REFLECTOR: High Oil Temps

[Brian Michalk]

Today I had a very good test flight.

I've been battling high CHT and oil temps, and made the decision to 
increase my prop pitch for todays flight to bring down RPM's.  That made 
a marked difference in CHT temps, and I could fly without redlining the 
CHT's.

Now, I still have high oil temps.  My oil cooler arrangement is two oil 
coolers in the nose in parallel.  The secondary cooler has a radiator 
fan attached with a flapper valve that doubles for ground operations and 
cabin heat.  Needless to say, the fan doesn't do a very good job, and I 
think is the source of my high oil temps.
For this thought game, assume two identical oil coolers with equal oil 
flow in parallel.  This means that each cooler gets 50% of the oil.  
Now, assume no cooling air flows through one of the coolers. The result 
is that half the oil is cooled, and the other half gets returned at the 
same temperature it began.  The result is that I get 50% of the cooling 
that's available.

What I've done in the meantime is I've capped off my second cooler. I 
have not flown with this configuration, and will do so this coming 
weekend.  I really do think this will get me within the temperature 
ranges to get around to some serious flight testing.

Now, the real question:
Given two identical coolers that flow equal parts oil, and also have 
equal amounts of airflow, is it better to plumb them in series or in 
parallel for maximum heat rejection?  It seems to me that parallel is 
like having more frontal cooler area, while in series would be like 
having a thicker cooler, with the larger frontal area being the more 
efficient design.

Does anyone have any info on this?