Two CHT, two EGT - which to monitor

[Bryan Cotton]

All,
My AlphaMFD can monitor two of each using type Ks. Should I monitor the rear two cylinders?

[mike.smith]

If I had to choose, that would be my choice, as they will typically run the hottest.

[lutorm]

Yeah, I'd agree with Mike, certainly for CHT. Although it would be interesting to have a front and back EGT since that's where the big mixture difference is. If you only have EGTs for the back two, you have no idea how pig rich the fronts are running...

[Bryan Cotton]

So I bought my exhaust used, and it had 4 EGTs before. How should I seal up the extra holes? I could weld them but it could be fun to move the probes around.

[woodmw]

Could you install 4 probes and incorporate a switch to change between front and back?

[wlarson861]

my Jabiru exhaust had the egt holes drilled and then filled with stainless steel rivets. Looks like they intended the engine could be run with out EGT's if the owner wished.

[builderflyer]

Bryan,

The extra holes in my exhaust are filled with CP-42 rivets. No noticeable leakage and then easily drilled out if I want to move the probes around, just to see what the difference is in EGT.

Art,,,,,,,,,,,,,,,,,,,Sonex taildragger #95,,,,,,,,,,,,,,,,,,Jabiru 3300 #261

[Bryan Cotton]

Could you install 4 probes and incorporate a switch to change between front and back?

The one issue I see is that the switch is unlikely to be chromel-alumel. This could introduce errors. I suppose you could argue that going from chromel to copper and back should be a net zero voltage. Has anybody done this in practice?

[peter anson]

The problem I see with only monitoring two cylinders is that it's impossible to know which cylinders are the hottest. The coolest running head on my Jab 3300 engine is the rearmost, coincidentally the one that is most often monitored on engines that only have one CHT gauge. In fact, I have a theory, totally unverified, that the reason some Jabiru engines in Australia have had valve failures is because they are monitoring CHT on the wrong head.
Why not just fit another gauge?

Peter

[Corby202]

I would recommend monitoring all 4. Aircraft Spruce sell changeover switch's.
On my 2.2 Jab, on the ground the two rear cylinders (cht) are the hottest, this changes over during flight, not by much but it does change.