Cylinder Head Temp in 231

[c1tice]

I just downloaded the data from my JPI-930 for the first time after the upgrade. I got CHT high readings on many flights. I did some research here on MS and much discussion was to keep the CHT below 400. The line on Savvy was at 400. (JPI does not support Mac I learned.) My manual says max CHT is 460. My JPI is set to 460 from the installiation. I have never gotten above 460 during a flight. Why / where is the descripency? Is the fact that this is a turbo the difference? None of the discussions I reviewed really stated the engine, ie turbo vs NA.  

[Ragsf15e]

1 hour ago, c1tice said:

I just downloaded the data from my JPI-930 for the first time after the upgrade. I got CHT high readings on many flights. I did some research here on MS and much discussion was to keep the CHT below 400. The line on Savvy was at 400. (JPI does not support Mac I learned.) My manual says max CHT is 460. My JPI is set to 460 from the installiation. I have never gotten above 460 during a flight. Why / where is the descripency? Is the fact that this is a turbo the difference? None of the discussions I reviewed really stated the engine, ie turbo vs NA.  

The conventional wisdom is that running at 460 (or even near that) is going to greatly reduce the life of your cylinders.  Most people use a maximum around ~400 in climb, ~380 in cruise.    You can probably set an alert on the jpi for 400.  My K doesn’t seem to run that hot but I have the SB engine.  I don’t think yours should be that warm.  When is it hot, in climb?  If so, what’s your power setting and ff?  You will need to address something (either technique or hardware) to keep lower than the poh max…

[skykrawler]

At the IA refresher the guy from Continental said that optimal CHT temperature range is 360-380.

The fuel pressures on that engine are supposed to be checked every annual (best case).

You didn't really say what temperatures you were seeing, when during the flight, or what power settings were at the time.

 

[c1tice]

I have the GB engine. Temps are 360 on #6 to 420 on #2 at 33 MAP and 2300 RPM at 6000', and about the same temps with 30 MAP 2500 RPM at 12000'. Just curious why the POH says one thing and TCM and "convential wisdom" are different. Intuitatively cooler CHT, to a point, makes sense for less wear but we wear things out just by using them. Makes me wonder what other POH guidlines we should ignore, make up our own or just change altogether, kind of reminds me of the Bible haha. To another point the baffeling could stand to be replaced, as we have been tweaking it for the last several annuals, that would cool things down a bit.  

[jlunseth]

The redline in the POH is 460 and that is the limit that the aircraft was certified to. JPI is required to set the redline limits to what is in the POH in a JPI unit that is STCd primary. That is why the JPI has that limit and they cannot change it. As mentioned, 460 is not good. That will hurt your engine pretty fast. The conventional thinking is that CHT's should be kept at or under 380 dF for best cylinder life. That said, it can be pretty hard to keep all cylinders in a 231 under that number under all conditions. I have recently replaced my engine, but with the old engine I had one cylinder that liked 400 and all the rest were around 380 in cruise. The 400 dF cylinder was the one that had low compressions first as the engine aged. I should say that, running LOP a great deal and with 380 as the goal, the engine was a few hundred hours over TBO when I replaced it. During a high hot climb - meaning out west in the summer and a climb to the teens or higher - I would occasionally see up to 420 until I was able to level off. As we have discussed in this forum many times, you need full power full rich for such a climb and the fuel flow per the POH should be 22.5-24 GPH. From experience it is difficult to get A&Ps to set it right, they are usually on the low side, which causes high temps in those climbs. Some of us try to get the A&P to set to 25 GPH. You can always dial it down as the pilot, but once set on the ground you can't dial it above where it was set. I found that cooling was part of the problem. I had some places where the baffling did not seal to the cowling because it went around a curve and was dimpled. When the new engine was put it I had new baffling installed and all those things corrected, and it really helped with the one or two cylinders that always ran hot.

Edited February 9 by jlunseth

[Jim F]

I would make sure your baffle seal is in good shape and not leaking air past the fins.

As most above state, setting the fuel flows correctly is a must for our 231 engines.

If your CHTs are getting to 460dF you will be doing(paying) top overhauls every 300-600 hours, so rethink that part of the POH.  Crazy part on PoH is there are written when our aircraft was new, but they have zero updates on a better way to run your engine.  This is where MS can help save you and your engine.

We have learned an incredible amount over the years on proper fuel flow set up and heat control to extend cylinder life.  High heat & high pressure kills our cylinders.

Thank you, Mike Bush, and Paul Kortopates (he is here on MS) for helping get the word out.

My GB(no intercooler/no waste gate) fuel flows are set to 25.7gpm at 2700RPM, 40inMP.  I takeoff and climb at 100% power to altitude (normally 16K-17K).   That gets me a TIT of ~1425dF, and CHTs 300dF - 330dF   This max fuel flow is 1gpm higher than the TC SID97-3G calls out (24.7gpm) but is an accepted change first pushed by RAM aircraft and everyone that knows our engines.

If my CHTs in the climb are approaching 380dF on a hot day I increase air speed.  If its 110dF OAT I am climbing at ~500ft min.   My engine is at 1950hrs and two jugs were changed before I bought it(@1200hr) and I have changed one jug for a crack in the exhaust (due to a casting void).

Jim

[PeteMc]

 

 

5 hours ago, c1tice said:

I have the GB engine. Temps are 360 on #6 to 420 on #2 at 33 MAP and 2300 RPM at 6000', and about the same temps with 30 MAP 2500 RPM at 12000'

POH and even Cont. manuals for the -GB were written maybe 50 years ago.  A lot of knowledge has been gained since we've gone from a single monitoring point to the JPI or other multi cylinder monitoring.  

As for your above power settings, you didn't say what the fuel flow was, which is a major part of the equation.  And my biggest issue (-LB), which I thought was common on most of the TSIO-360s is keeping the #5 cylinder cool.  So if you're #2 is running the hottest, I'd really wonder about the baffling.  Also, do you run with the cowl flaps adjusted so they are slightly open?  It makes a huge difference getting the air to flow through rather than just build up pressure under the cowl.