#1 Cylinder High Temps

[wiseng]

Does anyone else out there have an engine were the #1 CHTs are higher ~ 40 F than the rest. The engine is an IO360 A3B6D in a 1978 J model.  I have done all that I know as well as some reputable mechanics.  Change injectors check baffling etc.  It generally runs about 375 while the others run ~ 335.  My understanding is the #3 is suppose to be the hot cylinder on this engine hence the factory CHT gauge.  

 

Anyone find a cause or fix>

[Cruiser]

how do you run the engine mixture?  LOP?

Do a GAMI check to determine which cylinders peak in what order. My guess is you are running #1 Cylinder closest to peak EGT and therefore getting the higher CHT.

#1 cylinder is normally the last to peak. #3 is normally the first on these engines. You can try swapping injectors but it probably will not help much.

[AndyFromCB]

Actually,

 

I would also check the position and type of probes on #3. If the cylinder has two probes because the factory probe is mounted on it in addition to your JPI/GEM probe, then one of the probes will be reading about 30 to 50 higher/lower than the other one. So if #1 is the cylinder with two probes and your JPI is showing 375 and the factory probe is showing 335, your OK. Depending on what type of preheat you have, the JPI probes could be reading lower depending on whether it's a sparkplug/gasket probe vs spring type probe.

 

You might not have a problem at all. My Bravo is setup as above and #5 always shows 40 to 50 degrees less  than the rest due to probe type on #5, but my factory gauge on #5 agrees witht the rest.

 

Also, on my Bravo, #1 used to run hot until I switched injectors around but first I'd verify you're getting correct readings based on probe situation. Just note what the factory CHT says vs your JPI probes when the engine is cold and not running.

 

Andy

[N201MKTurbo]

What kind of probes do you have? are they all spark plug gasket probes? Are they in the thermowells? What do you have for #3?

[wiseng]

I have JPI probes that are screwed in with the exception of the #3 cylinder which has the factory thermowell probe and the JPI is reading temps via a spark plug gasket type.

[N201MKTurbo]

Does it run hot lop and rop? If so it is not a mixture problem.

You might try running it on the ground with the cowl off until the cylinders are hot and measuring them with an IR thermometer. This will prove weather it is a measurement problem. It won't give the same temperatures, but it should give the same differentials.

[wiseng]

Not the CHT probe.  I have switched those around.  it is a airflow issue.  Looking into the suggestion made by Cruiser.

[N201MKTurbo]

Do you mean cooling airflow, or induction airflow?

[wiseng]

Cooling air.  Running Rich or lean of peak gives the ~ same Temp differential between the #1 and other cyl temperatures.  I had Dugosh look at the problem they rechecked the Baffling etc, no joy.  On  leaning my #1 cylinder EGT starts out as the highest but the #2 cylinder always reaches peak first.  Go figure.

[wiseng]

Now that I think about it the high EGT switches between the #1 and #3 on leaning.  It will vary with on which from my observations on density altitude.

[BigTex]

What kind of GAMI spread do you have?  Also, can you upload your data to Saavy Analysis https://www.savvyanalysis.com/home and share the data with the group?

[wiseng]

No fuel flow indication.  I generally have a 20-30 EGT Diff.  Unable to download it is an older model JPI.

[bumper]

Does it run hot lop and rop? If so it is not a mixture problem.

You might try running it on the ground with the cowl off until the cylinders are hot and measuring them with an IR thermometer. This will prove weather it is a measurement problem. It won't give the same temperatures, but it should give the same differentials.

 

Use caution doing high power ground runs with cowlings removed. CHT and oil temps need to be closely monitored (no higher than 400 and 200 F). Problem is cowls are a critical part of the cooling system. When running the engine without them (or temporary ground run baffling), uneven and inadequate cooling air flow will result in hot spots and thermal stress. Cracked cylinder heads can occur in a remarkably short time.

[Alan Fox]

No fuel flow indication.  I generally have a 20-30 EGT Diff.  Unable to download it is an older model JPI.

I thought a gami spread had nothing to do with actual  egt temps , but the times at which they peak in relation to each other measured by fuel flow......Please correct me if I am incorrect....

[wiseng]

I think the GAMI spread is the fuel flow differential to each cylinder.  Understand it should be less than .5 gal/hr.  I have no way of measuring  fuel flow.  Just the CHT and EGT with a JPI 700.  As I stated earlier I have switched CHT probes and get the same temp diff. 

