RV-10/IO-540 CHT Advice

[SAAFNAV]

Hi all,

I'm flying a new RV10, and no. 5 cylinder is running hot. Issue 1 is corrected, in that the redline was set at 230C instead of the approved 260C as per the Lycoming manual.

Is there anyone in the JHB/Pretoria area that are well versed with these planes and willing to fly with me in the week to give some advice on getting the engine to settle properly?

Thanks a lot!

[sweptwing]

For starters, please change your measurements to Fahrenheit so that we can compare apples with apples. It’s like flying in meters when everyone else flies in feet.

Give it lots of air (speed) and lots of fuel and if it’s still close to the red and not coming down over time as it’s running in you need to look at your baffling.

[lampiesJR]

How much hotter is no 5 running than no 6?
Have you tried swopping no 5’s probe with no 3’s probe to see if the problem moves with it?
If not the probe, check blowby’s after the flight.
Check the surrounding baffling.
Get an AP to check the fuel flow to the injector. If similar to other, it might be the injector itself.
Keep us posted!

[Chalkie]

Hi all,

I'm flying a new RV10, and no. 5 cylinder is running hot. Issue 1 is corrected, in that the redline was set at 230C instead of the approved 260C as per the Lycoming manual.

Is there anyone in the JHB/Pretoria area that are well versed with these planes and willing to fly with me in the week to give some advice on getting the engine to settle properly?

Thanks a lot!

260*C is 500*F you really do NOT want to go there as that sort of temperature anneals the aluminium alloy, which causes cracked heads.

232*C is 450*F. That figure is the one recommenced as the max continuous in cruise by Mr Lycoming. Use that as the preferred maximum.

Does this RV-10 have louvres added to bottom or sides of the cowl? All RV's are tightly cowled to reduce cooling drag so some do run hot, especially engines with lots of friction wearing the cylinders and rings in the run-in process.

For whatever reason, the right rear cylinder is usually the hottest in a Lycoming, so on initial flights keep the ground running time to an absolute minimum, then leave mixture full rich and climb as fast as possible (high speed not high ROC) as soon as possible. When power down to close to 75% power, rapidly and aggressively pull the mixture to PEAK EGT. This will cool the cylinder heads considerably.

I have said it before: study the Lycoming graph in the engine manual for EGT / CHT / percentage power / BSFC you will see CHT peaks before EGT, so at peak EGT the CHT runs about as cool as 150*F ROP.

Sorry, I should have said, the idea is to run the engine 'over square' so that the piston rings can be forced hard against the cylinder walls. This is not always possible on the Highveld. What you do NOT want to do is maintain high RPM 2600 - 2700 as the linear speed of the piston and rings just makes a lot of friction heat. Leave throttle FWO and pull RPM down to achieve 'square or slightly over-square' whilst still trying to maintain more than 75% power. Once you start leaning, the percentage power will drop off quickly.

BELOW 75% POWER, YOU CANNOT DO DAMAGE TO THE ENGINE BY LEANING. Mr Lycoming says that...

Running CHT's to 260*C will do damage and glaze the cylinders. Fly safe...

EGT-CHT-PWR graph.doc

[SAAFNAV]

Hi all,

Thanks so much for inputs.

Some details about the engine:

Brand new, 25hours and doing oil change on Monday. We are going to try Philips oil, and also inspect for metal particles and possibly a boroscope inspection.

The thermocouples were changed around and gives the same values, so no problem there.
Fuel injectors were benched-tested and within limits - we also took out the injectors on 1, 3 and 5 to do a flow rate test at full throttle and mixture. All were pretty much the same, so no problem with the divider either.

Some values I have handy now:
In the climb I get 239 C (460F) on No. 5. No. 6' EGT is the highest, I get 821C (1510F). The temp increase is quite fast, and I guess it will increase beyong 250C, but I come back on the power/enrichen before that.

In the cruise at 75% (24 inHg/2450-2500rpm) I get 210C (410F) and she's reasonably happy.

At the moment I'm running mixture a bit rich, was still a bit scared to go too lean, but will study that Lycoming manual in depth and report back when I fly her again.

The engine and baffles were all as received from Van's, and the previous plane I flew didn't have such issues, but I will see what we can do around No. 5 to increase air flow if we need to.

Thanks for help so far,

Regards,
Erich

[Chalkie]

At the moment I'm running mixture a bit rich, was still a bit scared to go too lean, but will study that Lycoming manual in depth and report back when I fly her again.

