Normal CHT, EGT's range in cruise?

[N8632Y]

Wondering what temps people are getting for normal flight profile at cruise and running about 60-70%.
EGT's and CHT's, in summer, ie warm weather.

Reason, How can 2 twins run so different?
I'm looking for a problem with his digital gauges

I average 375 CHTs, 1490 EGTs, in my twinco.
He gets low 300 CHT's, and 1300 EGT's.

We have to go back and re run his numbers more controlled, but do the EI digital gauges run much diff than the JPI in the twins?

steve

[N3322G]

Steve,

Can't say exactly why but can tell you from experience ... Mom was an instructor at the local FBO which was also a Piper dealer distributor back when Comanche were in production. Cross country races in those days were speed races with handicaps set on manufacturer specs so what Mom would do is fly all the new Comanches delivered to the FBO and see which one was fastest and then borrow it for the event.

You might be surprised, maybe not, at the wide variance of those birds coming straight from the factory ... as much as 5 knots and they couldn't have been any more stock at that time. My point is, I wouldn't expect the CHT and EGT readings to be the same in my Twin with anyone else's.

In terms of what you are seeing and your question about the EI vs JPI gauges. Might ask the same question on the MP and RPM gauges - are they really giving you the same MP and RPM across both planes?

Also, the positioning of the EGT probes in particular can dramatically impact the readings ... so can the CHT probes. To be FAA Airworthy the #3 cylinder has to have the JPI and 'Piper' probe to run both instruments so it reads 30ish degrees colder than the other cylinders in my Twin.

If I were going to test and compare, I'd run at max power at the same density altitude with the same weight and CG with same mods and same flexible baffles. I know just plugging the holes between the fixed and flexible baffles on my twin in 2006 dropped the temps 20 degrees at the same power. Got another 25-75 degree in 2009 drop after the improved flexible baffles - don't have as good data for that one.

Anyway, there are lots of factors beyond just the JPI vs EI gauges to look at and hopefully I've tossed out some thoughts that are helpful. I'm sure others will chime in and mention age of engines etc.

[steen]

Steve,
As Zach says, they's the same but they's different.
I have friends who fuss about CHTs, EGTs, oil temps, etc. but I know some who don't have those concerns, all flyiing "identical" PA-30s.
First of all, aircraft temp. displays are not known for being exactly accurate. I use mine to make sure no limits are exceeded, but my CHTs don't exceed 350 nor does the oil temp go above 185 with the cowl flaps closed even in hot summertime. In winter my cruise CHTs are showing below 275-300 and my oil temps can't get over 150-160....too cool. I don't know why Piper did not include oil cooler winterization plates like they did for the other planes.
I have seen a wide range of baffles and engine-cowl seals and, I've said it here before, I believe some temp problems (and speed losses) are caused by less-than-perfect baffles. A thumb sized hole lets a lot of air go by without cooling and increases drag thru the engine compartment
Steen 7997Y

[Tony Scarpelli]

Variance between gauges not withstanding:

Make sure your injectors are clean, clean, clean. (are you running the same plugs?) They should be cleaned every annual but when I got my Comanche they were nearly blocked which resulted in cracks in 3 jugs.

Make sure your MP guage gives you what you would expect (is accurate at known levels).

Make sure you are not putting up with one (or both) bad or marginal mags.

Once you know you have done all you can, then don't worry about it. Just note the difference. I had a 150 dF diff on my EGT probably due to aging thermal couple. It seems strange that 8 TCs would be off that much and still be in sync relative to each other.

[N8632Y]

To all that posted so far: ALL GOOD POINTS!
And I know all gauges and planes are not the same, and position of probes give different readings, etc...
BUT, my plane gives me approximate book numbers, and values in a range, yes, but then there are limitations to those numbers, such as I warm oil, cht's to green before runup in winter, try to get oil temps above 160 in winter at cruise, and on a trip, set power, and run "lean find" and the numbers coincide to the book w/in reason, and if not, then why? Is it the gauge, and I cannot trust the gauge, or the gauge is right and I have a cracked plug, etc.
So in my twin, at 3000 msl, set power for 55%, run lean find, and peak at 6.8 gph/side, then i'm reasonably close.

Now go fly with my friend in his twinco, set up the same, run lean find, and the peak comes in at 4.5 gph/side, then my radar goes up? Then I look at EGT and see numbers in the 1100's? Where I'd be at least 1400, So I'm trying to get ideas, ballparks, not exacts...

Yes, we have to go back and run controlled tests, like you set up for "PreGami's".....
Still looking....
Will post if i get anywhere.
steve