flyrotary@lancaironline.net Mailing List Archive

Ed Anderson wrote:

Dale , the problem with oil temps in the rotary is that the oil might be able to stand considerably higher temps (particularly the synthetic oil as you point out), but the engine suffers.

At least with the older and earlier 13B blocks, overheating could and did cause damage at a temperature range far below where you would have to worry about the oil decomposing. Overheating apparently caused the seals to "chatter" against the housing as well as reportedly "shrinkage" of the aluminum rotor housings. The guidelines were a maximum of 210F after the oil cooler for the oil and 180F out of the engine block for the coolant. Now, we have found that at least with the new blocks the engines will apparently handle higher temps without adverse effects. Apparently short excursions as high as 240F on the oil and 220-230F with the coolant can be tolerated without damage - but, the feeling is that extended operations at those temps is risking damage.

The newer blocks seem to be considerably more tolerant of somewhat higher temps reportedly due to changes in the castings, but I and others have found to our dismay that exceeding that magic number (whatever it may be) you do at risk. So that is why you will see more concern with oil and coolant temps with the rotary at a lower temperature than would normally cause concern with a reciprocating engine.

Ed

Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC

Steve ... re: the above underlined.

I would say that what you have is just fine regarding your oil temp. Remember that the "delta T" between where you are running and the temperature at where it quits working is quite high. Especially if you are using synthetic oil. Molbil I keeps lubricating quite well up past 400 degrees and beyond. Thus, if you are running temps near 200 degrees you have near a 200 degree temp spread (delta T) between what the oil can take away and what it IS taking away in BTU's of heat dissipation in a stable system. That is a pretty fat safety margin, when you figure you can run 100 degrees hotter than what you are now and still have 100 degrees left before lubrication failure is imminent. Obviously, lower is better.

Water cooling now is a different story. operating coolant at temps near 200 while water boils at 212 ... gives you a delta T of just 12 degrees to play with. I know you can kick it up by anti-freeze, pressure on the system, etc. etc. but the bottom line is that you have a lot narrower delta T range to deal with, and you are always working the system a lot closer to near it's maximum potential for heat dissipation.

Just a thought,

Dale Smith

Thanks Ed, I value your insights.

I know that seal chatter was an early development problem with the wankel, but thought that Mazda had pretty much made it a thing of the past with modern materials, geometry, and springs. I did not realize that this was a temperature dependent problem, that we still had to deal with.

Also, not quite sure what you mean re: "shrinkage of the aluminum rotor housings"? It can't shrink with heat. By this do you mean that, that having exceeded some elasticity limit, the aluminum cannot return to it's original specs upon shutdown once it has been overheated? Wouldn't it thus be oversize? Please explain ... this sure sounds like an "engine killer".

Thanks,

Dale Smith