Friday, September 19, 2014
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2009 June 16 Minimize
I "fixed" my lower cowling a couple months ago by eliminating what was a very low hanging, draggy lower section.  That change immediately caused cooling problems. Previous to this change, coolant temperatures were never a problem.  After the change, coolant temps are suddenly running 220 degrees.  I was quite surprised, to say the least.  I had many theories and started shooting them down one at a time. Oh, add to the confusion, temperatures during takeoff and climb were just fine. Once leveled off, temps climbed.

Coolant hose too close to exhaust causing it to heat the coolant. I added a sheild and moved the hose a bit. No change...

About this same time, I had started doing a lot of playing around with in-flight fuselage angle of attack to find best cruise speed (using elevator trim and reflexor position). I thought perhaps I had gotten out of my "normal" and this was the reason, I convinced myself that this had to be the case because climb temps were ok. At this point, I made a four hour cross-country flight. For the entire flight and fiddled with fuselage angle of attack, mixture settings, throttle settings, timing, everything I could fiddle with. Once during this flight, temps dropped to 200 degrees and stayed there for about 15 minutes. I was elated. However; for the next hour, I could not duplicate this.

About this time Hans Teijgeler reported on an aftermarket thermostat going bad and acting very strange - surely this was my problem. Based on the lower temp for a short period of time during the above cross-country, I thought sure this was my problem. I bought and installed a brand new Subaru thermostat. No change...

I was getting annoyed at this point so I decided to completely remove the thermostat and see what happened. I ripped the guts out of an old thermostat, installed the remains, and went flying. Of course, no change...

I spent quite a few hours just staring at the plane letting the sub-concious work. During one of these periods, I happened to spot some water "trails" on the belly. A few days prior I had gotten into some rain on my way to breakfast. These water "trails" were from that flight. The interesting thing about them is that they were straight. With the old cowling, all of these types of "trails" always flowed UP, away from the belly - or at least not straight aft. This got me to thinking that perhaps the airflow on the belly with the old cowl was so stirred up, slowed down, and/or high pressure that it flowed into the radiator duct, expanded as I wanted, and hit the entire face of the radiator. Perhaps now, with the new cowling, the airflow on the belly was "good" and was not flowing thru the duct the way I needed it to.

To test this theory, I made a flow divider and installed it in the inlet duct. I'll admit, this high tech device was made out of cardboard and was duck taped in place. I made a short test flight with this divider in place and I thought positive change had occured.  I spent a couple days building a permanent flow divider inside the inlet duct. Quite confidently, I went flying with the change.  It seemed for awhile that things were better; then, slowly, the temps started climbing.  Sure enough, back up to 220 after a bit.

I then decided it was time to focus on the radiator duct outlet since I wasn't making any progress elsewhere. My favorite building medium was used again; cardboard, to extend the outlet duct further after, provide more expansion, and larger total exit area. Interesting; this has made a difference. Flew for an hour today and temps stayed at about 200 degrees. I'm hesitant to claim any success as I have had that come back and bite me in the past. I have a cross-country scheduled for tomorrow. We'll see what happens....
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