[Marauder]

I think the GAMI spread is the fuel flow differential to each cylinder.  Understand it should be less than .5 gal/hr.  I have no way of measuring  fuel flow.  Just the CHT and EGT with a JPI 700.  As I stated earlier I have switched CHT probes and get the same temp diff. 

 

You should be able to measure fuel flow by taking off the injectors and sticking them in a container to catch the fuel for each cylinder. Run it for a set number number of minutes (depending on your container size) and measure the amount you collected per cylinder and extraploate to gal/hr. You should also be able to see if flow out of the injectors to see if they are partially clogged.

 

I hope it is a fuel flow problem. Replacing an injector is far easier than tearing into a cylinder.

[wiseng]

Dugosh did this when I first presented the problem.  The flow was within Lycoming tolerances.  It is a frustrating problem.  Am looking at reducing the area of the front  top vertical baffle.  Just gathering info at this time on how to proceed.

[jetdriven]

Use caution doing high power ground runs with cowlings removed. CHT and oil temps need to be closely monitored (no higher than 400 and 200 F). Problem is cowls are a critical part of the cooling system. When running the engine without them (or temporary ground run baffling), uneven and inadequate cooling air flow will result in hot spots and thermal stress. Cracked cylinder heads can occur in a remarkably short time.

 

I wouldnt run an engine anywhere near 400F CHT with the cowling removed. If the thermowell probe is reading 400F, I bet some parts of the cylinder are already much hotter, as the cooling airflow is not directed between the fins.

[Marauder]

Charlie's shop is a good one and I would have expected they would have went over the obvious causes. I re-read your original post and it looks like you covered all of the expected causes. It comes down to the basics; fuel, air, combustion & cooling. If the injectors check out, the baffling is fine that still leaves air flow and combustion.

 

Have you done anything with the spark plugs yet? Are they all the same? They do make different ones and maybe one is different on that cylinder. The other problem could be air going into the cylinder. If the air induction is partially plugged on that cylinder, I would expect to see run richer (i.e. lower temps).

 

The only other possibilities involve a possible issue with the cylinder itself. That said, running at 375 is not above that magical panic threshold where we might suspect mechanical issues with the cylinder.

 

Keep us posted.

[Marauder]

I looked up your engine for accepted spark plugs. You should be (I only looked at Champion brand) able to use a REM40E, REM38E or a REM37BY. I found an article that talks about what happens with the different heat ratings of the plugs. Maybe it is simple as a different plug.

 

If not, the article continues on to (sit down when you begin reading this section) the other mechanical causes of higher cylinder temps.

 

http://www.sacskyranch.com/eng23.htm

 

Quite honestly, your temps on that one cylinder are below the threshold I try to stay below (390). If you have a major problem, I would expect you to be in the 400+ club. It may be the beginning of a problem (exhaust valve leak) but hopefully not.

[N201MKTurbo]

BTW, I wasn't talking about running it with the cowl off till it was blasing hot. Just till it was stable at about 1500 RPM, about 250 - 300 deg. Just hot enough to compair the scanner to the IR readings. you think I'm some kind of engine killing Neanderthal?

[jetdriven]

BTW, I wasn't talking about running it with the cowl off till it was blasing hot. Just till it was stable at about 1500 RPM, about 250 - 300 deg. Just hot enough to compair the scanner to the IR readings. you think I'm some kind of engine killing Neanderthal?

 

Nope, I have done that after an oil change.

[mooneyflyfast]

I have this same situation on my 81 J. #1 is the hottest CHT by probably 30 degrees. I run LOP and #1 is the richest (last to peak). Almost all of the GAMI spread is between #1 and the other 3 cyls.

I have quit worrying about it but I figure if I got GAMI injectors so #1 would run leaner the CHT would come down in line with the other cyls.

Maybe the induction system provides less air to #1 causing the mixture to be richer. Anyway, I think this is normal and nothing to worry about.. BTW my #1 has 1900 hrs on it and has never been off.

[jetdriven]

Something I just remembered. The m20j has an upper baffle plate in front of the #1 cylinder. We were also getting higher CHT on #1 so I took that baffle of and duplicated it, except 1/2" shorter and put that on. It lowered CHT #1 30 degrees or so. The final adjustment was a small piece of baffle seal material between the cylinder head and that baffle to allow a bit more air through. That did the trick. You can also adjust the other CHT's by creating a gap at the baffle like that.