Moisture in the engine compartment

Robin Hood

Robin Hood

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Jun 11, 2019
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Robin Hood
Hey guys wonder if you have any advice for me? I was out flying my Cessna 150 this evening. After flying I noticed what appeared to be condensation on the nose gear strut so I took a closer look and it was also covering most of the lower engine area. Just a light moisture coating... weird and I’ve never noticed it before. The weather conditions were lower 30’s OAT and 75% humidity so I flew with the carb heat on most of the flight which was about 40 minutes long. Is it possible that this is a condensation problem or does it sound fuel related? The smell and feel of the stuff is watery at best
 
When you say "lower engine area", I assume you actually mean the outside of the lower engine cowl?

Fuel (100 LL) will evaporate very quickly, and usually leave a blue stain. You probably have water condensation from the high relative humidity as the evening temps dropped.
 
Some inside the cowl below the carb/air intake also there was some blue streaking on the wheels pant which would collaborate with your comment on blue stain. And yes it was on the outside as well
 
Robin Hood said:
Some inside the cowl below the carb/air intake also there was some blue streaking on the wheels pant which would collaborate with your comment on blue stain. And yes it was on the outside as well
Click to expand...

Time to have a good look for a fuel leak then!
 
A fuel leak could cause condensation. As the fuel evaporates it absorbs heat, chilling everything it contacts. At high humidity you'd get condensation or, in your case, frost, since the temps were low enough to chill the cowl a little below ambient.
 
Did you happen to refuel and possibly prime before heading to your parking spot? Excess fuel will sometimes leak out from the carb air box and cause the inside of the cowl to be wet. I’ve also had moisture inside my cowling caused by a leaking fuel line in the 150. The fuel line that goes through the firewall to the gascolator had corroded and a pinhole leak developed. It caused moisture in the cowl and inside the aircraft on the copilot side behind the rudder pedals.
 
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