912 CHT - which one?

Hi all,

There is a CHT probe on the #4 cylinder, and on the #2 cylinder.
Which one to pick? I guess the 4 is the hotest, but I wonder why the #2 probe is mounted anyway?

2 and 4 are both on the left side, so perhaps to get a front and back temp? You have max limits, but also minimum for TO power, right?

Since they are both on the same carb, I would have thought perhaps something on the other side would be needed too. I have all 4 on my Jabiru, and appreciate knowing where they are all running.

..and put them on different gauges, that is? (of course I guess - but I'd ask anyway..)

If you are asking me, mine all go to the EFIS and are individually displayed along with a couple EGT's.

Hi Hans,

I believe the theory for a single CHT probe on a multicylinder engine is to put it on whichever cylinder is the hottest. I think you have it right.:)

Sincerely,

Dave S
KF7 Trigear
912ULS (with CHT probe on starboard rear cylinder)

For someone who has always run with only one sender - the hot one, is there something I might have missed not having another or all four. I always found that in my installation, the engine usually ran on the cool side, to the point that I installed radiator flaps to warm it up a bit. This time I am going to a coolant temp probe only I guess the question is, what are the risks having only one in a liquid cooled engine.
Lowell

I took to heart the observation that a 4-cyl engine is really 4 engines tied together; with each one having some differences in fuel/air, and spark, and compression, and exhaust back pressure, and cooling effectiveness, etc; which could show up as differences in CHT and EGT. Mostly the differences are not big, but if you can see what they are it gives you something else to worry about.:D

If I'm not mistaken (and I certainly could be) from my 912 days, I read that you use the front cylinder for pusher mounted engine (mounted on the rear of the aircraft) and the rear cylinder for a tractor, pull type engine. The idea is that the cylinder in the rear is the one that gets the hottest.

True?

I run a sender in both locations. On the front is my "cht" sender and the rear is "coolant" temp. The coolant temp is a solo larger gauge and the cht is a combo with the exhaust temp.

I believe my senders are on opposite sides front and rear, though.