CHTs - What is acceptable?

"john smith" wrote in message
...
TripFarmer wrote:
What is an acceptable CHT in cruise? How hot can one stay in extended
cruise
flight? I've got 6 new ones and want to take care of them.

I asked those questions to each of the Lycoming and Continental reps at
AirVenture a couple of weeks ago.
The answers I got were, it depends on the engine and the airframe in
which they are installed. You need a copy of the engine manual for your
airframe. A range will be given in that reference.
I was asking about Continental TSIO-360FB in a 1979 P28T and a Lycoming
I0-520K1G5 in a 1978 PA32.


I have seen this but never understood it. Why does the maximum allowable
CHT depend on the airframe?

"Stan Prevost" wrote in message ...
\ I have seen this but never understood it. Why does the maximum allowable
CHT depend on the airframe?


Not so much the airframe but where the CHT probe is located relative to the actual
head temperatures.

Stan Prevost wrote:
"john smith" wrote in message
...

TripFarmer wrote:

What is an acceptable CHT in cruise? How hot can one stay in extended

cruise

flight? I've got 6 new ones and want to take care of them.

I asked those questions to each of the Lycoming and Continental reps at
AirVenture a couple of weeks ago.
The answers I got were, it depends on the engine and the airframe in
which they are installed. You need a copy of the engine manual for your
airframe. A range will be given in that reference.
I was asking about Continental TSIO-360FB in a 1979 P28T and a Lycoming
I0-520K1G5 in a 1978 PA32.



I have seen this but never understood it. Why does the maximum allowable
CHT depend on the airframe?
Baffeling and type of cooling (upflow, downflow, gills, cowl flaps).

I just don't buy that "airframe" stuff. A cylinder head can only take
so much temperature for so long before it gives in. 400 degrees is
400 degrees no matter what airframe it's in. If I'm wrong please tell
me why.........

I've got about 15 hours on 6 new Superior Millinieums and just put in my
first quart of oil since 2TT. I have a range of temps at cruise from
320 - 380. They dropped a lot after about the first 30 - 60 minutes of
break in and seem to have stabilized since to these numbers. The hot one
will run 400-410 in a full power climb in my PA28 235.


Trip

In article , says...

TripFarmer wrote:
What is an acceptable CHT in cruise? How hot can one stay in extended cruise
flight? I've got 6 new ones and want to take care of them.

I asked those questions to each of the Lycoming and Continental reps at
AirVenture a couple of weeks ago.
The answers I got were, it depends on the engine and the airframe in
which they are installed. You need a copy of the engine manual for your
airframe. A range will be given in that reference.
I was asking about Continental TSIO-360FB in a 1979 P28T and a Lycoming
I0-520K1G5 in a 1978 PA32.

TripFarmer wrote:
I just don't buy that "airframe" stuff. A cylinder head can only take
so much temperature for so long before it gives in. 400 degrees is
400 degrees no matter what airframe it's in. If I'm wrong please tell
me why.........

I agree the temperature a cylinder can tolerate probably doesn't depend on the
airframe, but the method of measurement might. Where is the CHT probe on the
cylinder? Don't know, but maybe Piper puts the probe in one hole, and Cessna in
another.

Dave Butler wrote:

I agree the temperature a cylinder can tolerate probably doesn't depend on the
airframe, but the method of measurement might. Where is the CHT probe on the
cylinder? Don't know, but maybe Piper puts the probe in one hole, and Cessna in
another.

In a sense, you're probably right. There's a threaded hole in the cylinder head. The
probe goes there, no matter what the airframe. The only way the airframe could make a
difference is if a) they have the probe in only one cylinder and b) the
temperatures on the other cylinders are known to be significantly different.

So, if Piper puts the probe in cylinder #1 for one aircraft and cylinder #4 in
another, the allowable max temperatures are likely to be different for the two.

George Patterson
If you want to know God's opinion of money, just look at the people
he gives it to.

"G.R. Patterson III" wrote in message ...

. The only way the airframe could make a
difference is if a) they have the probe in only one cylinder and b) the
temperatures on the other cylinders are known to be significantly different.

And both of the above are the case. Unless you have an engine analyzer
the CHT is only measuring one cylinder. They usually try to put it in the
hottest cylinder (one of the back ones), but that varies based on how the
engine cooling air is designed on the airframe.

The oil temperature temps have an even greater variation.

In a sense, you're probably right. There's a threaded hole in the
cylinder head. The probe goes there, no matter what the airframe. The
only way the airframe could make a difference is if a) they have the
probe in only one cylinder and b) the temperatures on the other
cylinders are known to be significantly different.

Actually, it can make a difference even beyond that. The fine folks at
GAMI (as part of their liquid air project) completely instrumented a few
cylinders (dozens of probes each) and went flying. They found 80
degree differences from one side of some cylinders to the other side.
So even a threaded CHT probe may or may not be telling you the true
temperature of even THAT cylinder.

FWIW, GAMI theorizes that this uneven cooling air around each cylinder
may be a significant cause of the cylinder operating "out of round" and
causing significant scuffing and wear.

"TripFarmer" wrote:
I've got about 15 hours on 6 new Superior Millinieums and just
put in my first quart of oil since 2TT. I have a range of temps
at cruise from 320 - 380. They dropped a lot after about the
first 30 - 60 minutes of break in and seem to have stabilized
since to these numbers. The hot one will run 400-410 in a
full power climb in my PA28 235.

I have the same cylinders in a LYC O-360; they have 500+ hours on them. In
order to keep mine below 380 deg., I have to keep the cowl flaps wide open
in cruise in summer at 75% power. I can lean the engine in climb for better
performance, but it takes careful attention to the mixture to keep the CHTs
under 400.
--
Dan
C-172RG at BFM

I haven't leaned much so far. Only the past 5 hours have I leaned any and
not agressively at that. I will run that one cylinder at 380-390 leaned at 75%. \
65% doesn't help but maybe 10 degrees. This is the hot cylinder. The
others run from 320 - 355. Number 3 is this hot one and number 5 is next but
20-30 degrees less. I feel as long as I keep it under 400 degrees except on
take off it should be ok. I drop back to 23 squared for extended climb and
use a more shallow climb for better cooling.


Trip



In article , says...


"TripFarmer" wrote:
I've got about 15 hours on 6 new Superior Millinieums and just
put in my first quart of oil since 2TT. I have a range of temps
at cruise from 320 - 380. They dropped a lot after about the
first 30 - 60 minutes of break in and seem to have stabilized
since to these numbers. The hot one will run 400-410 in a
full power climb in my PA28 235.

I have the same cylinders in a LYC O-360; they have 500+ hours on them. In
order to keep mine below 380 deg., I have to keep the cowl flaps wide open
in cruise in summer at 75% power. I can lean the engine in climb for better
performance, but it takes careful attention to the mixture to keep the CHTs
under 400.
--
Dan
C-172RG at BFM