cyl. head temps

My 0-320 had a 100rpm drop on the left mag. so I decided to time both mags. ( mistake) It ran fine but that 100rpm drop bothered me. The left mag. was 21deg. before and the right was 23deg before. I set both at 25deg before. Now when at cruise my highest cyl. temp. (3) is 30deg. higher. I'm using the porbes that go under the spark plugs and I have read they aren't as accurate and read 30 to 50deg high. I'am in Florida and the o.a.t. was around 90deg. but I think 430deg at 2350 is a little much. In the next two weeks I have to fly up to VT. (1000 miles) and I want things right. I need some thoughts from you experts out there.

Tim
2+2

Tim, The under sparkplug probes do tend to run 50 degress hotter than probes screwed into the cylinder head. I would not worry about 430 degrees indicated, that means its running about 380 and red line is 500. I have a 150hp Clipper and they run 350 to 360.

Steve Pierce

CHT

You know Tim, there's a reason a lot of us don't run CHT's and Piper didn't put them in. One is weight of course, but the other is, less things to worry about.

Thanks guys, I closed off the 2" hole in the baffle for the cabin heat behind number 3 and that helped a little. I think I will put some duct tape over the temp. guage and that will be that.

Tim
2+2

Cylinder Head Temps

The CHT on my 160hp cub is 400-425 at cruise (2400rpm) and up to 460° on climb-out. OAT is only 60°. I switched gauges from the spark plug ring to a probe; same temps. Oil temp is good at 185°. I've checked timing, baffling.
Any ideas on how to get the temps down?

Here is the link for what Lycoming has to say about cylinder head temps.
http://www.lycoming.textron.com/main.html

One thing to consider, if you have a non-electronic CHT gage like my old
Westach dual EGT-CHT, is that the gage might be 'tweaked' for the use of the washer type thermocouples. This means, as I discovered, that your CHT might be reading 45F LOW with a bayonet type probe. Also, is everyone remembering to ADD the difference between 75F and ambient (cabin) temp to your gage reading? (subtract from gage reading if cabin is below 75F) An electronic gage is highly recomended. I solved this mess by interfacing my probe and meter with an Analog Devices AD594 chip, which compensates for cabin (ambient) temperature. I then heated a tin can full of Aeroshell 100 to 400F, measured by a candy mercury thermometer and a deep fat frier thermometer,(which agreed within 10 F) to calibrate the whole system. My CHT(#4) is pushing 500F! (All this after replacing four cylinders in the last 800 hours)
I then measured the air pressure drop across the engine, which is 2.8 inches of water at 100 mph indicated, about half of typical.(and only 0.8 at 50.) Lycoming wants to see about 4 inches. Shrouding in the front oil cooler took 10-15 F off of my oil temps, but didn't help the CHT. Replacing the baffle seals didn't help much.
I'm now measuring which of the five(!) suction ports on the cowl is not
doing it's job..I'm convinced that the PA-18 has some cooling issues that we all need to deal with. More to come.....fob

More stuff

Some progress on the cooling puzzle:
Plugging all of the holes in the baffles raised my pressure from 2.8 to 3.2 in. H2O, and reduced my CHT from 485F to 465. Installing baffles (actually, ramps) in front of the front cylinders, increased pressure from 3.2 to 3.5 inches, and reduced CHT(#4) from 465F to 445F, while raising #1 CHT from 320F to 370F. Drilling 1/4 in. holes in the baffles to avoid making a hot spot on the front(exhaust valve side) of the #1 cylinder lowered the CHT of #1 from 370 to 335F, without raising the #4 temp. It appears that the airflow to the rear cylinders is getting interfered with, perhaps by the geometry of the upper cowl or the stiffener ridge on the rear of the nose bowl. More experiments to come, though it's getting difficult to maintain the same ambient temperatures, as the season progresses...
The biggest difference was flying my friend's cub, which was the same as mine, except for leakier baffle seals and a 56 inch sensenich, whereas mine is a 54 inch. The pressures were much different. And, the CHT's were lower, but I haven't yet been able to calibrate his gage. The differential pressures were lower than mine, WHEN THROTTLE WAS BACK, but 4.2 inches with cruise power. With my sensenich or with my 41 inch Borer, there was very little difference with power. So a climb prop seems to be an aggravating circumstance. Living in the high desert has to be another....

Climb props usualy do run hotter. You run higher rpm and your going slower for less air cooling the engine. Put on bigger tires etc your going even slower for less air. Your manifold pressure may be down but you still have high rpms amd slow speed generating heat.

Good electronic CHT/EGT

Can someone recommend to me a good CHT/EGT? Looks like my old crusty oil temp guage has shot craps. I'd like to replace it with an electronic one that would also measure Oil Temp/CHT/EGT/RPM/Oil Pressure/Mach#, Gs, etc. Well really, I want to consolidate as many functions into one instrument as possible. Any recommendations?

Thanks,

murph

Cyl. head temps

Murph,

Go to the thread "Electronic fuel flow",

Lots of recomendations there re JPI 700/701

Also EI instruments too
:lol: :lol: :lol:

Doug

wait til sun n fun and save a lot on a jpi. I own 2 with fuel flow and once you own it you'll wonder how anybody flys with out one.

Murph, I'm facing the same decision. Let me know what you come up with.
I just got the last check from the insurance company so I've got a few bucks, but want to spend them wisely.

I'd 2nd the recommendations for the JPI units. Don't have anything in the -12, but have used EDM-700 series units, w/ fuel flow, in P-337 and T-210 for many years. Have had a few display related problems, but JPI has gotten much better about their repair policy (read "price"). I have also flown a P337 w/ the Insight unit, it is a distant second on display & features to the JPI units, and has it's share of failures too.
Those 450F+ temps sound awful high for a non-turbo engine, even in high ambient temps. On the Mix-master, I'm stuck w/ one washer and 5 bayonet CHT probes on each engine. Moving the washer probe to the upper deck sparkplug will lower its reading by about 50F and bring it into line w/ the bayonets.
Mikey

If all you want is to monitor CHT/EGT with high sensitivity, save some money and use an analogue instrument from KS Avionics:
http://www.ksavionics.com

A digital JPI is kind of over kill for a cub. If you're going to spend that kind of money, definitely get one with a fuel flow totalizer. Or, you could just look at your sight guages...