Cylinder Head Temperatures

bigfatflyer · January 2

Hello and Happy New Year everyone,

One of my new years resolutions this year is to address cylinder head temps over 400 degrees.

I have a 1964 Cherokee 180 with the Lycoming 0-360 A3A engine. I installed a JPI 830 engine monitor a while back. My cylinder head temps routinely go above 400 degrees on climb out unless I pull power and reduce climb angle. Its easily managed this time of year, but summertime, I just let the heads heat up, trading altitude for head temps.

If I choose to cruise at 2400 RPM, the head temps hover right around 400 degrees the whole time.

I have replaced the baffle material, as it was tired. That had zero effect.

I guess my question is: Am I chasing the wind here, and the head temps are gonna be high with this engine/airframe combo despite my best efforts??? Anyone have this engine/airframe with a engine monitor to compare with???

I have not explored sealing every small gap of the baffles where they meet the engine. I guess I was wondering if that would have a significant effect.

Thanks for any insight or suggestions from the group.

jacobsja · January 2

Apologies for not having a solution and just want to state that you are not alone.

Will need a better expert to validate, but isn't the O-360's cylinder head temperature threshold a bit higher than that?

Used to have a late 70's Archer and it also had higher CHTs during the take-off sequence. This went on unnoticed for a long time until the OE single probe EGT was replaced with a multi-probe JPI analyzer. Do not remember the exact numbers or cylinder, but it was in the 400 range and enough that the round gauge JPI would alarm on CHT temp during climb to TPA.

Plane was on lease back and the lessees were in control of maintenance (note to self: NEVER allow the lessees to have absolute control over the leased asset's maintenance again). Even after the JPI installation, either the CHT warnings were ignored, or the JPI was ignored completely, until an owner happened to take the plane for a flight. As the lessees did not want to spend money, they decided to fix the high CHTs during takeoff by issuing a policy that once clear of obstacles, to lower the nose and raise the speed to at least 90 if the JPI alarmed. This practice was effective as the JPI stopped its alarm on CHTs.

While that engine did not go to TBO, it was other power management issues that likely accelerated its wear as the heads were reused during its subsequent rebuild. Am not trying to state that the 400* CHTs are all that great, but rather convey that you are not alone.

empannin · January 2

Hi, I would also take a close look at ignition timing. If the baffles are good the next items to explore are timing and mixture. Even slightly advanced timing can impact CHT's. Have you done a GAMI lean test? No injectors in a O-360 but it can still be instructive on fuel balance. Also, what happens to CHT's if you run richer or LOP?

If all your cylinders run hot it is more likely a systemic issue vs localized baffling. This could be a problem with the cowl entrance or exit paths but unlikely on this plane. How about the oil temp and oil cooler airflow?

Are the CHT probes on the sparkplug gasket or in the probe well on the underside? Sometimes if not a primary instrument the probe that is primary is in the probe port and the electronic instrument uses a spark plug gasket for reading temp on that cylinder

bigfatflyer · January 3

Hello,

I will try to answer the questions from both of your comments in this comment.

Jacobsja,

The threshold from Lycoming, I think is MUCH higher than 400, I want to say 450 degrees or so, but I am trying to take Mike Busch's advice and keep head temps below 400. Good to know that I am not alone.

Eric,

Just out of annual, so timing was checked then and its always been spot on. I have not done a GAMI lean test.

Full rich on climb out, but back cylinders, usually cylinder 4, reach 400+. It makes sense that the back cylinders get higher first, just due to physics, as front cylinders block some of the air to the backs.

Oil temp is usually around 160 to 170.

Probes are on the bottom of the head, NOT the spark plug base type.

empannin · January 3

Check the baffling on the back cylinders. Due to the cylinder design there needs to be a little space between the baffle and the fins otherwise the back right one in particular is blocked. I think the gap should be ~ 1/8 to 1/4 of an inch.

The goal is to convert the velocity of the incoming air into pressure and this slightly pressurized air should fairly feed each cylinder. This goal goes sideways so many different ways in practice.... There should probably be an upper or upper/lower plenum pressure gauge that would help troubleshoot cooling but I am not aware of any certified plane with one.

planewrench · January 6

All good comment above, when was the last time the carb was gone thru, very possible its running a bit lean on the full open schedule where it should be adding additional fuel at the full open position. We weirdly call this the "economizer" as it leans out once you come back to 75 percentish.

carl

VanderWerf · January 6

Lycoming engine CHT temp maximums is more like 420, higher than Continental, but not as high as the 450 suggested above. Always better to keep below 400 if possible. Hot day, low altitude climb may regularly drive CHT temps above 400. I live in Colorado Springs. Airport altitude over 6,000 ft. Very difficult for me to get above 400 here.

jolexa · January 6

I’ve attached a picture from the lycoming manual. To summarize: 500 redline. 400 continuous. https://www.lycoming.com/sites/default/files/attachments/O-HO-IO-HIO-AIO%2520%2526%2520TIO-360%2520Oper%2520Manual%252060297-12.pdf

On my 1979 Archer, I don’t get concerned about 420 on climb out. In cruise, I like to see 380-400 depending on season. I’ve been chasing CHTs recently (new baffles, attacking gaps with RTV, etc) and I’ve come to accept that below 400 at all times is unreasonable. Heck, this plane only had a single EGT probe for 43 years and it was fine. Now my GI-275 full cylinder monitoring is just telling me what it always use to do, can’t change an old bird I guess. Well, I think I’ve made it better so far.

