Any piston gurus out there?

[Rally]

Just wondering. On a small 6 cylinder engine like a 0-300 what is a normal EGT spread for a healthy engine. Whats a maximum limit before you suspect something is wrong?

Thanks

 

[CDVdriver]

Textron Lycoming website recommends 50F rich of peak.

Peak egt will vary with outside air temp.
Somewhere around 1400F does it for me most of the time.

 

[Rally]

Actually I am refering to individual EGTs for each cylinder. The maximum difference between the lowest EGT and the Highest EGT between two cylinders.

Thanks

 

[GravityHater]

The egt probes are not very reliable for actual values, but they are great for noting *changes* in an engine.
For ex., the reading may be '1350F' but because of positioning and probe error, the actual temp may not be very close to that at all. (CHT readings however ARE usually fairly reliable indicators of true temperature in the head.)

Anyway, as for maximum spread which is what you asked for;
I suppose if you had one cylinder that was ALWAYS 150F lower than the others it MAY be just fine.
But if all cylinders were within 50degrees for a long time, and suddenly one was 150F lower - I would look into it.

I am told, and have seen, where most serious cylinder problems will make the EGT drop right off the scale. But it is also possible that a plug goes bad, or an injector gets partially plugged and the EGT may rise (yes, I mean rise) only a little (maybe 50F?) [watch the egt rise next time you do a mag check for proof]

I fly an IO520K and the EGT has always varied by 100F from hottest to coldest and the engine is running great for 700hrs now. The CHTs however are within 50F in cruise.
Always consider the other factors when interpreting EGT changes.... how does it sound and feel - how is the power output, response to throttle. Other panel indications?

Finally as to the other post and the manufacturers recommendation of 50F ROP... .many now feel that running an engine at 50ROP will have the engine at it's hottest and will not maximize the engine's lifespan. Deakin's articles on Avweb go into great detail on this. I think to run 50ROP with only one EGT probe is risky. With all-cyl probes (CHT and EGT) you can do it - but consider the graphs that Deakin posted before you do this.

 

[DisrespectedJ32]

The value you need to consider is not EGT but CHT (cylinder head temp).

If you have a engine monitor such as a EDM or JPI, the most important perameter is CHT. As long as the coldest and warmest CHT's are within manufacturers limits you are ok.

If 5 of 6 cylinders are within CHT limits but the 6th is not (runs hot/cold), you need to have a mechanic check it out. You will probably need some work.

To answer your question, the maximum CHT spread would therefore be the upper and lower CHT limits set by the manufacturer. Say 175 F to 475 F.

If you have an engine monitor, a sick jug will become apparent very quickly.