I have dynon d120 mounted with 4 cht ring thermocouples , 4 egt probes..

Always find no 3 (right forward) the hottest with both rears staying cool. It is not above the limits in pubs O-200D ...420 cruise , 525 redline. Called factory today and asked where limits obtained upper or lower plugs. They said upper. Ive been using lower so Im going upper and upgrading to Insight brand rings.

Not trying to be  to analytical but saw Vashon Ranger  in flight video at avweb and all cylinders are much closer. 

Anyone else have data to add?  using stock baffles? or improved

experimental is fun but very OCD causing

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Hi Chris,

I'm not flying yet so no real world info for you.  You didn't say what the temps were on the other cylinders?  How about oil temps too?

I have always read that the ring sensors read hotter than probes because they are essentially connected to the spark plug but if your others are within range then maybe this is not an issue.  I have the Zenith baffle kit and haven't installed it yet but I have given it a good inspection.  It seems that the area around the prop, particularly under it, is not well sealed with baffles and a lot of your cooling air may never be making it into the upper plenum and therefore not being forced between the cylinders.  recently there was this thread in the STOL forum on high oil temps in a O200A Cruzer, with some solutions offered.  I know its not specifically CHT but the temps are all related.


I'll agree with Don on ring probes vs bayonet type. On my prior build, fleet wisdom was that the ring probes generally ran 30 deg hotter than other head locations.

Another point to consider is how new is the engine (specifically, how many hours on it)?  One engine rep said to not even talk to them about temps until 25 hrs were on the engine.

Lastly, ditto to what Don says about the baffles.  What you think might be a relatively small opening in the baffles can make a BIG diff in temps. Make sure that any seams etc are sealed with the aluminum duct tape. Are you SURE that the baffle seals between the baffles & cowl are tight against the cowl?  Are they folded-in correctly? Yours is unusual in that a front cylinder is running hot - usually it's the back cyls. In fact, I've seen many engines with a ramp on a front cylinder to force air up and over the front cylinder to help even-out the temps. The fronts are right up there in the air stream and receive the max benefit of cooling air.

found much better balance in chts using the insight brand cht thermocouples!

recommend for use with dynon, tried two other brands previously

I'm having the same problem with my newly minted STOL 750. Have about 10 hours now on it and am seeing high CHT's on #3 cylinder (O-200) in the same range as yours.  I am using stock dynon ring CHT probes on the bottom plugs.  I have an oil cooler and never see oil temps greater than about 205 degrees. After reading Mike Busch's new book "Engines" I am really concerned that Continental cylinders running hotter that 400 degrees may be causing damage. My baffles are mostly stock with added "lips" in front to stop airflow into the lower deck.  I may switch the probes to upper plugs and change sensors.  Also considering putting a lip on the aft lower cowl to aid air outflow. Would welcome other suggestions.


dynon does not supply cht rings so id be curious to know your brand.

I flew a c-150 that I installed a tso'd CHT setup and noticed the hot no. 3 there, too. I think its do to several factors. 1)descending blade 2)inefficient flow in manifold past carb. 3) stagnant air under no.3

Mike may know his stuff but remember no factory O-200 has provisions for probe mount CHT, and rings do read hot compared to the slick probe mount

since changing to insight brand rings the spreads are closer and temps better with no 3 now maxing at 400, with rings topside. planning to move rngs back to lower prior to trip to Zenith flyin sept 21 (have good data then)

if engine has new OH or cylinders it will run scary hot at first mine from factory with a factory cell run was still hot for about 2 hours if I recall

I would look at your baffles...I'm not overly impressed with the stock Zenith baffles particularly the area behind the prop, you're pretty much on your own in closing that area.  Check out David Orr's baffles a few pics down in this thread...this IMO is what a good set of baffles should look like:


Hi Chris, 

my AMD built 601XLB, Continental O-200 runs cht 1,2,3,4 as 270, 278, 304, 315 with ring probes on lower plugs.

EGT  runs 1,2,3,4 run 1216, 1284, 1410, 1296

stock baffles.

both temps are in cruise.

my baffles rubber  are starting to get stiff and I will probably change them soon.


after running with the insight cht rings


results much closer , found recommended dynon ranges as set by cubcrafters, 4 EGT segments 100 degrees each

4 cht segments 83 degrees each

looks good and im gonna leave it at that, job done

once again be careful buying rings as cheapies don't work too good, I used thermocouple joining blocks at wire harness/ probe joint

Just an update engine approaching 3 years service, recently changed to fine wire plugs. Temps closer on all cylinders

only engine expenses so far.      oil changes, fine wire plugs, and Gas!


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