CHT/EGT Probes

[eric r]

Anyone know of affordable probes to fit the Electronics International syystem?

[easyrider]

I am thinking of replacing my EGT/CHT system with the EI monitor and was also considering what probes to use.
The system I have now is Westach which uses a multicylinder switch which is very unreliable. The switch is intermittant and even switch cleaner has not fixed the variable resistence I am getting when I switch between cylinders. Bad readings are worse than no readings.
The Westach probes appear to work OK does anyone know if they are compatable with EI instruments?
Easyrider
LongEZ 93EZ

[GlennBob]

The best way to find out is to check with E.I.  !   They should be able to tell you.  Of course they'll want to sell you theirs, but you could just order the head and hook your probes up to the unit and do a test.  Get a soup can, fill 1/2 full with vegetable oil, and put your probe in and get a good quality candy thermometer from the grocery store.  Take a torch and heat up the soup can and read the thermometer.  Check what the head is reading.  Then you can either,  if it's close, make note of how much and which way,  or if it's way off,  order the probes from E. I.  They're not that much.  I think we're talking about maybe $10.00 each ?  Carefull with that hot oil though.  Easily start a fire !

Glennbob

[Bruce Hughes]

The $10 guess is FAR from the real price.   I know; I bought 8 of
them.   Don't have the catalog or sales slip available right now.  

Sorry about that.

Bruce Hughes

[rglos]

Speaking of CHT probes is there a consensus on where to put them, upper or lower. I heard that with updraft cooling the probes should go\on the tops of the cyclinders or away from the cooling air.

As I go through these forums I se people put them with the Bayonet probes on the bottom and naturally they report sometimes 100 degrss cooler. I had mine on the top under the sparkplugs and had the same switch problem as well as the wires coming apart at the hoops.

On the first issue what gives?

[eric r]

$10 won't cover the postage! E.I. full set of egt and cht would set me back over $300 easily.
As for where to put them and spark plug gasket vs probe, look at sacramento sky ranch web info for a good rundown. I think indicated temperature is as reliable as indicated airspeed. I plan to buy and purchase some temparature tapes and calibrate from there.
I was really hoping there was an elctrical engineer who knew of some low cost ideas...

[Drew]

For CHT location, I would always go with the bayonettes regardless of updraft/downdraft.  Between sparkplugs, I believe that the bottom plug will usually run hotter (big difference between top and bottom) due to the bottoms close location to the exhaust.  

Bottom line is that lycoming cooling numbers are for the bayonette location with downdraft cooling.  If you have updraft, it is possible that your bayonettes are being cooled off by the updraft flow----so you may be indicating cooler than actual---or so the thought process goes.

In my longez, I had downdraft cooling---so no problems---the temp is the temp.  With my Cozy, I have updraft----not sure what I have in temp---try to stay below 400 in a climb and stay around 360 or so in cruise---does not appear to be melting my cylinders.

[Delta Mike]

The EI probes are Type K (Chromel-Alumel).
Temperature range is -450°F to +2500°F.
The closest generic product could be found at Omega.com with the ~ following specs:

Type K
1/8 dia (or whatever)
ungrounded
sheathed/closed tip
stainless
specify length (3")

The bigger the diameter, the slower the response time.
The smaller the diameter, the lower the life expectancy in hot gas.

When you hook it up you have to make sure you connect chromel lead to chromel lead, and likewise for the alumel leads (I think no risk of damaging anything if they are reversed, just bad data - check with EI).

Regular connectors can be used for high temp applications like EGT/CHT. For low temperature ranges like inlet air or OAT, the special type K connectors are needed, which essentially are spade connecters made out of the chromel and alumel materials.

The thermocouple junction basically makes a voltage potential based on the temperature of the junction. It's like a little battery which is near zero voltage when cold, and goes up to a maximum of about 50 millivolts when its super hot. The EI instrument just reads the voltage and converts to a number using a curve fit for Type K.

For a really low cost probe (thermocouple junction), just twist and crimp (not solder) the chromel and alumel wires together. They will generate a precise voltage based on the temperature of the junction where they first come into contact.

[GlennBob]

Woops ! !   Sorry about that ! !    I was shootin' from memory which turned out to be less than reliable.  Regarding the price of the probes,  I checked my sales  slip.  I was off by a bit there mate ! !   In July of  2001 I paid $ 55.00 / each  for the probes.  So I guess I was relying on ole' unreliable . . . .my memory ! !     Hope that sets you straight.  But the oil temp test should give you a pretty close picture as to what you'll have.

Glennbob