This photo  of a partially removed turbulator strip and the previous photos may save Todd the trouble of cutting up his Mazda oil cooler.  The stock RX7 oil cooler has turbulator strips in the tubes but it is unlikely that they could bunch up within the tubes and further restrict oil flow.  The Mazda oil cooler is restrictive because of the turbulator strips and because it is double pass with a small number of tubes in parallel for each pass.  The turbulator strips are simply inserted in the tubes so heat transfer from those strips to the cooler core is inefficient.  The Fluidyne cooler, in contrast, has turbulators brazed or otherwise metallically connected to the tubes so the heat transfer to the core is better.  The Fluidyne cooler is also much less restrictive to oil flow.  

At times, oil temperatures of over 270 degrees was observed between the oil pump and the Mazda oil cooler with my 13B at flight power levels.  About half of the oil output from the pump was being returned to the oil sump, never passing through the cooler.  The oil coming out of the cooler which is what the bearings receive was on the high temperature end of the range for safe operation.  Since there was no interest in making French fries in the oil pan and seeing no point in continuously and unnecessarily pumping over 14 gal/min  of such hot oil at 150 psi, the system was modified.  Call it paranoia if you wish.  A Fluidyne oil cooler of very similar dimensions to the original Mazda cooler was installed without changing the air inlet ducting.  The result was no oil returning directly back to the sump and the necessity of blocking part of the air flow to obtain reasonably warm oil temperatures.

I am not a Fluidyne representative.  Ed once gently reminded me that I was a scientist and not an engineer, so while I collect data, I am not qualified to speculate on why the results occurred.   :)  Feel free to draw your own conclusions.

Steve Boese

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