What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Hot Cylinder #6

J Twilbeck

J Twilbeck

Well Known Member
So, I've been flying for a few months now and have an issue that I'm not sure how to solve. All of my temps are really great except cylinder #6. It is almost always 20 degrees hotter then the rest. So lets say during a flight I get 380 on all of the other cylinders I read 400-410 on cylinder 6. Leaning helps cool this cylinder down but it never settles down to what all the other cylinders show. This is the cylinder that sits right next to the oil cooler opening. And my oil temps are actually a little low. Running around 165-170 during cruise.

- Yes I tried swapping the CHT probes and I got the exact same readings. So that's not it.

- Do I install an oil cooler flapper to increase the oil temps and maybe force more air around cylinder 6 to cool it?

- Should I try restricting the airflow to the oil cooler at the opening, just block some of it off with a strip of aluminum, reducing oil cooler flow and forcing more air around cylinder 6? This is a much easier to install solution.

- Is there something else I'm missing?

Any help would be appreciated.
 
On any install, recommend adding a butterfly valve inline with the air to the oil cooler, like this one: http://www.averytools.com/prodinfo.asp?number=1503

On most flights I end up closing down the butterfly valve to keep oil temp up into the 185-190 range. I note that this also provides come #6 CHT temp reduction. It is a must have for winter ops.

If not already done, recommend balancing the cylinder injectors. On my stock Van's engine I had a 1.0-1.2 GPH spread between first to peak and last to peak. This made any LOP operations rough. After a few data runs and injector nozzle replacement the spread is now down to 0.1 - 0.3 GPH, and LOP is smooth. This provides the best way to operate your engine in cruise and keeps CHT much cooler than ROP ops. Injector nozzles are available in multiple sizes from Air Flow Performance at $21 each.

Do the balance first and see if you helped the #6 CHT temp issue before you start doing baffle changes and such.

Carl
 
What is the EGT on that cylinder? Leaning should not make the CHT cooler unless you have an induction leak and are already running close to peak EGT on that cylinder, and leaning would therefore make that cylinder lean of peak which would cause a CHT reduction.

Check the #6 cylinder intake pipe gasket for cracks/leaks.
 
EGT is right in line with the others, around 1360, it does not stick out as an oddball. I should clarify that leaning brings all the CHT's down and there is no major delta with cylinder #6. But it is my "flagship" in that it's the cause for all my engine operations because of it running so hot.

With no difference in EGT's do you think that intake gasket could still be an issue?
 
J Twilbeck said:
EGT is right in line with the others, around 1360, it does not stick out as an oddball. I should clarify that leaning brings all the CHT's down and there is no major delta with cylinder #6. But it is my "flagship" in that it's the cause for all my engine operations because of it running so hot.

With no difference in EGT's do you think that intake gasket could still be an issue?
Click to expand...

If the #6 EGT is normal it is not likely to be an induction leak, but it is easy to visually inspect. You may want to try and install an air dam in front of the #2 cylinder, and make sure there are no big air leaks around the base of the rear cylinders if you have not already.
 
First things first. One response assumes fuel injection, the other assumes carb. Which do you have?
 
Even though the EGTs are about the same that doesn't mean that #6 cannot be leaner than the rest. Absolute EGTs don't matter all that much. Where they peak relative to each other is what matters most.
Go to 24/2400 and do a slow mixture sweep to see where they all peak and then check your data on Savvy. That way you'll know for sure if #6 is leaner or not.
 
The needed info is where each cylinder is operating relative to each cylinder's peak EGT. This (your situation) is exactly what I would expect if #6 is 50 rich of its peak egt, while the others were operating right at, or lean of, their peak egt.
Absolute numbers don't mean much, we need to know peak egt for each cylinder and where you are running relative to that.

edit: What Lenny said
 
Last edited:
J Twilbeck said:
- Yes I tried swapping the CHT probes and I got the exact same readings. So that's not it.

- Do I install an oil cooler flapper to increase the oil temps and maybe force more air around cylinder 6 to cool it?

- Should I try restricting the airflow to the oil cooler at the opening, just block some of it off with a strip of aluminum, reducing oil cooler flow and forcing more air around cylinder 6? This is a much easier to install solution.

