Thorp Air Command - T18.net

I am about to show how little I know so please go easy on me I am sensitive

I have a J.P.I Classic 100 CHT/EGT monitor in C-GABY and a Lycoming O-320 E2D (160 hp), each cylinder has a bayonet mount CHT probe and each exhaust has a EGT probe (the EGT probe on cyl #2 is tits up and needs to be replaced).

On my most recent X-C (an hour each way down low in the 29c air) I saw CHT of 426 410 415 420,at 2000 ft ASL (DA about 4000 ft). Power was set at 23" and 2300 RPM, IAS (no wheel pants on) 138 kts (146 kts TAS). I had leaned to roughness and then enriched it a bit till smooth until I saw the high CHT. I went full rich but saw no reduction in CHTs (going higher to cooler air was not an option due BIG BIG headwinds up there).

I tow gliders in a Scout and even on the HOTTEST days and highest tows (4000 AGL) have never seen CHT above 420f.

I throttled back to 21" and slowed to 125 kts but this didn't make much impact on the CHT. I know the cooler air makes a big difference but usually see 380f or so with OAT of 15c as well.

You guys in the balmy south must have experience with HOT days so I'm looking for thoughts on how to lower cruise CHT to around 350f.

Thanks in advance.

Probably need to see some pics of your baffling/engine/inlet area . I have not seen anything over 350 deg. CHT on my 0-360, usually runs about 325 . This is in the Summer in SOCAL . I have the enclosed phelum like Danny has . We can also say the probes are good ? How old are they ? If they were all put in at the same time it just may be a cowinkydink they are all going bad at the same time ? I would put in one "new probe" and see what you see regarding temp . What is your oil temp ? Bada Bing, Bada Boom !

RB

Hi Tim, does it run these temps all of the time, or was this just one of those days when It ran a little warmer than it normally runs. Rich is right about the plenum, they are like an icebox, I don't have trouble with heat, I have trouble getting the thing to warm up. Fall and winter in Calif, I have to block off my oil cooler to see temps above 140deg in the oil. In the heat of the summer,105-108 deg OAT I am lucky to see 250 deg on the cilinder heads. Has your 0320 typically ran on the warm side? Dan

oil was running 195 to 200 degrees and I have a cooler...... most of the time it runs in the high 370-380 range and the probes are all probably 15 years old

Oil temp looks OK . Around 200 + is good to cook out the moisture in the oil . Like I said I would replace one of the probes with a new one and see what happens . 15 year old probes I would be suspect ? Is it possible the control head is FUBAR ? After 15 years I replace my skivees with new drawers !

I agree with Rich Tim, 200 deg isn't going to hurt the oil at all. I would verify that the probes are ok,before I went on a witch hunt. Thorps that are baffled just fairly well usually won't have heat problems. 15 yrs is a good long while, and a good service life for the probes, If you we're to replace just one and get totally different readings this would tell the tail what do ya think......Dan

What style cowl, & pictures of your baffling would be very helpful, Tim. I move what would be considered by some as an excessive amount of air through my engine compartment, and have never seen my CHT even approach 400 deg. 350 is hot for my setup. I have Thorp-style baffling (no plenum box), that is very tight & well sealed. The temperatures you're seeing are unusual if everything else is right.

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

Tim,
I would check the baffling to make sure there are no leaks, even a small leak can cause problems. I would also check the calibration of the probes, if you have a way to get a pot of boiling water where you can dunk a probe into it and check the temp on the monitor ( 212F or 100C ).

I have the opposite problem on my aircraft, I have too much cooling typically 300F CHT with 140F oil temps.

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Bruce Finney
N18JF T-18C #262
Yelm, WA USA

Tim - see if you can borrow a temp sensor gun from someone (for lack of a better term) - I borrowed one from work to verify my oil and CHT gauge readings - I went for a spin and got the oil up to 180, landed and immediately pulled my cheek and shot the sump, the upper screen and the plugs - my plug area was 340-345 - some cooling will low power approach and landing so I figure I was 360 or so, which is what the gauge was telling me - oil temps were plus or minus 5 degrees to the gauge, which is not graduated - just arc'd and coloured with 100, 160, 220, and redline indicators.

See http://www.avweb.com/news/savvyaviator/ ... 162-1.html
Note that spark plug gasket type probes will read about 40 degrees F hotter than the bayonet type in the bottom of the cylinder. Also, with the bayonet probe, you normally don't want to see much over 400 degrees for very long, which translates to 440 degrees for spark plug gasket type probe.

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Dave M
Sacramento
ex-T-18 owner

I have a few pics of my baffles in the PICS section but can't seem to pull em up

Like I said in my first post...

I am about to show how little I know so please go easy on me I am sensitive

I tried to find the pics I uploaded (granted it was a couple years and the other forum (same but different)) to show the state of my baffles, they fit very well I think.... but referencing the first statement leaves that debatable ... so as a related segway question.....

where are those photos? Did they migrate over to the new forum or are they lost? If they need to be re-loaded can someone point this poor blind guy in the right direction cause I have searched everywhere (well everywhere but the right place I mean).

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Lee Walton
Houston, TX
N51863,N118LW
KEFD