Cylinder temperatures

[dbohm]

What are normal cylinder temps on climb out? I have a 49 A model does not have seaplane lip. Have a 6 cylinder digital monitor. Sea level ops @ 85F climb out @ 85 mph number 1 and 2 cylinders are getting up around 450 degrees 3 and 4 are near 390 and 5 and 6 in the 370 range. Can anyone tell me if this sounds like expected temp range? I have got the air box about as tight as I can ( there were some areas that were letting air exit the top of the box) however it has not changed temps. Cruise temperatures are all much lower with # 1 and 2 running about 400 degrees.

[jrenwick]

Here are the O-300 specs:

O300A.pdf

CHT maximum is 525 in climb, recommended max 420 in cruise.

There can be a lot of variability in oil and cylinder head temps between various 170s, even if identical in the outward appearance of engine installation, baffling, cowling, etc.

Exhaust valves are the thing most affected by cylinder head temperatures. Check compressions annually, look for exhaust leaks, and if they're caught early, they can be reground without major expense.

The red knob (mixture) is the cylinder head temp. control.

[n2715d]

We learned the hard way that, without a CHT gauge, an oil temperature gauge serves only to indicate you’ve already damaged the engine. Our 170 cowl has the “doghouse” baffles, and we were forced to pull two low time jugs for overhaul after experiencing stuck exhaust valves. We installed a scanning CHT at our next annual. We had purchased it some time earlier but didn’t get around to installing it until we got bitten. Would have saved us time and expense had we installed it before.
We found #2 consistently exceeds 400 degrees on climb out, especially with full load. Notwithstanding the specs in the TCM pdf referenced above, numerous published articles warn against CHT above 400 degrees. https://www.aopa.org/news-and-media/all ... -hot-heads advises that operations above 460 has resulted in catastrophic failure of a TCM engines with solid valve stems.
The lesson here was the necessity of a CHT gauge. At the very least, a single sensor CHT installed on #2, consistently the hottest jug by 20 degrees. Ours seems to top out at 415 degrees on climb flying at 92 OAT. We now regularly drop the nowse above 400. The CHT cruise specs published by TCM appear to invite engine failure, if any of the more recent myriad CHT articles are accurate.

[darhymes]

I’ve been dealing with this. Sorry to hear you are dealing with it as well. I have a 1955 170B, No seaplane lip. No oil cooler. I originally had a CHT gauge on the #1 cylinder. It indicated in the vicinity of 400 on most climbs. I then had a 6-cylinder monitor installed. Turns out the #1 cylinder is one of the coolest (rarely over 370) and #2 is, by far, the hottest…easily reaching past 420 if unchecked. I tightened up the baffling (repaired and/or replaced a few pieces and installed new baffle seals) and checked for induction leaks (none). After scratching my head for some time while babying my engine, I had the timing re-checked. Turns out my two previous IAs didn’t check it properly. Timing was way off. Since then, my only “problem child” is still my #2. It will still reach for 420 if I don’t do anything about it. The rest of the cylinders prefer to operate at average temps. To keep #2 from over-temping, I manage throttle and speed (85-90mph) during climb to keep the temp below 400.

At this point, I’ve given up trying to fix anything else to reduce the #2 temps and just plan my flights to ensure there is no need for full power during en route climb. Last year I flew to Oshkosh. Had a couple days that I took off at 4am and circumnavigated as much high country as possible, which allowed me to climb at reduced power settings. Added a few hours to the round-trip time but peace of mind to not worry about pushing my engine temps. By the way, my oil temp is fine. #2 cylinder is the only issue I have. The airplane would be perfect if that cylinder didn’t bother me all the time.

I have included a couple screenshots of my engine data for your reference. The first photo highlights the highest temps during climb where ground temp was close to 100. I managed throttle well and was able to keep #2 below 400 during the climb. The next photo is an example where I did not manage the throttle/speed well. #2 temp reached 415 and then slowly rolled back to a more manageable temp. Note the OAT in each example. Also note CHT for #1 cylinder. It’s one of my coolest.

While trying to get the baffling tightened up, I noticed the PMA front baffling pieces exposed nearly the entire cylinder to airflow, resulting in very cool 5 & 6 cylinders. I also found this increased the temps of the middle and rear cylinders (did a LOT of testing!). I then copied the baffling from a ‘56 172, which blocks direct airflow to much of the front cylinders. This resulted in my front cylinders operating at normal temps and the middle and rear cylinders being a few degrees cooler overall. I hope this helps.

[darhymes]

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[GAHorn]

According to TCM X30013 Ovhl Manual the Cyl Hd Temp limit is 525. If the indicating system is accurate, 420 wouldn’t concern me during climb.

I believe that the carburetor delivers addt’l cooling-fuel mixture at full-throttle position…and why full throttle climbs are recommended.

Reducing pitch to gain greater forward speed is good for engine cooling however. Those front cyl baffles are also good.