.
They state that wear is independent of RPM but there is a high correlation between wear and engine load. (This seems odd at first. You double the RPM but the wear does not double as long as the load is the same. The wear rate per revolution actually decreases with RPM. The overall wear may increase but it is less per revolution.)
They state that there is little concern for ring wear under typical light load conditions. (Typical city and steady state U.S. highway conditions.) They conclude that there were no differences between the SJ GF-2 and SL GF-3 mineral based oils in wear rates. This is the null hypothesis as the major difference between these oils is the newer lower volatility and increased oxidative stabililty between these oil classes.
Part 2:
Continuing with SJ GF-2 and SL GF-3 differences they show that there is no significant differences between the oils for the initial break-in wear of top compression rings. They state that bore wear differes from ring wear in that most wear occurs during initial break-in and with start up periods. Steady state wear is very low except when changing to high load conditions. But even here bore wear is less than ring wear rates. They reiterated that start up wear was most significant but there were no differences between the oil classes.
They compared the mineral based SJ oils for wear rates by varying the ZDDP levels. There were no differences between phosphorous levels of 0.10 and 0.05. The only other level tested was zero ZDDP where wear rates doubled. Another SAE paper showed no difference in wear as long as the level was greater than 0.03 (2). They further show that there is in fact minimal bore wear differences when no ZDDP is present. (Note that doubling the wear rate is still not too bad as the rate of wear was still relatively low.) They conclude that the newer GF-4 oils will have no negative impact on ring and bore wear rates even with the reduced ZDDP levels.
(I heard information that the ZDDP levels will be 0.05 in the GF-5 Oils.)
Oil age effects were tested by measuring wear after the oil was subjected to 16,000 miles of city driving. Although the oils thickened some, TAN increased and TBN decreased, there were no differences in wear rates from fresh oil. The test oils were mineral based SJ GF-2.
Part 3:
Fully formulated Synthetic SJ 0W-30, 5W-30 and SL 0W-30 oils were compared to SJ and SL 5W-30 mineral based oils for wear. There were no differences. (This is worth repeating - there were no differences in wear rates between mineral and synthetic based oils.)
Next are the effects of viscosity and oil temperature. Only ring wear was tested as they state it was most sensitive. They compared basic SJ GF-3 mineral oils. The additive packages were the same. The only difference was the viscosity of the base oils. The following grades resulted: 0W-10, 5W-20, 5W-30, 10W-40. The HTHS for these oils were 2.17, 2.83, 3.09 and 3.76.
There was no difference in wear rates. The oils were tested at all RPMs and Loads, no difference between oil grades were noted. All the oils had increasing wear rates as the load increased but all increased at the same rate across the board.
Most interesting to me was the way they tested wear at lower, start up, oil temperatures. In a previous study (1) they start with room temperature engines and oil showing the trend of decreasing wear as the engine heated up. In the current study they actually took a hot engine and chilled the coolant and oil from that of the normal operating temperature to a coolant temperature of around 80 F and oil temperature to 70 F. As the temperatures fell the wear increased. It reached the same rate of wear as the 4,000 RPM full load WOT. This was with the load at the minimum level. The fluids were then allowed to heat back up to normal operating temperatures and the wear rates normalized (decreased).
Wear at room temperature oil was 20 times higher than wear at normal operating temperatures. This finding is what closed the article. They stated that this will be the next focus of their upcoming research.
aehaas
(1) Effect of Break-In and Operating Conditions on Piston Ring and Cylinder Bore Wear in SI (Spark-Ignition) Engines, Schneider et al:
The rate of wear is much higher within 15-20 minutes of start-up than after reaching normal operating temperature. There was a lot of data but I conclude that the initial start-up time period (first 20 minutes) result is 100 nanometers of wear whereas the steady state wear rate was only 4 nanometers per hour thereafter. (Hence we should be concerned about start-up oil thickness more than running thickness. This justifies the statement that 95 percent of engine wear occurs just after start-up.)
(2) Development of the Sequence III G Engine Oil Certification Test, Clark et al:
Engine tests were made more severe again. (Over the years the oil ratings have improved but this has always been despite the increase in testing severity. It was III ...D, E, F, and is now III G). The oil inlet temperature was decreased from 155 to 150 C. The test was 80 and is now 100 hours. There were 8 oil level adjustments allowed now there are 5. The inlet engine air temperature was raised from 27 to 35 C. The engine load was increased 25 percent.
Despite all this the current 0W-20 oils were still GF-4 compliant and showed minimal valve train wear characteristics as long as ZDP levels were higher than 0.03 percent. (The SM rated oils I have seen so far have levels of 0.08.)
so according to this the wear rates of the car on the track(mostly under wot conditions) will be same or higher as they are on the cold start up despite the oil being at or above operating temperature...
funny I did uoa after my track event and wear did not increase, I also saw many uoa's of people that track their cars as well and did not see any significant increase in wear?
