If anyone has a theory on why my O-470 exhibits this behavior, jump in and share ideas.
When I lean in cruise (based on a single probe at the junction of each collector, left and right) and the temperatures stabilize... The temp on the right side jumps over 200 degrees when I turn on the cabin heat.
I am familiar with a rise in EGT's when you shut down a single magneto... since the flame front exits further out the exhaust valve. But I am puzzled why introducing air flow through the heat muff and then on into the cabin, causes a noticeable rise. Theories?

When you pull cabin heat and reposition that diverter door, the airflow has more resistance than when its just going overboard. Thats keeps the heat around that exhaust collector from being able to disapate as quickly, creating the temperature rise.

Okay I usually get in trouble talking about something I don't know any thing about, but...here's how my Rotax EGT gauge works.

It measures the difference between a "Hot junction" (probe) and a "Cold junction" (pin termanales on the other end of the thermocouple) . The gauge is calibrated for an OAT of 75 degrees F on the cold junction...I think...so for every one degree of OAT less than 75 the gage reads one degree high and every one degree of OAT above 75 it reads one degree low.

So...my theory is your cold junction on that side is loacted where it gets warm air from the exhaust with cabin heat off and cold outside air with heat on???

Make sure there's no blockage in your muffler/exaust system. That causes strange things, just a thought... But I think jeredp has a passing answer, the airflow in the cowling is an amazing and somewhat mystical thing at times.

Not to butt into a thread, but...

I have other weird winter issues on my 0-470. When I first start up during the winter, my #5 cylinder head and egt do not give any reading (I have an older 6 cylider GEM analyzer) until I start my run up. The engine doesn't feel like it is running rough (I've had a fouled plug that got my attention). Not an issue during the summer. Any thoughts?

Odd that both EGT and CHT refuse to read until hot...
It would be much more obvious if it was just one.
One neat trick I have begun doing... and mainly to see if my pre-heat routine is working... is to use the handheld infrared thermometers from Harbor Freight. They have a laser pointer and read to a tenth of a degree.
You could warm up and before you get any readings on number 5, shut down, open the cowl and point at each cylinder. If you truly have a cold one... you will know it immediately.

flightlogic wrote:If anyone has a theory on why my O-470 exhibits this behavior, jump in and share ideas.
When I lean in cruise (based on a single probe at the junction of each collector, left and right) and the temperatures stabilize... The temp on the right side jumps over 200 degrees when I turn on the cabin heat.
I am familiar with a rise in EGT's when you shut down a single magneto... since the flame front exits further out the exhaust valve. But I am puzzled why introducing air flow through the heat muff and then on into the cabin, causes a noticeable rise. Theories?

Check your baffling. I don't know if air for cabin heat on the O-470 is pulled off a hole at the rear of your baffling on the right side or the left, but if it is pulled off the right side rear then the culprit may be a sudden drop in the upper plenum pressure on that side when air is taken from the upper baffle area of the engine to be sent through the heat muff. If you have a leaky engine baffle seal and lowered upper baffle pressure to begin with and then cabin heat draws away more, it leaves too low a push left on the top side to force the remaining air down between the fins and so increases cylinder heating on that side first. In the cowling, the air pressure builds from the rear of the baffle and backs up to the front cylinders until it meets higher pressure ram air from the cowling inlet, then as a last step it is forced downward between the fins to cool the cylinders and heads. The air is only taking the path of least resistance and there is a lot of drag surface at the cylinder fins. You can also use a black RV type silicone to seal the gaps between the inter cylinder baffles and the fins to keep air from escaping there without first contacting the fins. This was shared with me by builders at Tea, SD, the RV capital of the midwest and builders of the RV Vangaurd squadron who gave advice when I was baffled by cooling problems of the O-360 on my Tundra. It is a great EAA chapter down there with a lot of experience.

One other point referring to the post above, I doubt that the EGT will read higher than normal if the heating begins with a cylinder cooling problem. Normal EGT but rising CHT points to inadequate cylinder cooling as the culprit and not a leaning initiated issue on that side. Do mechanics concur on this? I am experimental only.