This is a Czech study from early 2000s, using fourteen mostly A3/B3 5W-40 oils purchased in 1999.
Interestingly, they determined the base-oil composition, namely the PAO, HC, and ester content of each oil, using chromatography.
Then, they performed an oxidation test based on the standard IP 48 method. They measured the viscosity increase, micro carbon residue, and TAN.
While the results were usually consistent with the expectation that more PAO and less HC lead to slower oil oxidation or a longer oil-change interval, there were exceptions, with some PAO-based oils performing rather poorly and some HC oils performing exceptionally well.
The culprit: antioxidants. If the antioxidants are not well-matched to the base oil or they are in insufficient quantity, you have a short oil life even with the top-quality base oils like PAO.
Moral of the story: Claims of synthetic, PAO, etc., while encouraging, do not necessarily guarantee performance. You still need a good additive package with good antioxidants in generous amounts.
Composition and oxidation stability of SAE 5W-40 engine oils
J. Cerny, M. Pospisil, and G. Sebor, Department of Petroleum Technology and Petrochemistry, Institute of Chemical Technology
I. Vaclavickova and N. Vinklarkova, Koramo a.s.
Note that in this article, synthetic refers to a PAO (API Group IV) base oil and semisynthetic refers to a PAO - HC base-oil blend.
The list of the oils tested with their determined base-oil compositions:
Spoiler alert: The article codes the tested oils with letters and does not disclose which letter corresponds to which oil in their test results.
Interestingly, they determined the base-oil composition, namely the PAO, HC, and ester content of each oil, using chromatography.
Then, they performed an oxidation test based on the standard IP 48 method. They measured the viscosity increase, micro carbon residue, and TAN.
While the results were usually consistent with the expectation that more PAO and less HC lead to slower oil oxidation or a longer oil-change interval, there were exceptions, with some PAO-based oils performing rather poorly and some HC oils performing exceptionally well.
The culprit: antioxidants. If the antioxidants are not well-matched to the base oil or they are in insufficient quantity, you have a short oil life even with the top-quality base oils like PAO.
Moral of the story: Claims of synthetic, PAO, etc., while encouraging, do not necessarily guarantee performance. You still need a good additive package with good antioxidants in generous amounts.
Composition and oxidation stability of SAE 5W-40 engine oils
J. Cerny, M. Pospisil, and G. Sebor, Department of Petroleum Technology and Petrochemistry, Institute of Chemical Technology
I. Vaclavickova and N. Vinklarkova, Koramo a.s.
Note that in this article, synthetic refers to a PAO (API Group IV) base oil and semisynthetic refers to a PAO - HC base-oil blend.
The list of the oils tested with their determined base-oil compositions:
Spoiler alert: The article codes the tested oils with letters and does not disclose which letter corresponds to which oil in their test results.