CHT Thermocouples

[Kyle Boatright]

I know of two kinds of CHT thermocouples - the ring type which attach at the
spark plug and the probe type which thread into a fitting on the cylinder.

Conventional wisdom is that the ring type will show significantly higher
temperatures than the probe type. I've seen differences reported as up to
50F between the two types.

Anyway, Lycoming (and Superior, and TCM, and everyone else) has
recommendations on minimum, maximum, and ideal CHT's. Which type of
thermocouple are engine manufacturers and experts referring to when they set
CHT guidelines?

KB

[Dan Luke]

"Kyle Boatright" wrote:

> Conventional wisdom is that the ring type will show significantly higher
> temperatures than the probe type. I've seen differences reported as up to
> 50F between the two types.

That's opposite to my experience. My JPI has one ring and three probes; the
ring always reads 40-50 deg. F. cooler in cruise.

--
Dan
C172RG at BFM

[john smith[_2_]]

In article >,
"Kyle Boatright" > wrote:

> I know of two kinds of CHT thermocouples - the ring type which attach at the
> spark plug and the probe type which thread into a fitting on the cylinder.
>
> Conventional wisdom is that the ring type will show significantly higher
> temperatures than the probe type. I've seen differences reported as up to
> 50F between the two types.

Someone has read John Deakin's recent AvWeb column. :-))

Email Deakin and ask him if they have tested the ones from different
manufacturers and ask him which were the most accurate in their test
stand runs.

[Kyle Boatright]

"Dan Luke" > wrote in message
...
>
> "Kyle Boatright" wrote:
>
>> Conventional wisdom is that the ring type will show significantly higher
>> temperatures than the probe type. I've seen differences reported as up
>> to 50F between the two types.
>
> That's opposite to my experience. My JPI has one ring and three probes;
> the ring always reads 40-50 deg. F. cooler in cruise.
>
> --
> Dan
> C172RG at BFM

Interesting, Dan. I have two different CHT systems installed - one is a 4
position unit which has ring type thermocouples on each cylinder. The other
has a single probe mounted to Cylinder 4. I did it that way because I wanted
to have the most accurate measure on the hot cylinder (#4 in my application)
over the long term, but added the ring type system to allow comparisons
between cylinders during the flight test of my RV. Since I have not found a
need (or excess funds) to free up the panel space from the 2nd CHT gauge,
I'm still flying with both gauges.

I always see higher temperatures on the ring type CHT than on the probe type
installed on the same cylinder.

KB