172N EGT

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1 week 1 day ago #3445 by CHRIS WHITTET
Replied by CHRIS WHITTET on topic 172N EGT
Steve

Thanks for getting back to me.

The EGT doesn't have an * and I'm not really concerned about the angle of the needle. It's the relative reading or position that should be important here, right?

My point is that it goes up to 3 "marks" when it's at full power - either take off power or in cruse. But when you pull back the power after leveling off, the EGT goes up (maybe because of the carb "Economizer circuit?") to 8-9 marks and you can't lean the engine from there. If you lean the mixture at 2,500 RPM, the EGT gauge doesn't go any higher as you lean it and if you go more than 3 "twists" of the mixture control, the engine starts sputtering. So at cruse at 2,500 RPM, the engine seems to be running to lean.

Is there a way to increase fuel flow so that at cruise power it's not running at it's hottest EGT?

Thanks,
Chris

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1 week 3 days ago #3441 by STEVE ELLS
Replied by STEVE ELLS on topic 172N EGT
Hi Chris,
The reason the needle isn't in the upper range of the gauge when you're at full power is because of a circuit built into the carburetor to add extra fuel (for engine cooling) during high power operations. Interestingly, it's called the economizer circuit.

If you have the EGT gauge I think you do, it may need calibrating. The little asterisk on the face is a mark that the needle should be when you leak to max EGT when you fly at 65% power.

You can adjust the position of the needle to line up with that asterisk by inserting a very small screwdriver in a small hole in the face of the instrument. Turning the small screw inside will re align a mechanism to get the needle where it should be.

If you find you can't make that adjustment, and you want to continue to use the EGT for leaning, you can probably find a replacement gauge on eBay or from a salvage yard such as Wentworth or Preferred Air Parts. These gauges were very commonly installed in Cessna singles in the 1970s and since many are being removed to install engine monitors, I know they are readily available and inexpensive. One part number for the 172 is C668501-0211. You don't necessarily need that exact part number since they were installed under many part numbers, but that should open up the different purchase options.

However, you can safely lean the engine for most efficient operation by slowly pulling the mixture knob aft until the engine becomes rough, then pushing the know forward slightly until the engine smooths out.

Let me know if this helps,

Steve

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2 weeks 1 day ago #3433 by CHRIS WHITTET
172N EGT was created by CHRIS WHITTET
Hi

I'm new to the forums, tried looking up "EGT" didn't get anywhere.

I have 2 issues with this plane, hoping you can help.

It has the Single-Double mag. On full power climb out, the EGT registers 3 marks up from off-the-scale on the left. After leveling out and pulling the power back to 2,500 RPM, the EGT rises to 9 marks up. Why? If I then lean it, the EGT will not rise and the engine will start coughing. So, it appears the mixture is to lean. Still in level flight, if I go back to full rich and push the throttle all the way in, the engine goes up to 2,700 RPM as expected, but the EGT goes down to 3 marks up.

2nd issue. The ailerons are stiff and not smooth when moved during preflight and it flies with a tendency of the left wing dropping. Many years ago, there was a push to get planes rigged properly and certain shops had people who were experienced at that. Do you have recommendations on shops? I'm in Milwaukee.

Thanks,
Chris

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