182L 470 eng, JPI monitor, high CHT #4

paburke

I am flying a 182 L with the 470. No turbo etc. I have the JPI engine monitor, and upgraded from 700 to 730. Uses the bayonet probes on all cylinders except for a gasket sensor on #4. I know it is supposed to read higher as it is on/mounted with the spark plug. Mike Busch recommends temps below 380 for the continental engines. In climb, all CHTs are about 370, but #4 is over 400. In cruise, 8000-9000 msl, CHTs in 330-340 except #4. I have been leaving a bit of cowl flap open to keep lower. About 50% cowl flaps gives #4 just about 380. So the question: If all bayonet sensing cylinders are good and the gasket sensor cylinder is 50-75 higher, is it OK to disregard and close the cowl flaps? spoke to JPI, they just say expect 50-100 degrees higher on the gasket probe cylinder. they don't (won't) say that is acceptable.

Scott Sherer

Stand by while I send this to our association A&P, Erich Rempert.

Scott Sherer

From our A&P Erich Rempert:

Absolutely, close the cowl flaps.

If you look at the TCDS for the engine (I have a Navion with an IO-470) it lists the max CHT with various probes, the 460 number we're all familiar with is using a bayonet probe, with a spark plug gasket probe it's 525, and with a barrel type (never seen one) is only 290! (Limits here are for IO-470-C, refer to the TCDS for your specific engine limits, see attachment)

paburke

Not familiar with TCDS abbreviation. It looks like your source is allowing a 65 degree increase for gasket fitting readings compared to bayonet style. (Even if above the red line on the JPI monitor) So I can likely go with that. Will review the TCDS document as soon as you are kind enough to advise what it is. I have the operator manual, as well as the maintanence manual for the engine.

Your comment also noted "see attachment" which I do not see. This may contain the needed info.

V/R
pb

Scott Sherer

Hello PB,
My apology. Here's the attachment that Erich is referring to. My error.

paburke

Very helpful, thank you. Can you advise the source document? I will try to find on line for reference. Just did a 50 hour oil change, cut filter for inspection (no issues) and compression test. Two cylinders just below 60, but runs smooth and uses a quart of oil every 16-20 hours. I suspect the issue is due to prior to my ownership, it flew 400 hours from 1999 thru 2019. I purchased in December and have more than 100 so far.

Scott Sherer

These came from the TCDS, or FAA Type Certificate Data Sheets. Here's a link: https://rgl.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/Frameset?OpenPage

SalemAeroClub

Reviewing this as we're planning on an 830 install on our 470R soon. Would it make sense, and be possible, to switch the gasket probe with another cylinder? I assume the gasket probe is there to allow the continued use of a bayonet for the factory based & required CHT probe, an issue we will face and a concern as we're doubtful of this probe's accuracy.

My thought is that since you now have a recorded temperature history with the current installation, by moving probe locations you can actually verify your engine's various CHT readings with different sensors and set the 730 alarm limits accordingly.