Old Airplane Smells

[Ryan Smith]

Since getting my private, I have been flying my family's (ex) 170 quite a bit...averaging about 10 hours per month. Most of this time is coming from cross country time where the current owner of the airplane allows me to chauffeur her to give check rides so that I may build up my XC time for my instrument and commercial ratings. The airplane is a stock 1952 B model with the original C-145-2H engine, original cabin heater manifold, and original Hanlon-Wilson mufflers.

For as long as I can remember, immediately upon transition to cruise flight when the RPM climbs up to 2,500; a distinct odor of hot oil is detected, but subsides after about 10 seconds or so...or at least I think it does. I don't smell it after that period of time. It doesn't matter the time of year, if I'm only climbing to pattern altitude or today when I was climbing to 6,500 feet on my return trip back home, always within a few seconds of leveling off and coincident with the rise in RPM I smell hot oil. Is this normal, or is this simply unique to our airplane? It's done it for as long as I can remember...I don't recall it much prior to the overhaul in 1997 simply because I was a toddler when I would have flown in the airplane.

The smell has been nothing more than a curiosity of mine, and it's not just me that notices it. My wife has and was initially very concerned, but after I told her it has always done it, she took it at face value and nothing else has come up about it.

The only difference was today during my decent back into my home airport. My letdown typically consists of pulling the throttle back to between 2,200 and 2,300 RPM from cruise power to initiate a 500 fpm decent while maintaining cruise airspeed. Passing through 3,500 flying due west into the sun, I detected the odor of hot oil, but this time it was accompanied by some thin white smoke from near my feet. I quickly shut off the cabin heater and the smell subsided in its normal time period and subsequent opening of the cabin heater did not yield any more smoke. I decided to resume the flight to our home airport and landed without incident. The cabin heater had been open the entire flight, and during my initial level-off and cruise transition when the oil smell became prevalent, no smoke was noted. This was the first time I have seen smoke in conjunction with this smell, and the first time I can recall smelling it twice in a flight - even if I am doing pattern work - and the first time I smelled hot oil during any other phase of flight other than the initial RPM ramp in the transition to cruise.

I'm not worried about it, but I am curious. That said, I will be worried about it if need be. I plan to install a CO Guardian detector in the airplane once we buy it, but should I grab a stick-on CO detector to see what's going on? I've flown the airplane for extended periods of time and have noted no problems with CO poisoning, and the mufflers, though original, are in great shape and as of the last annual inspection in March, there were no cracks in the mufflers. I feel that this is a completely separate issue from muffler damage/possible CO leak.

Thoughts?

[Ryan Smith]

Ten points to Doug Mueller. I've got a list of things to investigate tomorrow.

[lowNslow]

Besides checking for a exhaust leak (i.e. hole in muffler) that is allowing exhaust to enter thru the cabin heat also check the door seals and landing gear external inspection cover seal. As you can see from this picture the flow from the exhaust stack goes right over these areas.

[hilltop170]

Wow! That plane needs some WashWaxAll Belly Wash!

[blueldr]

Break out a roll of duct tape for temporary sealing covers of the landing gear exit and any other openings in the exhaust flow stream. Then fly it again to see if that may be your problem.

[canav8]

Besides checking for a exhaust leak (i.e. hole in muffler) that is allowing exhaust to enter thru the cabin heat also check the door seals and landing gear external inspection cover seal. As you can see from this picture the flow from the exhaust stack goes right over these areas.

Great pic Karl, that is exactly what I told Ryan off line. D

[wingnut]

Ryan,
You wrote............." My wife has and was initially very concerned, but after I told her it has always done it, she took it at face value and nothing else has come up about it."
You either have a real peach, or need a CO detector.