[alcladrv]

On my -7A with an ECI O-360 engine and a fixed pitch Sensenich prop, the #4 CHT typically runs 30F to 60F higher than the other 3 cylinders, which are within 10 degrees of each other. It's much higher even in a 200 - 300 fpm climb than in level flight. Lately, I've observed that the oil temp typically exceeds 200F in cruise flight between 7,000 and 9,000 feet. The oil cooler is mounted on the aft baffle wall behind the #4 cylinder. The baffling appears to be in good order with good gap sealing all around.

The engine has an impulse coupled magneto on the left firing the bottom plugs. On the right, a Lightspeed system fires the top plugs. The engine was new when the plane was completed 19 years ago and now has over 1900 hrs. on it. Compressions are all in the 70s.

The high #4 CHT has become more and more performance limiting over the past couple of years. In other words, after takeoff, I need to pull the power back to 2200 - 2300 rpm just to get #4 cylinder cool down to 400F or so. Then I push the power back up to continue the climb until the #4 CHT approaches 430F.

I just wondered if there is possibly a connection between the high #4 CHT and high oil temps because of the oil cooler location.
Any thoughts?

 

[blaplante]

Do you have a diverter plate on the front of #2?

 

[D-Dubya]

Well, logic would point to something having changed since it was good before and now it's not as good. When did this start? Was it right after an annual condition inspection or any ignition work? Could timing have been changed or some other modification performed? What is the #4 EGT doing when the #4 CHT goes higher? Is its EGT basically following the others? If so, you can likely rule out a lean related issue. If it's different, then you may have an induction tube leak. Is it a parallel valve or angle valve 360?