O-360 #2 and #4 high CHT

LeMar · #1 10-08-2017, 02:36 PM

Backround:
O-360A1A, 1,000 Hrs since new, RV-7, 1,000 Hrs
Never had high CHTs until about 50 hours ago when #2 and #4 became higher on climb out. Now, at 120 kts cht on those two cylinders climbs to 420 fast and would go higher if I didn't back off power.
Ignition: EFII on bottom plugs, slick mag on top

So far I've changed intake couplings and gaskets, checked the carb for looseness, changed mag and harness. Nothing has had any real effect. Baffle seals aren't perfect but are pretty good and I can't see much change from several years ago. Checked #2 cht probe in hot oil and it tracks with a digital cooking thermometer.

Something has changed but I don't know what. I've read through high CHT posts here on the forums but haven't seen any describing symptoms like this.

Ideas?

Thanks,

LeMar

mr.sun · #2 10-08-2017, 03:03 PM

Double Check timing

Bob Martin · #3 10-09-2017, 05:10 AM

You don't mention a primer system?
If you have one, check that too.
Also check that the primer ports and injector ports are there and not leaking too.

snopercod · #4 10-09-2017, 05:14 AM

Quote:

Originally Posted by mr.sun

Double Check timing

Why would timing only effect two cylinders, please?

John Myers · #5 10-09-2017, 06:28 AM

I would check one of the double duty coil packs on the ignition system. One dead coil pack would leave two cyl's only getting fire from the mag and the cht's on them would go up.

N941WR · #6 10-09-2017, 07:20 AM

Quote:

Originally Posted by John Myers

I would check one of the double duty coil packs on the ignition system. One dead coil pack would leave two cyl's only getting fire from the mag and the cht's on them would go up.

That would cause cylinder temps to drop, not rise, and then only if both ignitions stopped firing on those two cylinders.

Check you baffles, you might have a crack that is letting the cooling air out. Look around the corner of #4.

N363RV · #7 10-09-2017, 02:22 PM

I know the other guy mentioned chts... but maybe you should look at the exhaust temps.
Exhaust gas temps do go up when you run on only one mag or one side of a dual ignition system. You haven't mentioned your exhaust gas temps.
Did you change your aviation style plugs to new ones or at least confirm the gap? Don't forget to check the resistance too. 1k to 5k is acceptable.

I would also stick a light in the cowling at night and try to observe any egregious air leaks. That side of the cowling gets the least amount of air in it during a climb on a normal day... but 120kt should overcome even the worse leaks.

If the carb got some junk on one side it might alter the performance of the jet negatively.

I hope you get it worked out. Please post what the final resolution is.

Raymo · #8 10-09-2017, 02:49 PM

Is your oil cooler mounted on the back of #4 and did you remove a winterization plate about 50 hrs ago? (sorry to state the obvious).

LeMar · #9 10-10-2017, 11:12 AM

Some good ideas here. I think the next thing to check is CHT vs EGT as I don't remember what the EGTs were doing. Nothing that would have alarmed the system or me but still, maybe something is happening.
The other thought is to remove the primer lines from #2 and #4 and plug the holes. The primer system is the solenoid type and I never actually use it but rather use the accelerator pump for starting. Perhaps there is a leak on that side of the engine allowing air to be sucked in. I have checked for fuel leaks on the primer system but maybe air will leak in where fuel won't leak out. I'll post my findings.

LeMar

Bob Martin · #10 10-10-2017, 11:45 AM

Quote:

Originally Posted by LeMar

Some good ideas here. I think the next thing to check is CHT vs EGT as I don't remember what the EGTs were doing. Nothing that would have alarmed the system or me but still, maybe something is happening.
The other thought is to remove the primer lines from #2 and #4 and plug the holes. The primer system is the solenoid type and I never actually use it but rather use the accelerator pump for starting. Perhaps there is a leak on that side of the engine allowing air to be sucked in. I have checked for fuel leaks on the primer system but maybe air will leak in where fuel won't leak out. I'll post my findings.

LeMar

The solenoid has a "in" and "out"....marked with a 1 and 2....(not sure of the order), if it is reversed it can leak fuel though. The solenoid can go bad as well. The install manual says it can be mounted in any direction but recommended vertical, I think. All things to consider.
The above conditions usually contribute to rich running or stumbling at idle, not lean or higher CHT's....that most likely is a leak in the induction or primer line systems.
Bypassing for troubleshooting seems like a good idea.