? on Semi-Synth being better than Synth

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Nov 29, 2003
Toronto, Ontario, Canada
I remember reading a 2 page (or longer) argument back in 2000 (don't ask me to find it now, I won't be able to). But I remembered just now that the argument from supposedly a chemist, was basically that, the molecules for synthetic are different sizes than the sizes for the dino molecules, and that the synthetic molecules are all a uniform size and respond uniformly. While the organic dino molecules are somewhat variably sized and respond a little differently as a result. It went on to say, that a dino-synth blend was good because you are mixing all the different sizes of molecules together and thus can create responses to heat and wear everywhere, covering all bases basically. It SEEMS to make sense, but then again people thought for 2000+ years that if you drop a brick and a coin, the brick hits the ground first. It was only 500 years ago when someone got the idea to see for himself (Galileo). So, comments?
Well, that was before my time on this board but I won't buy the molecule size thing. As long as its small enough to get between the metals like bearings, cylinder walls, etc, then it should be good enough. Also if you scan over UOA's, the synthetics have been putting up consistently better wear numbers than their dino cousins.
Originally posted by Schmoe: ....... the synthetics have been putting up consistently better wear numbers than their dino cousins.
Where did you get that from? Syn...better wear numbers? I don't think so. Many good dino's have less ppm wear metals than famous, established synthetics. If Syn's were that good, I assure you I would have Syn in my engine now. I do have Syn (Redline MT-90) in my gearbox, but that's as far as I am willing to go. For applications such as gearbox and rear diff, Syn is feasible. But for engine oils, they have a long way to go before they make me a believer.
I don't believe that any readily available oil that we can buy has 100% uniform (synthetic if you will)molecules. I think all Syns have carrier oils, so in a sense they are semi-synthetic. It's more of a legal/commercial definition rather than a scientific fact. Plus they all have additives. I would not avoid an oil sold as a "Full Synthetic" based on this argument. I don't think this is a practical "real world" argument.
What the original post is talking about is the uniformity, not size, of PAO molecules. Conventional base oils are a mixture of different parffinic and naphtenic molecules with plenty of spaces to trap and hold contaminants. Group IV base oils are known to have inferior solvency compared to dino. That is the main reason why there is no 100 percent synthetic oil for piston engine aircraft. PAO cannot scavenge and hold all of the lead in suspension. Synthetic blends in that application work great. I'm actually surprised that PAO diesel oils exist. The additives in deisel oils must be doing it. Those additives take up 15 percent or more of the total mix, so it is not really all-PAO.
Esters are Group V, and are true synthetics, and do not have the solvency problems of PAO's. I think that all synthetics have some esters in them, for miscibility at least.
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