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PA28 CHTs during climb

Recently installed four new jugs on my O-360-A4M and also a CHT gauge. The CHT gauge is cold junction compensated, and the thermocouple sensor is installed in the CHT well of cylinder #3 (rear right side).

What temperature would I expect to see during climb out at Vy (85mph/76kts) a standard like day? It will easily pass 400 unless I go for a higher airspeed or reduce throttle a bit. The latter has most effect.

The baffling looks quite all right, but there are some minor joints etc which can be sealed with sealant.

(My oil temp on Aeroshell Oil 80 (straight mineral) is 180F on the original oil temp gauge.)

Regards

It will easily pass 400 unless I go for a higher airspeed or reduce throttle a bit.

Really? Full rich? In that case you may want to check your fuel flow.

My guess is that you should not see anything higher than 340-350.

Last Edited by at 15 Sep 18:10
LFPT, LFPN

GaryStorm wrote:

the thermocouple sensor is installed in the CHT well of cylinder #3 (rear right side)

One CHT sensor only will not show you much. You have no idea how #3 compares to the others. It’s not always the same cylinder that is hottest.

GaryStorm wrote:

What temperature would I expect to see during climb out at Vy (85mph/76kts) a standard like day? It will easily pass 400 unless I go for a higher airspeed or reduce throttle a bit.

You can’t climb at Vx/Vy without frying your engine. It’s normal to see > 400°F when doing that and the solution is to make sure your baffling is in perfect shape and also do not climb out at Vy (you wouldn’t use Vx anyway after clearing obstacles). For a Lycoming, a good rule of thumb is to stay below 380°F and never ever exceed 400°F. Climbing is basically a CHT exercise.

Aviathor wrote:

Really? Full rich? In that case you may want to check your fuel flow.

You can’t really adjust anything in a carbureted engine.

Last Edited by achimha at 15 Sep 18:18

You can’t really adjust anything in a carbureted engine.

You can adjust the mixture on the carb, can’t you?

LFPT, LFPN

Yes, it is carburated and this is full rich on the mixture.

There is a basic adjustment on the carb, which I presume is correct, as there is plenty of cooling effect on EGT on going full rich. Someone mentioned full-rich EGT should be at least 50-100 rich of best power (EGT), I have not looked into this yet. Perhaps someone can enlighten me?

Of course one probe does not give any information on the other three cylinders, however it does give information on #3. One CHT probe is far from an engine analyzer, but it is helpful in educating and disciplining the pilots (club wet lease). Besides, the other three wells has Tanis heaters in them.

Thanks for the advice so far,
Gary

Check your baffles !

FAA A&P/IA
LFPN

Show us a picture of the baffles!

spirit49
LOIH

Someone mentioned full-rich EGT should be at least 50-100 rich of best power (EGT), I have not looked into this yet. Perhaps someone can enlighten me?

Have a quick read here

Full-rich is a lot richer than 50-150F ROP. It is about 150F ROP.

Baffles and baffle seals are important. Do a search on EuroGA for “baffle” etc. A 5mm gap through which air can escape can raise the CHT by maybe 30F. I re-did my seals a few years ago, using two different materials. The PTFE-coated one at the top and the floppy one from Browns along the sides. The CHTs dropped by about 40F.

Administrator
Shoreham EGKA, United Kingdom

achimha wrote:

You can’t climb at Vx/Vy without frying your engine. It’s normal to see > 400°F when doing that and the solution is to make sure your baffling is in perfect shape and also do not climb out at Vy (you wouldn’t use Vx anyway after clearing obstacles). For a Lycoming, a good rule of thumb is to stay below 380°F and never ever exceed 400°F. Climbing is basically a CHT exercise.

I don’t think you can make a blanket statement like that. It depends a lot on the engine and aircraft. With our C172S with a 180 hp Lycoming I certainly don’t exceed 400°F CHT on a Vy climb – and I don’t even run full rich but leaned to max. rpm according to the POH. I haven’t had reason to try Vx.

Obviously the higher the engine power, the greater the cooling problem.

Last Edited by Airborne_Again at 16 Sep 07:57
ESKC (Uppsala/Sundbro), Sweden

Airborne_Again wrote:

I don’t think you can make a blanket statement like that. It depends a lot on the engine and aircraft. With our C172S with a 180 hp Lycoming I certainly don’t exceed 400°F CHT on a Vy climb

Yes, there are a few aircraft that are not designed for touring and have huge air intakes. The C150 and C172 come to mind. The C182 is already aerodynamically optimized for which the air intake is one of the biggest areas in aircraft design. The PA28 has a much smaller and streamlined air intake than the C172.

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