Normal EGT - Very Low CHT

I was flying yesterday and noted on my GEM that on cyl #1, the EGT was
normal, but the CHT was very low. Most of the time the CHT was off the
scale low, so there was essentially no reading, but occasionally it would
come up enough to be at the bottom or one bar from the bottom of scale.

I can't think of a scenario which would cause normal EGT, but CHT 150 deg
lower than normal. The engine runs normally. So I'm suspecting a bad CHT
sensor although it if failed outright the GEM manual says it would just be
missing all the time. Any other ideas? (This is on an IO-520 in a Bonanza,
BTW.)

- Mark

On Wed, 03 Mar 2004 17:36:59 GMT, "markjen"
wrote:

I was flying yesterday and noted on my GEM that on cyl #1, the EGT was
normal, but the CHT was very low. Most of the time the CHT was off the
scale low, so there was essentially no reading, but occasionally it would
come up enough to be at the bottom or one bar from the bottom of scale.

I can't think of a scenario which would cause normal EGT, but CHT 150 deg
lower than normal. The engine runs normally. So I'm suspecting a bad CHT
sensor although it if failed outright the GEM manual says it would just be
missing all the time. Any other ideas? (This is on an IO-520 in a Bonanza,
BTW.)

- Mark


Loose connection.
Bad probe
Bad channel in the GEM.


Ron (EPM) (N5843Q, Mooney M20E) (CP, ASEL, ASES, IA)

You nailed it.

Jim


Ron Rosenfeld
shared these priceless pearls of wisdom:

-Loose connection.
-Bad probe
-Bad channel in the GEM.



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

"markjen" wrote:
I can't think of a scenario which would cause normal EGT, but
CHT 150 deg lower than normal. The engine runs normally.

I'm betting on Ron's #1 choice: a bad connection. First place to look
is the splice between the wire coming from the GEM and the lead coming
from the probe. These are often screw/star washer/ring terminal/nut
affairs that can become loose. They're usually in the engine compartment
covered by sleeves.
--
Dan
C172RG at BFM
(remove pants to reply by email)

When my mechanic had my JPI installation half finished, I noticed in the
installation manual that JPI specified the star washer be _between_ the ring
terminal from the probe and the wire to the display. I thought that was
interesting and unusual. He had been putting them under the nut. After I
pointed that out, he made the remaining connections with the star washer
between the terminals. I've noticed no difference in operation so far.

Jon

"Dan Luke" wrote in message
...
"markjen" wrote:
I can't think of a scenario which would cause normal EGT, but
CHT 150 deg lower than normal. The engine runs normally.

I'm betting on Ron's #1 choice: a bad connection. First place to look
is the splice between the wire coming from the GEM and the lead coming
from the probe. These are often screw/star washer/ring terminal/nut
affairs that can become loose. They're usually in the engine compartment
covered by sleeves.
--
Dan
C172RG at BFM
(remove pants to reply by email)

Thanks for all the good ideas guys, appreciate it.

- Mark

On 3-Mar-2004, "markjen" wrote:

I can't think of a scenario which would cause normal EGT, but CHT 150 deg
lower than normal. The engine runs normally. So I'm suspecting a bad CHT
sensor although it if failed outright the GEM manual says it would just be
missing all the time. Any other ideas?


Is it possible that the probe is not making good thermal contact with the
cyl. head?

--
-Elliott Drucker

"Jon Woellhaf" wrote:
... I noticed in the installation manual that JPI specified the star
washer be _between_ the ring terminal from the probe and
the wire to the display.

I've had one become loose, but I don't remember what the assembly order
was. Next time I've got the cowl off, I'll check a couple.

Thanks for the tip.
--
Dan
C172RG at BFM
(remove pants to reply by email)