So, if you want my opinion: fly on. :-)

hschulman · January 10

Just an interesting note, Continental has a service letter addressing the use of RTV on the engine baffles. I called Lycoming about it, they highly recommend sealing the baffles, but they will not issue a service letter because they consider the baffles part of the airframe. As jolexa pointed out you are well below the max temperature, I would not loose any sleep over it, but I would be generous with the RTV. One more thing make sure the interbaffles are properly positioned.

spikecarter · January 14

Of course the OEM indicator for an 82 Archer, only has an EGT gauge, which presumably is not quite the same as CHT. And that gauge doesn’t even have numbers, just “tics”. Not sure if they translate. I’ve always just leaned to peak and dropped it back a bit. Like VanderWerf, I live in Pueblo,CO, always above 6000’ and only full rich to start.

planewrench · January 14

So lets see here, at 6000 msl not including density, what percent power are you running at with 2400 rpm?

carl

planewrench · January 14

My comment directed to big, wondering where he is located. carl

Resq5hvy · January 19

I have a question about my Arrow. My CHT’s are always 290-340’s. Are my numbers believable? Yesterday it was 10*F outside burning 10.2-10.5 GPH 295-315 in cruise flight. Only flew at 20”MP to stay out of the yellow and 2500RPM.

Is it possible my engine is running so cool?

planewrench · January 20

Well it would be nice to see the higher end temp for better lead scavenging overall. If it was 10 on the ground, was that the OAT in cruise too or was it colder. MOre impt, what was your oil temps.

carl

jacobsja · January 20

My CHTs also run in the upper 200 to mid 300F range. OAT does not seem to matter. But this is not necessarily a direct apples to apples as I have the the 32 cowling which is a bit different than the 28's in the discussion.

To the oil temp angle, it ranges from 180 - 183 F at all OATs.

Possibly related is that I usually cruise under 75% power and LOP.

For lead scavenging, recent bore-scope inspection came back with zero concerns and positive comments.

planewrench · January 20

Good to see the oil temps are at least that,, a bit higher would be good but as long as you are not draining water on the ground its a good sign., Despite LOP, chts in the 200"s?? That seems uncommonly low. Sure your gage not showing Centigrade?? LOL.

Carl

Resq5hvy · January 20

It was 10 at cruise. It was an instructional flight I was in the back seat, when asked she reported in the green. Her husband is her instructor and he just got home from indoc at SW so we took a celebratory flight around Ohio.

I am flying tomorrow, it will be in the low 20 upper 10 s up high. I will take photos of the JPI Jr Flight Engineer panel. You can see my temps. New mags and occasionally get Pb fowling.

planewrench · January 20

Ya, that would be interesting. Just seems odd that your cht is just barely above oil temps... carl

jacobsja · January 21

For my CHTs, key word is "upper". For a more precise number, in the 290s for the coolest heads. So really not much under 300. The heads do not have too wide a range from each other and do not get any comments about this when sending the data in for review.

planewrench · January 21

If i can un thaw my 172 this week i'll take a comparison shot. Carl

Resq5hvy · January 21

I got a few photos, all cruise flight, some working the engine a little hard than others. All photos were after the power had been set for several mins.

The sun was out today.

planewrench · January 24

Holy cow batman, LOL. At that OAT i dont even want to come to work here in MSP! I see that the factory oil temp showing almost 200, any idea were the probe is for the monitor, i suspect in the fwd nose galley? Carl

Resq5hvy · January 24

The CHT screws into the Lycoming port, I was not there when the A&P installed things.

Oil temp of 170ish is lower than some like. I get 185-190 in summer. The oil prob I think is in the front of the case but not positive.

I think it is a JPI 830/930.

planewrench · January 24

Reason I ask is in the last lower phot, you see the factory oil temp is hitting closer to 200, which is excellent. The factory sensor is on the oil filter adapter, i suspect the jpi sensor is located in the front of the eng in the galley end plug. Carl

Resq5hvy · January 24

On the Piper gauge? I think it is pointed at 180.

planewrench · January 27

Yeah, thats what i was looking at. The factory one. It would be nice to see that above the 180, but given the OAT, not sure you can cover enough to bring it up. If water/slim not draining out of the breather, you doing ok. Carl

Resq5hvy · January 27

@planewrench

Thank you for your thoughts. It goes in for annual in a few day…and a new prop, I have the original with the AD. One of the issues is tightening the bolts on my engine case to reduce the territorial marking habit my plane has. So looking for places and reasons for oil leaks is on the list. He plans to pull the data off the JPI and see if it is running too cool.

We may put the winterization block off port on it as we look to have another cold snap coming mid February. I am unclear if I am allowed to remove the port as the owner operator or if it must go to the A&P with log book entry.

planewrench · January 27

winter plate are not mechanic rated. You will certainly know if you have it on too long! Carl

Resq5hvy · January 27

https://piperowner.org/talk/discussion/comment/1444850#Comment_1444850

Great. It is easy enough to remove it.

Cylinder Head Temperatures

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