Engine Oils and their Calculated Average
Mixed Base Oil Flash Point Temperatures

Flash point is the lowest temperature at which a chemical can vaporize to form an ignitable mixture in air. The listed flash point temp of any engine oil is for the whole product which differs from just each base oil that comprises the mixture. Most oils incluse something similar to kerosene to make the product more pourable, especially with synthetics. So the kerosene lowers the flash point that is listed which is deceiving. When the oil contacts the hot cylinder wall the kerosene and possibly the group 1 oils flash off to leave the better base oils and so it is their individual flash temps that are important, not the listed one. I have made my best effort to arrive at an average flash temp of the base oils combined to give you a better idea of how truly protective each engine oil is.

Unfortunately due to many oil data sheets not giving full information many of my averaged temps are the result of educated guesses where there was missing data. For instance an oil may list 3 different base oils but the percentages of only two of them and so I would figure the missing percentage assuming the base oil total % of the product is 80%. Or when an oil says it has around 20% of a mix of two base oils then I just averaged the flash points of the two oils together and used that in the calculation. So obviously these are just ballpark figures but I think it is still useful. This is the list of most oils used that I was able to find data on by looking up their CAS #'s :

Oils CAS#, Flash Point, Carbon #'s, and Description
64742-88-7   57C    C9-12    light wt petroleum (solvent)
64742-48-9   62C    C9-11    light wt petroleum (solvent)
64742-47-8   71C    C9-15    light wt petroleum (solvent)
68037-01-4   113C                 PAO
64742-46-7   121C   C11-25   middle wt petroleum
64742-52-5   185C   C20-50   middle wt petroleum
64742-54-7   200C   C20-59   middle wt petroleum
848301-69-6 183C   C18-50   heavy wt petroleum
64742-65-0   185C   C20-50   heavy wt petroleum
64741-88-4   185C   C20-50   heavy wt petroleum
11138-60-6   238C   C60         Ester
8001-79-4    229C                   Castor

One way to choose an engine oil is to make sure its average flash point is above the NGK plug heat rating as shown on this chart. For instance if your plug is #8 then use any oil above #11 in the listing below the chart.

Oils that didn't list enough info for me to make an estimate of their flash point averages were:
Motul 510, Motul 710, Motul Scooter Expert, Amsoil Interceptor, Lucas Semi-Synthetic.