A Simple question on the Boat Buzz the other day about using 30 wt vs 40 wt oil came up. It got me thinking that there might be more to the story why Chris Craft changed the weight need in the mid 1950’s. So I did some investigat’n. And low and behold there is a reason. Mmmm, and it has to do with WAX! It all has to do with organic chemistry. Now many of you may be thinking. Oh noooo Organic Chemistry and Woody Boater… This is going to be a mess. The good news, is no one will know if the big words are spelled right.
See crude oil contains many products from volatile gases, which would be at the top of the list, through fuels like diesel, gasoline, kerosene and then lubricating oils and greases, ultimately ending up in the heaviest components like tars used for road surfaces.
Crude oil is where it all starts and the process of fractional distillation extracts all of these and many more hydrocarbons. Paraffin which also exists in this chain was added to help as a viscosity controlant. One of two negatives of paraffin is that it did not work well at higher temperatures to maintain a high viscosity, hence oil coolers. The second negative being that after a while the paraffin would drop out of suspension thus causing sludge in the oil pan and throughout the engine.
By the 1940’s there were better viscosity controlants discovered, replacing the paraffin in the oil. A 30 weight oil of later years would maintain its viscosity better than a 40 weight would have in the 1920’s or 1930’s.
There are many other additives in oils such as dispersement agents, anti- foamants, anti-oxidants in detergents. If you want to get a leg up on this subject, you can read about aromatic and aliphatic hydrocarbons.
See! it’s simple. Here is the version that readers Digest would do.
Old additives would not hold up as well as new ones. So a 40 wt oil after 10 minutes of running would be like 30 wt. Thats it. So all along 30 wt was the correct type. This is why oil coolers were used. TO keep the wt stable. Thats it!