This should help you out a bit. Syn oil is a good addition.
These are the most comprehensive and recent ones I could find. They date to March 2003 and May 2003. I will post the numbers, add a comment or two, and answer any questions you may care to pose. These tests were commisioned by Amsoil, but since they use standardized ASTM protocols, they could easily be verified, and any deception challenged. Based on my experiences with the products from all these companies, and the results of similar but less comprehensive tests posted elsewhere, these do not look doctored or suspect. But as I did not oversee them, I cannot and will not be accountable for any discrepancies, real or imagined. This was a lot of work to type, and I strived to get them right.
1. All the oils were 10w30 viscosity
2. The oils tested were:
Castrol GTX Drive Hard (mineral)
Valvoline Synpower (syn)
Mobil Drive Clean (min) - isn't this the rebadged Honda oil?
Pennzoil Purebase (min)
Quaker State (Syn)
Quaker State Peak Perf (min)
Castrol Syntec (syn)
Pennzoil Synthetic (syn)
Mobil1 SuperSyn (syn)
The following ASTM tests were run:
Thin-film Oxygen Uptake ( D-4742)
High Temp/High Shear ( D-4683)
NOACK Volatility ( D-5900)
Pout Point (D-97)
Total Base Number (D-2896)
Cold Cranking Simulator D-5293)
4-Ball Wear (D-4172)
Test 1: Thin Film Oxygen Uptake:
Measures the oxidation stability of an oil.
The induction time (break point) in minutes is measured. The test uses standard amounts of fuel dilution, soluble metals, and water to offer a real-world applicability.
Results for this test(all units in minutes):
Amsoil: >500 (no break)
Pennzoil Purebase: 242
Castrol Syntec: 221
Vavoline SynPower: 211
Mobil Drive Clean: 209
Quaker State Peak Performance: 192
Pennzoil Synthetic: 159
Quaker State Synthetic: 159
Castrol GTX Drive Hard: 132
Test 2: High Temperature/High Shear (HT/HS)
Measures a lube's performance under severe heat and shear (mechanical stress) as would be found in the journal bearings under heavy load. The units displayed are viscosity based, using the centipose unit (cP). The minimum spec for a 30w is 2.9 cP.
Results for this test (all units in cP):
Quaker State Peak Performance: 3.37
Castrol GTX Drive Hard: 3.35
Vavoline SynPower: 3.30
Mobil Drive Clean: 3.28
Pennzoil Purebase: 3.16
Quaker State Synthetic: 3.15
Pennzoil Synthetic: 3.14
Castrol Syntec: 3.13
Test 3: NOACK Volatility.
Measures the evaporative loss of lubricants in high temperature conditions. The higher the number, the thicker the lubricant will become. API SL and GF-3 specs allow for a 15% evaporation limit. In this test, obviously, lower is better. Syns almost always have an advantage due to their monomolecularity.
Results for this test (% weight loss):
Vavoline SynPower: 7.03
Castrol Syntec: 7.77
Quaker State Synthetic: 7.80
Pennzoil Synthetic: 8.15
Castrol GTX Drive Hard: 8.93
Quaker State Peak Performance: 10.63
Mobil Drive Clean: 10.83
Pennzoil Purebase: 10.93
Test 4: Pour Point
This test reveals the lowest temperature at which a lubricant will flow when cooled under test conditions. The lower, the better the product will perform in getting from the oil pan to the upper oil galleys, and in providing oil pressure quickly. Synoils generally are the best, because they are free of wax crystals, but today's mineral oils are better refined to remove wax impurities, and use advanced pour point depressant additives to help offset the synoils' intrinsically better properties.
Results for this test (all units in degrees Centigrade):
Vavoline SynPower: -46
Castrol Syntec: -43
Pennzoil Synthetic: -40
Quaker State Synthetic: -40
Pennzoil Purebase: -37
Mobil Drive Clean: -37
Castrol GTX Drive Hard: -37
Quaker State Peak Performance: -34
Test 5: Total Base Number (TBN)
TBN displays the lubricant's reserve alkalinity, and is, of course, the opposite of TAN (total acid number). A high TBN will help resist the formation of acids from sulfur and other sources. It is also a good indicator of reserve resistance to oxidation. The higher the number, the superior ability to suspend contaminants and the greater the ability to provide long-drain intervals
Results for this test (all units in mg KOH/g):
Vavoline SynPower: 11.38
Castrol Syntec: 10.39
Pennzoil Synthetic: 9.73
Quaker State Synthetic: 7.82
Castrol GTX Drive Hard: 7.74
Mobil Drive Clean: 7.71
Quaker State Peak Performance: 7.55
Pennzoil Purebase: 7.40
RR's comments: I was very impressed with all the oils, as the mineral oils have significantly improved, consistent with previous comments about how mineral oils are closing in, and that the GF-3 spec has resulted in very good performing products. Mobil1's showing is the best i have seen for that product, which usually was in the 5-6 range previously. It certainly also supports my previous comments that the 3K oil change "necessity" is out of place with current technology. Like an enema for a dead man, while it may not help to do a 3K change, it wouldn't hurt I guess.
Test 6: Cold Crank Sumulator
This one determines the apparent viscosity of the oils at low temperatures and high shear rates, simulating the dreaded cold start. It has direct applicability to engine cranking, the lower the number the better in terms of stress on the battery, starter, etc. A 10w is tested at -25degF and must show a vis <7000 cP to pass.
Results for this test (all units cP at -25degC):
Pennzoil Synthetic: 3538
Quaker State Synthetic: 4142
Vavoline SynPower: 4541
Quaker State Peak Performance: 4620
Castrol Syntec: 4783
Castrol GTX Drive Hard: 5804
Pennzoil Purebase: 5936
Mobil Drive Clean: 6448
RR Comments: If you live and drive your car in very cold climates, the advantage of the synoils is obvious. Keep in mind that the NOACK performance figures here as well, as this tests hows the performance of fresh oil - after a few thousand miles, the oils with higher volatility will likely have thickened, unless there has been high dilution from fuel, such as can occur if excessive startup idling warmups are employed.
Test 7: Four Ball Wear
This one is a good indicator of the wear protection of a lubricant, although in the real-world it is should be factored in with the TBN of the oil. Three metal balls are clamped together, and a rotating 4th one is pressed against them in sliding contact. A scar is produced, since at some point the film strength (resistance to being squeezed out) of the oil will be exceeded. The scar is then measured, and the smaller the average wear scar, the better. This test is affected by both the base stock of the oil, and its additive package.
Results for this test (all units in inches):
Castrol Syntec: 0.45
Vavoline SynPower: 0.55
Quaker State Synthetic: 0.55
Mobil Drive Clean: 0.55
Pennzoil Synthetic: 0.60
Castrol GTX Drive Hard: 0.60
Quaker State Peak Performance: 0.60
Pennzoil Purebase: 0.65
RR Comments: Amsoil and Castrol Syntec are the clear frontrunners, indicating excellent chemistry and use of anti-wear additives. Once again, the high performance of the mineral oils against the 2nd tier synoils is notable, although one cannot dismiss the superiroity of the synoils across the board.
However, it is also admirable how well many of the mass-produced mineral oils fared. If you do frequent oil changes, they are very worth considering. The gap between synoil and the hydro-isomerized GIII mineral oils has significantly narrowed, especially when the GF-3 spec was implemented.