REFLECTOR: High Oil Temps

[Douglas Holub]

I've got two oil coolers plumbed in series.  One is mounted high on the 
inside of the firewall with a fan for cabin heat and ground operations, the 
other is mounted low behind the firewall serviced by a belly scoop.  There's 
a valve that bypasses the cabin oil cooler if I don't want any heat, but I 
usually leave it on and control the heat with the variable speed fan.  The 
cabin oil cooler will lower my oil temps by about 10 degrees F.

This doesn't answer your question, just FWIW.

Doug
----- Original Message ----- 
From: "Brian Michalk" <michalk at awpi.com>
To: "Velocity Aircraft Owners and Builders list" <reflector at tvbf.org>
Sent: Sunday, June 23, 2013 6:42 PM
Subject: REFLECTOR: High Oil Temps


> 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?
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