A multi grade dino oil contains long train Polymers that link up when heated, to get the upper pour number. As in 5W30. So it isn't 30 weight oil. It is 5 weight oil. Great for easy low temp starting and rapid warm up. Plus low drag for better fuel mileage. It is practically a rule in modern engines to use the 5W30 rating for the above reasons. But it is 5 weight oil.

 

After some use those polymer chains get chopped up and stop linking together in enough numbers and the upper rating number starts to sink.

The anti acid additives get used up and sulphur mixes with condensate on cool down to form Sulphuric acid.

 

The other problem is that the polymers are not oil but a type of plastic. It turns into a gummy black snot when burned, and eventually glues the apex seals into the slots and they can no longer follow the chrome and form a seal.

 

So, racers mix clean burning ash free 2 cycle oil with the fuel. Called premixing. The apex seals get oiled and run cooler. The crank case oil stays in the sump where it belongs and all is well. Another approach is to install Richard Sohn's OMP adaptor that provide the stock OMP with 2 cycle oil from a bottle in the firewall or other convenient mounting location. The outcome is the same. The stock OMP provides the 2 cycle oil as in the stock situation. Now the crank case oil can be more specialized without regard for how well it burns.

 

Perhaps a 30 or 40 weight full synthetic racing oil in the sump. 

 

 Much higher film strength. More anti-scuff compound. More anti acid compound. Absorbs heat faster, and transfers heat faster. Has more anti foaming additives. Rotaries foam the oil inside the rotors. Note the oil pressure drop a bit after start up. Both temperature change and oil foaming cause this. Oil containing polymers foam a lot more than oil that does not.

 

Mistral could not keep the oil temps low enough to get  to Sun&Fun to show off the Piper/Mistral combination. They had an airplane, so they put in airplane oil. A multi grade 20W50. The badly foamed oil would not cool as air is an insulator. The change to a straight weight car oil fixed the problem.   

 

For a street car the crankcase oil needs to burn as cleanly as is possible. No such data is available that I know of. So for anywhere but North Dakota I would use a nice cheap name brand straight weight 30 weight oil. More than adequate lubrication for 400+ HP (the bearings are way oversized) no polymers to gum things up. Dump in 1/4 to 1/2 ounce of name brand 2 cycle oil per gallon on each fill up, even though the OMP is in operation. Might make 200,000 miles. 

 

Full synthetics do not burn at normal operating temperatures and some of that will get into the reactor and may hose your smog test. In the early days Mazda prohibited the use of synthetics. 

 

Lynn E. Hanover  

 

 

 

AM eng. start seems normal, had what sounded like good compression ( when car came to my shop eng. spun over like no plugs were installed )  will let sit outside overnight, temps have been around 34F at night, restart next AM.  So right now eng. has real oil 10w30w & two cyc. in fuel 1/2 to 1 ratio.  Lynn if you are following, I need your input about factory request for 5w20w semi-synth. oil usage, should I instruct cust. to go back to fact. recommendations,  still need to ask him what oil he has been using, car has 130,000 miles ( no air time )  ( yet )  David R. Cook  RV6A Rotary ( sun is out right now maybe get an hr. air-time this evening ).