I’ve been running Castrol 20-50 in my 20B to this point (about 25 hours).  Now that it is about ‘broken in’, I’m considering changing to synthetic.  Everyone has their favorite oil, but I’m thinking the Idemitsu racing oil; “specifically engineered to meet the unique requirements of a rotary engine”. http://www.idemitsu-usa.com/page_211.htm, would make sense.

 

It comes in 10-30 and 20-50.  Considering typical operation at high power, about 5000 rpm, and at temps of 180 -210; I’m thinking stay with 20-50.

 

Comments?

 

Al

If you run the stock OMP and feed crank case oil as the lubricant I would avoid both racing oils and multi grade oils. The long chain polymers of the multi grade tend to gum and don't burn well. The racing oils are also very stable at high temps and don't burn well, plus less detergent action would require more frequent oil changes and much greater expense.

 

The small number in a multi grade is the actual weight of the base oil. The big number is the weight it "acts"  like at operating temperature.

 

The 100% duty cycle is not hard at all on oil. Not as bad as street driving with no water boil off. Like buying a high mileage car with only highway miles on it.

 

If you premix the top oil or use Mr. Sohn's wonderful OMP adaptor to feed in a clean burning 2 cycle top oil, you can then use an automotive straight weight synthetic in the crankcase.

The automotive oil will have detergents and anti acid additives generally not used in racing oils.

 

The weight number in the straight weight is the weight of all of the oil in the bottle all of the time.

 

When you shut down and the engine cools, the gas volume change pulls in some humid air and then condenses the water out of it to manufacture sulfuric acid from the sulfer compounds in the crankcase (blow by) gasses. I run the synthetic racing oil for two weekends because I'm cheap, but its 8 quarts to the recycler and real pricy.  

 

They may have developed a way to do the viscosity increase without polymers but I doubt it.

And they do have automotive style oils if you just want to use that brand.

 

I use straight 30 weight Redline racing synthetic in the crankcase (drysump). And Redline 2 cycle synthetic in a premix. I have not installed a new main or rotor bearing in years. Side seals will go through two rebuilds. The apex seals (soft carbon) show little wear. The irons have never been resurfaced and look new.

 

I have also used straight 40 weight Valvoline racing oil with exactly the same result. This could suggest that oil choice is not critical so long as oil changes are kept up. The Valvoline was used with the stock OMP and carbon buildup on the rotors was pronounced. (An RX-2 in the IMSA RS series). So there is a distinct advantage in using 2 cycle oil as a top oil.

 

Lynn E. Hanover