Thorp Air Command - T18.net

Guys,

I am wondering if my engine is running too cold. Let me explain. When i bought the plane the CHT was about 360F at cruise with the outside temperature about 75F. I did some changes to the baffling and the CHT came down to about 320-325F with outside temps about 75F. This winter I sealed all the holes I could find and changed the baffle tape material to really seal everything up so all the incoming air has to go through the cooling fins.

When I did my first flight this year with the outside temp about 40F the CHT was 260-265F. Last night I was out and the outside temp was 77 F and the CHT got as high as 302F in cruise and 320F on climb out. I believe my CHT is working because it indicates the correct ambient temp before I start up.

Your thoughts on this would be appreciated. Maybe I need to poke some holes in the baffles so that they are not as efficient, or maybe cut down the air inlet area? I have a Ratray cowl.

Regards,

Jim

I think your CHTs are great, Jim. IMHO, cooler is always better - within reason of course. It’s not directly like oil temperature, where you want to reach a temperature sufficient to remove water.

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John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

For my 0-360 Mama temp. (lycoming manual) sez...

CHT

400 deg. or below .
500 deg. max .
150-400 for max service life at cont. operation .

RB

I should have mentioned I have an IO-320 in my plane.

Jim

Shouldn’t matter.

_________________
John Evens
Arvada, Colorado
T-18 N71JE (sold)
Kitfox 7 SS N27JE

Like John says, if cyl temps are mid range no problems. Just make sure oil temp is 80 C plus to keep moisture out.
Tony S
ZK-VMS

Single probe or 4? Peak EGT at cruise? Most 4 cyl lycs run best lean and in the 300-350 CHT range as previously stated.

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Base: KALX
N8786
SN 929

Your temps sound okay but there is quite a spread between 77 degrees and 325 degrees. It is posiible the probe could be good at low end and way off high. If you are serious about checking it then I suggest the probe be suspended in boiling water (212 degrees) or some other medium where you can measure the temp to check it. I ran into an oil temp probe on a PT6A a while back that was good at ambient but 20 degrees off at 212. If the error scale was constant then it could have been off by 40 at 325.

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Thorp T18
O-320-B3B (160 HP)
68x74 Sterba Propeller

"The joke in aviation is, 'If you want to make a million, you'd better start with £10m.' " -Bruce Dickinson

If the temps. are correct, you can add more performance (speed or economy) start shrinking outlets of cowl.
I would think you could bring CHTs up into the 325 range with little worry & a few more knots (or MPG)