EDM Sparkplug Gaskets - High Temps

[Cmead]

The Varieze just returned to flight this morning!  With the temperature around 70'F we took off, wide eyed and excited...for about 10 minutes per hop, got two total in.

We put an EDM-830 in ,and at the suggestion of another, we used the spark plug gaskets instead of the CHT Head Probes.  We are reading about 420 (ish) on number 4 cylinder, (O-235-C2C - Silver Bullte Prop, 3" extension).  We can only run about 2250 RPM, in slight climb or even level flight we get those temps.  I know we have some baffle work to do, but I was wondering with the inaccuracy of the gaskets, should we be overly concerned?  Anyone else running something simular? 

EDM states that the spark plug gaskets on Lycoming "could read 50 to 60 degrees higher"!  WOW...that's totally insane when you spend good money for good information.  Are the CHT Probes really that much better?

[Marc Zeitlin]

1 hour ago, Cmead said:

EDM states that the spark plug gaskets on Lycoming "could read 50 to 60 degrees higher"!  WOW...that's totally insane when you spend good money for good information.  Are the CHT Probes really that much better?

While there is very little evidence that there is a large difference, especially on updraft cooled engines, between plug gasket probes on the top and head probes on the bottom, the answer is yes - probes in the head (if there ARE places for them - some heads are not drilled/tapped) are better and will be more accurate, because you're actually measuring what you care about and what the POH / engine operating manual determines the limits are. No one ever lists limits for spark plug gasket probes, so who knows what the right answer is? Maybe you're reading high - maybe you're reading low. No way to know.

I NEVER recommend plug gasket probes unless the heads aren't prepped for the internal probe. And I definitely recommend using probes with bayonet mounts - WAY easier to install and remove for service.

[Kent Ashton]

3 hours ago, Cmead said:

We can only run about 2250 RPM, in slight climb or even level flight we get those temps.  I know we have some baffle work to do

Some pics of your baffles would tell a lot.  Easy to post pics in these threads if you can get them from your phone to a computer.  

It's easy to make the bayonet CHT probes.  If your thermocouple wires are long enough, you can cut off the ends and make the bayonets but the type J wire is common enough.  See some here:  https://www.canardzone.com/forums/topic/18661-kents-long-ez-project/?do=findComment&comment=63649    I see the wire on ebay https://www.ebay.com/itm/Glass-Insulated-Thermocouple-Wire-GG-J-20-25-N-High-Temp-20-AWG-Type-J/253706994421?

Or you can order it from Omega   https://www.omega.com/en-us/search/?text=GG-J-20

Edited June 26, 2019 by Kent Ashton

[Cmead]

I'll try and get some pics tonight.  

Thanks for your help.

[Cmead]

I thought I would pass on an update. 

While we were waiting for the new bayonet probes to arrive, we replaced some of the old worn out black baffling material with new red/orange silicon based material and filled some of the holes with RTV.  We saw a little drop of about 20 degrees, but we know we have more work to do getting the existing baffles more "air tight". 

We wanted to switch from the spark plug gaskets to CHT bayonet probes with the no other changes, so we could compare the two, so we stopped and waited on them to arrive.  Got them installed, flew this morning.  OAT was around 80, pretty windy day but it's KS.  Temps are now running around 344 @ 2300 RPM and peaked on takeoff power around 385.  Our oil temp is getting a little high, but the heads are fairly fresh, so that could be causing some of that.

[Kent Ashton]

1 hour ago, Cmead said:

Temps are now running around 344 @ 2300 RPM and peaked on takeoff power around 385.  Our oil temp is getting a little high, but the heads are fairly fresh, so that could be causing some of that.

To use a little Apollo 11 terminology, those sound pretty nominal.  :-)  If you ever have any doubts, immerse a probe in a tin-can with an inch or two of motor oil and heat with a propane torch.  Measure with a candy thermometer.  Oh, yeah, and take a pair of Vise-grips to hold the can.