Ernest Christley wrote: 

Question from the peanut gallery.  I don't plan to use a oil/water
exchanger, but aren't they counterproductive?

 The efficiency of the cooling relies on deltaT.  The best situation is
having the hottest coolant interfacing with the air, and it has always
been my understanding that the oil exits the engine hotter than the
water.  Will an oil/water exchanger reduce the overall efficiency of the
system by allowing the exit air, on average, to leave with less BTUs?

Tracy Crook answered:

Your questions get to the very heart of the issue and reveals more of the complexity.

 

I see you point about Delta T but since we are raising the coolant temp (using the oil to water heat exchanger) this does increase the efficiency of the radiator.   The water temp is still not as high as the oil was but there is a lot more surface area on the radiator than the oil cooler and this makes up for the smaller delta T as compared to the hot oil.   With oil to air, we are only getting the high delta T on 30% of the cooling system, with oil to water, we are increasing the efficiency on 100% of the system.

 

Lynn's point (below)  about having to do 30% more cooling with the radiator (with oil to water cooling) is true BUT, this is not the same as saying that we need a 30% larger radiator.  I don't know the exact number but much of the 30% increase in heat dissipation comes from the automatic efficiency increase from the higher delta T of the radiator.  This effect is very noticeable on the Renesis engine where the exhaust ports in the side housings add about 8 - 10 degrees (at high throttle) to the coolant temp above what the peripheral exhaust did.  I did not increase the radiator size to compensate for this because of the efficiency boost from higher Delta T.  The coolant temp after the radiator was only about 1.5 degrees hotter than before, not a big deal.  What WAS hotter was the under cowl temps (air after the radiator) which is the evidence that the air is indeed leaving with more BTUs.

 

The problem for the Renesis is that the high end water temp is possibly too high for oil to water coolers to be effective.  There may be a work around for this.  The oil cooling water may have to be tapped off at the heater port before it passes the exhaust ports.

 

Tracy

lehanover@aol.com wrote:
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>
> There is only air cooling. There is nothing else. If you can dump the excess heat through the water radiator,
>
> then its a great idea, and works just fine. Oil temps above 160 degrees cost power. The cooler the better.
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> You will need 1/3 more water cooling than you started with to make it work. You cannot fool Mother Nature.
>