I have done a lot more on this problem since my last message on the
subject.
1. I purchased a new temperature gauge designed for the Rotax CHT sensors,
and rigged temporary wiring to allow me to select the display of
temperature from either cylinder 2 or 3.
2. Using this setup, I obtained the following readings at a power setting
of 25" and 4400 RPM: - #2= 215F, #3=270F and #4 (which is now fitted with
the ring thermocouple under the spark plug, which is believed to read
high)=300F. Oil temperature reading was 215F.
3. I then switched the two Rotax sensors between cylinders 2 and 3 to see
if the problem lay with a sensor, and obtained the same readings on the
same cylinders as before.
4. After a long conversation with Rotax rep Glen Saunders, we came up with
the possibility that the #3 cylinder coolant flow might be blocked. So I
disconnected the hose at the water pump outlet, disconnected the hoses for
#2 and #3 at the expansion tank, and measured the flow coolant flow
throughg both cylinders. The flow was approximately equal.
5. I then reconnected the hoses and refilled the system. I then began
making some measurements that Glen requested using my IR thermometer.
Amazingly, temperatures on the ground looked much lower than I was getting
before, So I flew the airplane. Lo and behold, everything appeared normal,
or at least acceptable. I was obtaining the following readings at 30" and
5000RPM: - #2=185F, #3=225F, #4=230F, oil temp0F. Temps at reduced
power settings were lower, but not significantly.
The only explanation I can come up with for the original problem is that
there was an air bubble somewhere in the coolant system that was blocking
coolant circulation, and that bubble disappeared when I was playing with
coolant flow.
However, all's well that ends well, and I thank all of you that contributed
suggestions and advice.
Bill Stewart, N6LB (A098)
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