Cylinder Head Temp

170C · Post by **170C** » Sun Oct 15, 2006 2:05 pm

My 0-300B has a cylinder head temp that is attached to the upper spark plug on #2 cylinder. I am wondering if what I am seeing on the gauge is reasonably correct or completely erroneous. I don't really know what the temp should be other than I believe 425 deg. is too high. Here is an example of what I just observed.

OAT- 58 deg F; ALT-2500; RPM-2500; Oil Temp-190; EGT-1300; Gnd Speed-121 mph (yea, I had a tail wind); CYLINDER HEAD TEMP- 200.
Is this where it should be?

jrenwick · Post by **jrenwick** » Sun Oct 15, 2006 11:57 pm

Hi Frank,

My 170 has an electronic engine monitor that knows all 6 cylinder head temperatures, and it always shows #2 being the hottest -- up to about 380 degrees in the Minnesota summer. So if your engine cools like mine, your probe is on the hottest cylinder, where you want it.

But it should be on the bottom plug, not the top, because the 170's cooling air flow is from top to bottom. The warmer side of the cylinder is the bottom, so that's where the probe should be.

My O300-powered Swift has the probe on the top plug of #2, because cooling air flow in a stock Swift is from the bottom up. That's why the Swift has that pretty "smile"!

Best Regards,

John

blueldr · Post by **blueldr** » Mon Oct 16, 2006 12:46 am

Ole Pokey,

John's giving you the straight poop. Updraft cooling---Thermocouple on top side. Downdraft cooling---thermocouple on bottom side.

I kind of wonder what they do with updraft cooling using bayonet thermocouples. I've only seen the thermocouple wells on the bottom side of cylinders so equipped. I, however, don't know of any installations using bayonet thermocouples with updraft cooling.

170C · Post by **170C** » Mon Oct 16, 2006 12:23 pm

Thanks guys. Guess the next time I do an oil change I need to change the location of my cyl temp probe.

HA · Post by HA » Mon Oct 16, 2006 6:23 pm

our shop has an Alcor CHT/EGT test set, it has an adapter to test the sparkplug-gasket CHT probes.

maybe you can find a local shop that has a tester and get yours checked, they should be able to check your gauge's accuracy with it too

Post by **GAHorn** » Wed Oct 18, 2006 7:29 am

Frank, the cyl head temp limit is 525 F at the lower spark plug. That means that your indications are just fine (providing they're not much different after you move the thermocouple.) My own typically runs 210-220C at the #2 lower plug.

170C · Post by **170C** » Wed Oct 18, 2006 12:47 pm

Thanks George and others. I wasn't sure of the proper temps and obviously the correct location for the sender. I will relocate this at the next oil change and see how the temps do.

Now, does this change of location of the cyl head temp ring need to be logged?

Seriously, I get confused regarding what "should" be logged and what isn't legally required. For example if the plugs are pulled & cleaned, is that supposed to be logged are is that considered a routine maint. item and not required to be logged? Adding brake fluid to the brake accumulator?

cessna170bdriver · Post by **cessna170bdriver** » Wed Oct 18, 2006 2:46 pm

170C wrote:Now, does this change of location of the cyl head temp ring need to be logged?

Seriously, I get confused regarding what "should" be logged and what isn't legally required. For example if the plugs are pulled & cleaned, is that supposed to be logged are is that considered a routine maint. item and not required to be logged? Adding brake fluid to the brake accumulator?

Frank,

I really don't know the legal requirements of logging "routine maintenance"; I leave that question to those that get paid to do it. However, I log oil and filter changes, spark plug and tire rotations, etc. , as it is simply evidence that the airplane is being regularly maintained.

Miles

futr_alaskaflyer · Post by **futr_alaskaflyer** » Wed Oct 18, 2006 9:20 pm

Interesting - my single CHT thermocouple is on the top too. Will have to stare at the baffling on my engine conversion to see if it is designed to cool bottom to top or vice versa.

170C · Post by **170C** » Thu Oct 19, 2006 10:36 pm

Miles, I log the same things you said you log. If I do anything I feel is questionable I ck w/my AI to see what he recommends. If I put a hand held gps in I don't log it because it isn't a permanent part of the airframe, but if it were a panel mount that obviously would need to be logged & signed off by the appropriate licensed installer.

Post by **GAHorn** » Fri Oct 20, 2006 2:10 am

All items listed in FAR 43, Appdx A is "preventive maintenance" and may be performed by the owner/pilot. In a seperate thought: ALL maintenance should be logged in the aircraft's records. Maintenance would include anything other than serviceing of consumeables such as fuel/oil. (You don't have to log a quart of oil added....although that is certainly a good idea. [I keep a log of all fuel and oil purchased in a running log referenced by date and tach. This makes it pretty easy to see the average fuel/oil burns.] But you do have to log an oil change which is preventive maintenance.)

See the MX Library subject regarding Preventive MX: http://cessna170.org/phpBB2/viewtopic.php?p=32726#32726

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