- Is there something else I'm missing?

Any help would be appreciated.
Click to expand...

From a general root cause/troubleshooting standpoint, you may want to confirm if airflow bypassing the cylinder for the oil cooler is indeed an issue here. You could try blocking air flow incrementally to the oil cooler with metal tape to see what effect that has before committing to installing a butterfly.

I would consider placing temporary thermocouples at the downstream position of selected cylinders to see what variation exists in the "used" cooling air temps.

What about measuring static pressure above the cylinders to see if there is a large variation?
 
The engine is fuel injected.

Hopefully the Savvy image attaches correctly. This data was from a normal cruise climb on one of the short trips we did and shows the leaning from ROP to LOP duration.

You can see the FF in relation to EGT's during leaning and the CHT's in the lower half of the graph.

Then the graph below the first is the Gami spread.

Is there something I'm not seeing?

Temps%2B2.JPG


And here is the GAMI spread:
Temps%2B3.JPG
 
Last edited:
Those GAMI spread lines are kind of arbitrarily placed by the software. Look at the chart instead. To me it looks like it peaks at 13.5 or so.
I'd do a couple more runs to confirm though, level 24/24, stop every .2gph for a few seconds for the numbers to settle.

You have about the same CHT delta when LOP. So it may still be a cooling airflow issue.

Lenny
 
J Twilbeck said:
So, I've been flying for a few months now
Click to expand...

Holy cow, congrats Justin! Did I miss first flight announcement here? I just checked out your blog - plane looks fantastic!! I will PM with a question about your interior lighting as not to totally derail this post:D

Big congrats on a flying -10!
 
60av8tor said:
Holy cow, congrats Justin! Did I miss first flight announcement here? I just checked out your blog - plane looks fantastic!! I will PM with a question about your interior lighting as not to totally derail this post:D

Big congrats on a flying -10!
Click to expand...

Thanks, no you didn't miss the announcement I just haven't posted it yet...:eek:.
But thanks for the compliment.
 
Justin,
A couple of observations and questions

I consider anything over 400 degrees too hot with the acceptation of a short blip. During the summer, I can not climb full throttle to altitude without one of the cylinders going above 400. I find that climbing out at 125kts seems to be the best speed for cooling and reducing the power once over 2000 AGL. Maintaining 24/2500 produces CHTs in the 350-380 range depending on the OAT. I never lean on climb out to less than the takeoff EGT.

When you are on the ground and the engine is cool, does the CHT read the same as the OAT? How many hours do you have on your engine? It seems that mine took around 15- 20 hours before the CHTs dropped and stabilized. To me it looks like you have a problem with all the CHTs being way to high, but #6 does seem way out of line. FYI, my #6 is one of the coolest cylinders. The oil cooler damper position has little affect for me.

Is this a new Lycoming factory engine? Do you have your wheel pants and fairings installed. Installing them and increasing your airspeed will increase your cooling. I would still check for an intake leak and make sure that your baffle seals around the rear and lower portion of the #5 and #6 cylinders are tight up against the cylinder. I would also check your timing advance. I just looked at your Blog and see you have dual electronic ignition.
 
Last edited:
J Twilbeck said:
Thanks, no you didn't miss the announcement I just haven't posted it yet...:eek:.
But thanks for the compliment.
Click to expand...
Congratulations! It looks great! I have been following your blog but for some reason (browser cache?) your updates haven't shown up for me. I just upgraded my phone which cleared my cache and allowed me to see everything past "We got a hangar" for the first time today.

Anyway, once again congratulations!
 
It appears to me you may be leaning to rapidly to get good data. Note how some CHT's appear to be still rising until :18.5 when there was a sudden drop of 1 gal/hr in FF. (If CHT's are rising you must still be ROP).

Electronic ignition? Something else to look at. Even a few extra degrees of advance can significantly increase CHTs. Any chance #6 could be timed differently than the others?

Maybe trouble shoot at lower power settings. I wouldn't run a cylinder at 440 no matter where Lycoming puts the red line.
 
You must log in or register to reply here.
Back
Top