High CHTs

[lr172]

Originally Posted by kaa

Thanks everyone for suggestions, appreciate it.

I'm pretty sure the thermocouple type is set up correctly. Before the engine start all temperature sensors read ambient, as expected.

Here is some data from the first pattern at the time of initial throttle back (first number is the absolute value before throttling down second is the difference between partial throttle and full throttle):

Time: 00:12:44-00:13:01
EGT1: 1445°, 35°
EGT2: 1340°, 110°
EGT3: 1335°, 70°
EGT4: 1310°, 80°
MAP: 28.4, -6
CHT1: 421°, -5°
CHT2: 422°, 0°
CHT3: 429°, -4°
CHT4: 451°, 2°

There are more instances like this in the graphs (the link is in the first message).

It does look like an intake leak as several people noted here. I'll take a look at the carb attachment and report back.

(heh, always wanted a data logger)

CHTs do not seem all that unbalanced. My #6 is 30* hotter than others on my 540 and my #4 is 20* hotter than others on my 320. I would expect EGTs to drop in those scenarios (with a carb that is leaned via the red knob, air fuel ratio typically increases as throttle is pulled back, lowering EGTs), so it is likely that you have intake leaks. Reducing MAP will increase the amount of leanness due to a leak. While a carb gasket seems likely here, it is not uncommon for ALL of the intake gaskets to fail, especially if they were not re-torqued early in there life. You can spray carb cleaner near the potential leak points and listen for changes.

Getting 420 CHTs in the first minute after T/O is a problem. Could be either poor baffling or a lean mixture, due to too small of a main jet. What are the EGTs when reaching pattern altitude after take off?

[RhinoDrvr]

I recently upgraded from UBG-16 to Garmin G3X, and saw a 50 degree increase in CHT's. I was hovering around 390 in climb, after the upgrade I was seeing 440. My mechanic was suspect of the sensors.

We closed up the intake ramps, redid the baffle seals, and cleaned up the seal design around the spinner. Temps came down 40 degrees or so. Now even on a 110 degree day, I can climb at 120kts with the hottest cylinder at 395 degrees. In cruise the temps come down about 20-30 degrees.

I would take a hard look at your cooling setup, since in my case the temperature delta seen between the EI and the Garmin proved to be accurate.

[kaa]

I repaired a few small problems in the baffles, and it took ~10 degrees off the max CHT in climb to pattern. Still the maximum is at 440, which is too high for comfort. Today's flight: https://apps.savvyaviation.com/fligh...3-c0bead8909e3. I flew with MP disconnected from the p-mags just to make sure that variable timing doesn't do weird things to EGTs.

The EGTs rise when throttle is pulled is still there (not surprising since I haven't changed anything). I tried to find an induction leak using the shop vac method, and the only thing I found is a leak around the carb throttle valve shaft. It looks like this: https://photos.google.com/share/AF1Q...huXzRncGpVQ3RB.

Everything else seems fine, at least no obvious big leaks anywhere.

The valve shaft wobbles a little bit, enough to see, but I could not record a good video to show it, so it's not too much. I know some play is acceptable, but are leaks there expected, or is it time to overhaul the carb?

[kaa]

I installed an overhauled 10-4164-1 carb, and nothing much changed. The fuel flow went from 15 to 17.5, so that's nice, but the CHTs didn't seem to drop much (just consistent with a cooler day). I rechecked the baffles, and most of them look ok, but there are big holes (pretty much the absence of a baffle) around the bases of cylinders 3 & 4 (where they are smooth with no fins). I'm not sure how it is normally set up though.

I'm starting to question the intake leak theory though. Perhaps the EGTs rise when the throttle is closed enough for the idle circuit to kick in, and it seems to be adjusted too lean?

The data is here: https://apps.savvyaviation.com/fligh...c-0cc9ad3cfca8

Would anyone have pattern flight data from a carbureted O-360, just to compare?

[sailvi767]

I just went through chasing a similar problem in a IO540. I was certain I had intake leak issues as I had rapidly rising EGT’s on throttle reduction in the pattern. It turned out the induction system was fine. What I did have was a loose wire cap on one mag and a bad plug on the other mag. Neither showed up on a traditional mag check. In addition I am actually running a bit rich at takeoff fuel flows but am hesitant to address that with the current high temps. I did not however have CHT issues. I would run a high altitude mag check with the mixture as lean as you can get it.
G

[Walt]

The older EI cht probes are known to read on the low side, up to 30-40deg, so seeing an increase after changing to the bayonet style probes is normal. I just did a swap from the old to the new style on my own engine and saw a 40 deg increase.

[kaa]

Thanks!

Yeah, I'm starting to think that the whole induction leak theory isn't that great. I'll do proper cruise checks.

Walt, are you saying that EI is 40 degrees lower steady state or that it's slower to react?

[Kent Ashton]

You can check a CHT sensor by putting it in a tin can with a candy thermometer and enough engine oil to cover them. Heat with a propane torch or heat gun and compare the EIS reading.
https://www.amazon.com/Chef-Craft-21.../dp/B00440D3OC

[vic syracuse]

You may have 2 separate problems. First, you do have leaking intake gaskets, as evidenced by the increase in EGT when pulling the throttle back. I noticed some of you even mentioned my article on that topic! So glad to hear it!

Second, do make sure the config is right on the probes. I have seen that mistake more than once, and it almost caused a panic.

Once the config is checked, then check for all of the typical cooling suspects, as mentioned in some of the other posts.

But do change the intake gaskets. They may not make a difference in cooling on climbout, because you are at full throttle, but will make a difference at idle and other power settings.

Vic

[lr172]

Originally Posted by kaa

I'm starting to question the intake leak theory though. Perhaps the EGTs rise when the throttle is closed enough for the idle circuit to kick in, and it seems to be adjusted too lean?

Your prerogative to discard all of our advice. The idle circuits flows constantly. It is not turned on or off, though it progressively flows more as vacuum increases (i.e. MAP drops), unlike the main jet that flows linearly with air flow volume.