Went up yesterday with my CFII to get my BFR done, and had to cut things short because the engine was overheating. It's been running hot for its entire life (roughly 500 hours since being built), but not as hot as yesterday. The back 2 cylinders hit 460 degrees, and the oil temp red-lined--yet OAT was only about 82F. No problem with oil pressure.

It's fresh out of its annual--this was also the immediate post-maintenance flight, but the only major thing done this time was to R&R the prop after having it resealed. My IA had found that the timing was 3 degrees more advanced than the book calls for, so he'd put it spot on, but instead of it improving things, it was worse than usual.

This is an O-360 180hp Lycoming Avcon conversion in my P172D. The engine analyzer is an Insight G1. Fuel flow on take off exceeds 12 gph, but I don't usually watch it while I'm taking off--and usually I have the EI fuel flow meter set to fuel pressure during TO and landing. Typical climb fuel flow is around 11.5 gph, cruise is under 9.8.

Any thoughts?

Cary

Have you checked the vernotherm valve (controls flow to the oil cooler)???

Having good baffling that fits correctly is very important to proper cooling.

My guess would be baffling since you've had this problem for sometime. I would recheck the timing for sure, maybe get two different people to check it. Make sure even the smallest holes are plugged in the rear engine baffles.
Ron

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All suggestions so far are good ones to look for. How does it preform compared with others, of its kind, climb, speed and GPH?
1. I have been told that a week impulse coupling spring can cause the timing to retard as the RPM increases; this will cause overheating and poor performance. Does it have a loud CLACK when starting, or a week click?
2. Incorrect cam timing will also cause poor performance and poor fuel economy, (not uncommon on Franklins) and is something that gets by most techs. Overlap should be close to or dead on TDC.

I appreciate the comments. I've passed them onto my IA.

FWIW, the baffling was replaced last year and was all bent the correct direction. There certainly aren't any largish gaps anywhere.

Power and economy have always been good. My airplane typically out-climbs and cruises faster than most 180hp Skyhawks, although not by a lot. Cruise is around 9.8 gph.

I haven't had a chance to talk with my IA yet this week, but I will report the outcome of all this info, and what he does with it.

Cary

As B75 sugested, the vernotherm oil cooler control is in the lead. Good luck and keep us informed.

172heavy wrote:As B75 sugested, the vernotherm oil cooler control is in the lead. Good luck and keep us informed.

Almost forgot, Pacific Oil Cooler Service can test it.

Well, the overheating isn't totally cured, but it's a whole lot better--call it "overwarming". My IA has done a little baffle changing and plans to do more by adding a baffle in front to force more air into the upper part of the cowl, but the big thing was to reduce the timing from 25 BTDC to 20 BTDC, a suggestion of Mike Busch, the IA Guru who writes a lot of maintenance articles for various publications. He told me that Lycoming had changed the timing specs for the IO-360 from 25 to 20, and although they hadn't addressed the O-360, he thought it was worth a try.

I expected a noticeable loss of power by reducing the timing, but I couldn't tell any difference. Climb rate is probably the biggest indicator of available power, and that seemed totally normal. It was a hot day (96F on the ground), so DA was in the neighborhood of 8000'+. Both my BFR instructor and I are in the 200# range, plus I had my usual "stuff" in the baggage compartment, running 3/4 tanks, so let's call it moderately loaded.

My IA did not pull the vernatherm, but clearly it is opening, as the oil cooler is too hot to touch. Getting the CHTs down on the back 2 cylinders made quite a difference in the oil temp--again, still pretty warm, but not redlining, and easy enough to cool down by reducing power and either flying level or descending.

Of course, the best part was I was able to complete my BFR--yeah, I still know how to fly after being down since February for one reason or another.

Cary

Interesting fix, I would be interested in seeing if there is a performance difference or lack of, at altitude with the timing change.

The highest we flew a couple days ago was 7500' MSL, which on that day would be roughly 11,000' DA. From 9+ years and roughly 500 hours of experience with the airplane, it all seemed pretty normal.

Incidentally, we also checked fuel flow, which at full power on take off was 13.8 gph, and again during full power applications at altitude. Of course, there were some fluctuations up and down from that a couple of tenths--it is, after all, carbureted, and floats bounce. But that's well in the ball park of what it should be.

I want to express my appreciation for the ideas several have had, not only in this thread but in PMs which were sent to me.

Cary

Glad you got it running within acceptable parameters, Here is another one you might kick around, add a skirt to the bottom of your cowl.

It already has cowl flaps which hang down pretty low while open. They're pretty visible in this picture taken at Leadville a few years ago.



Cary