So now, I have two issues - a miss in the engine at certain engine speeds and hot oil temperature. For right now, I'm just going to talk about the oil temp.
My oil temps are high, even after the addition of the aluminium sump. Let's look at what I have changed since I started on this huge rebuild.
Old *** New
Carburetor *** Electronic fuel injection
Straight inlet to carb *** Snorkels to throttle body
1 Mag & LSE ignition *** 1 mag & RWS ignition
WOT 3,050 RPM *** WOT 3,150 RPM
Steel sump *** Aluminium sump
5" prop extension *** 7" prop extension
4" inlet rings *** 4" inlet rings
Plenum baffling *** Plenum baffling
Cowling with big exit *** Cowling different, but same area
Steam gauges *** Dynon FlightDeK D180
Wing out of alignment *** New wing properly faired in.
Crappy paint *** Beautiful paint
I called Harry Hinckley, up in Iowa City, and asked if he might take a look . Harry has a highly modified Swearingen SX300 and he really knows his business and he said to come on up.
It was really hot out. Just leaving the pattern at Carbondale the OAT was 84 deg. At just 1,000' the temps started coming up so I throttled back. I had to hold it down to 2,450 RPM, then even lower just to hold the oil temp down to 230! My cylinder head temps were:
#1 - 346
#2 - 383 (#2 is consistently 50 deg hotter than the rest.)
#3 - 330
#4 - 364
When I got close to Iowa City, the ambient air suddenly dropped to 74 and my temps dropped too.
Harry looked it all over and gave more compliments than I thought I deserved. He identified three things (actually four) that I should address. He said I should have exit ramps where the exhaust exits below the firewall, I should plug all the baffle leaks to force more air around the cylinders and I should add a better ramp to smooth the air exiting the cowl. (The fourth item was to fix the miss).
We shot off to the hardware store and picked up a tube of silicone and got to work. Harry magically fabricated a couple of ramps - something I had been meaning to do for several years.
After I got the plenum off, we started caulking everything. We probably closed up 5 square inches of leaks.
The whole day, there was a sense of urgency with threatening weather to the west, and Flight Service was calling for big boomers in the P.M., but they never materialized. About 4:00 I was ready to head home and see how it helped. Harry pulled out the SX and Greg Zimmerman rode shotgun to form up and see what they could see. Harry said all the control surfaces were in alignment - so that is good, one of those things that you can't really see while in flight. He also said that it was pretty.
The air above was still in the 72 deg area, o I decided I could climb to 5,500' and maybe things would be cooler there. It was fun seeing the SX300 in formation, and naturally Harry blew the doors off of me.
But was was the result? Sadly, not much of a change. I still had to throttle way back to keep the oil temps down. My cylinder head temps were:
#1 - 316
#2 - 368
#3 - 310
#4 - 343
It appears that the cylinder head temps were better, but these were recorded with an OAT of 77 deg. Not quite sure. The oil was just as bad as ever.
I think we improved the cylinder cooling. and my Delta P (differential pressure between the top of the engine and the bottom) was higher.
This is all quite discouraging. On the two hour trip home I resolved to bite the bullet and install an oil cooler, which I really didn't want to do. It will add expense, weight, and increase overall cooling drag.
When I got home, I started looking over the Dynon support forums and I saw there was some discussion, a couple of years ago, about calibrating the oil temp sensor. When I installed my new Dynon system, I meant to do this but never did.
The proper method is to immerse the sensor in boiling water and it should be pretty close to 212. Unfortunately, the sensor is at the rear of the engine, and I have to pull the whole engine to get at it.
As I was mulling all this over at 4 A.M. today,it occurred to me that I could do this without pulling the engine. I can fly and get the engine nice and hot. Once on the ground I can have someone drop a very accurate lab thermometer that I just happen to have, into the oil pan. Can even keep the engine running. I can simple compare those temperatures and see where I stand.
If I get no luck there, I have already ordered the oil cooler parts and can start on it this weekend.
4 comments:
Paul here again from brisbane. Q? does your plenum dump onto the top of the entire cylinder area or do you have ramps to guide the air more into contact with the fins? see. http://www.x-jets.com/Design_for_optimum_cooling_efficiency.pdf for more info on this.
Looks like a good read. Thanks for the link.
another point in the text "If all other conditions remained the same, ignition advance from 25 to 42 degrees caused an increase in heat transfer of 11.4 % in the test engine which resulted in higher CHT’s. Without an ignition advance system you can expect your engine to run cooler than mine. Conversely, if you have Electronic Ignition, you can benefit by turning the ignition advance OFF if the CHT’s are getting too hot in the climb."
That's interesting. I just might try that.
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