REFLECTOR: High Oil Temps

[Scott Derrick]

I have two oil coolers in series.

One in the nose, a -12 size positech think.  I have a flap that augments 
the airflow nicely when fully open. In the summer time I leave it open, 
In the winter I normally leave it closed. I get front cabin heat of this 
in the normal way.  I have to close the flap to get cabin heat.

I have a secondary oil cooler that is a high flow auto aux cooler, under 
the rear seat.  It has two bilge fans that can be switched between blow 
and suck.  There is a slide valve that directs one end of the flow 
between the cabin or out a reverse NACA. Setting the fan to "blow", 
slide to NACA and its a aux cooler. I see 5-10 degrees difference and 
only use it when hot in a climb or on the ground. Set fan to suck, and 
slide to cabin and it recirculates the rear cabin air and really warms 
up the back seat area.

I do not think I have oil temp problems.  In the summer, mountain west, 
think Las Vegas, 100+ OAT,  I can get close to red line in the 230's on 
the departure climb and usually level off about 2-3k AGL for a couple 
minutes at reduced power, then continue climb to cruise altitude(10-12k 
ASL). Thats my hottest test. In the winter I'm closing things up so it 
will run warm enough to heat the cabin.  I can continue the departure 
climb and not level off if approach wants it, I don't exceed 
redline(245F) but I just don't like running the engine that hot if I 
have the option.

My Bonanza ran similar, and the two Cessna T210's I used to fly run even 
hotter.

Scott

-------- Original Message --------
Subject: REFLECTOR: High Oil Temps
From: Brian Michalk <michalk at awpi.com>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Date: 06/23/2013 04:42 PM

> 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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