The engine and baffles were all as received from Van's, and the previous plane I flew didn't have such issues, but I will see what we can do around No. 5 to increase air flow if we need to.

Thanks for help so far,

Regards,
Erich

Erich, do not be scared of the red knob. At 75% power, ROP, if you pull the mixture back to PEAK EGT. You CANNOT damage the engine and you will be pleasantly surprised to see how much the CHT reduces, yes percentage power will also reduce.

The graph posted above shows clearly how CHT decreases as you reach peak EGT and go LOP.

I have said it before and I will say it again, check the graph the CHT at PEAK EGT is the same as about 150*F ROP. To cool a CHT with ROP you need a hell of a lot of fuel not to cool but to SLOW DOWN COMBUSTION so that most of the burning fuel goes out of the exhaust.

Leaning to peak EGT does the same and does it cleaner and cheaper.

You mention improving airflow to No 5 cylinder. Did you or the aircraft builder fit the small baffles facing the airflow directly in front of the No 1 and No 2 cylinders? (You can see them through the cooling air inlets) If you did, remove these. Do your engine a favour. Van advises that these only be fitted to a well run-in engine, and then trimmed to adjust CHT's to make them more even.

[SAAFNAV]

Hi Chalkie,

Flew again today after the oil change. Might be bit biased, but seems like the temps are a bit down.

I flew her like you suggestion and leaned it properly (I guess you get talked scared when you fly a Cherokee with no EGT indication), but I ran her at peak EGT and all seemed very normal.

During take-off the CHT's ran high, but only after passing 1 000'. I stopped the increase in temp at about 240C, but in rise wasn't as rapid as earlier.

The cooling air intake is open all the way, just with those 'baffle plates' (for lack of a better term) between the pots.

Thanks for all the input guys.

Regards,
Erich

[Chalkie]

Hi Chalkie,

Flew again today after the oil change. Might be bit biased, but seems like the temps are a bit down.

I flew her like you suggestion and leaned it properly (I guess you get talked scared when you fly a Cherokee with no EGT indication), but I ran her at peak EGT and all seemed very normal.

During take-off the CHT's ran high, but only after passing 1 000'. I stopped the increase in temp at about 240C, but in rise wasn't as rapid as earlier.

The cooling air intake is open all the way, just with those 'baffle plates' (for lack of a better term) between the pots.

Thanks for all the input guys.

Regards,
Erich

"With just those 'baffle plates' between the pots"

If that means: "Looking in the front, through the cooling air inlet apertures you can see two vertical flat plates riveted to the baffles and shaped like the cylinder and cylinder heads; in front of the cylinders."

Then those things should not be there. They should be fitted to a well run-in engine, not a new running-in engine. Not my advice; Van's advice: it is in the plans that come with the baffle kit.

Phillips 20W-50 will bring oil temperature down about 10*C compared to a straight SAE 50 oil. I suggest using the Phillips M until 50 hours.

On your PA28 with no EGT, pull the red knob till the engine splutters and coughs, then advance slowly till it runs smoothly and leave it there.

Fly safe.

[SAAFNAV]

If that means: "Looking in the front, through the cooling air inlet apertures you can see two vertical flat plates riveted to the baffles and shaped like the cylinder and cylinder heads; in front of the cylinders."

No, it means looking from the top down into the engine with the cowls removed, there's some airflow deflectors between the cylinders. Apart from them, no other obstructions.

Thanks again for the help.

[Chalkie]

If that means: "Looking in the front, through the cooling air inlet apertures you can see two vertical flat plates riveted to the baffles and shaped like the cylinder and cylinder heads; in front of the cylinders."

No, it means looking from the top down into the engine with the cowls removed, there's some airflow deflectors between the cylinders. Apart from them, no other obstructions.

Thanks again for the help.

Great. Fly safe...

[Chalkie]

How about a report back, now that you are (hopefully) comfortable moving the red knob back?

[Chalkie]

If that means: "Looking in the front, through the cooling air inlet apertures you can see two vertical flat plates riveted to the baffles and shaped like the cylinder and cylinder heads; in front of the cylinders."

No, it means looking from the top down into the engine with the cowls removed, there's some airflow deflectors between the cylinders. Apart from them, no other obstructions.

Thanks again for the help.

Great. Fly safe...

No feedback?

[ppakotze]

What efis are you using? Had cht over reading due to selecting wrong cht thermocouple for the efis. Corrected the setting and cht dropped 50f. Remove one and dip it in a kettle while boiling. Should read 100degC or 212f.

Regards