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Oil Filler Cap On or Off for prolonged Pre-Heating

We keep our 1969 aerobatic E33c hangered in the cold northeast (about 70 miles north of NYC), and fly about every other week. Recently discovered and purchased a $24 Wemo plug (https://www.belkin.com/us/p/P-F7C063/) which allows us to remotely turn the Tanis pre-heater on our IO550 via the internet which has made a positive difference in how we can use the plane (not have to wait around 3 or 4 hours to properly heat the engine and oil).
Question is; what are the groups collective thoughts about leaving the oil filler cap open a little to allow moisture to escape during the pre-heating from the night earlier, and also what (if any) problems could come about from pre-heating, but then not flying after that due to weather etc?

Looking forward to hearing anyone's thoughts or experience on this matter

Thanks in advance.

Model: Bonanza E33C
Posted 1/11/2019 - 3 years ago
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Unlatch the oil filler cap after you land, lets the warm moist air escape from the crankcase thereby avoiding condensation, leave it up maybe an inch between flights. I live in NC and for the last several winters have left the preheat plugged in full time with cowlings closed and a thin blanket covering. No problems and the oil analysis reports come back clean. Just my experience.

Posted 1/11/2019 - 3 years ago
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Have you considered an engine dehumidifier?

Posted 1/11/2019 - 3 years ago
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Thanks Charles, we've always opened the oil filler cap after a flight, but then closed it again before leaving the hanger. Will try leaving it open a crack.

Never considered an engine dehumidifier William, but will look into that thanks,

Posted 1/14/2019 - 3 years ago
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In reply to: Charles B. Mirman, Esq | 1/11/2019 - 3 years ago

Unlatch the oil filler cap after you land, lets the warm moist air escape from the crankcase thereby avoiding condensation, leave it up maybe an inch between flights. I live in NC and for the last several winters have left the preheat plugged in full time with cowlings closed and a thin blanket covering. No problems and the oil analysis reports come back clean. Just my experience.

My practice also.

Posted 5/26/2019 - 3 years ago
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Jon,

In the winter, I plug in my engine heater, cover the engine cowl with a blanket. I leave it plugged in all the time I am not flying.

I do not open the oil filler, other than to check the oil level.

I do not have excess moisture in my engine or any corrosion.

In the winter I put a piece of cardboard in front of the oil cooler to keep my oil temp up (I fly LOP except when taking off and climbing). My oil temp, in the winter is rarely above 200 dF and never more than 220 dF.

Oh I do have an 1in x 2 inch opening in the cardboard which helps keep the temps down. Some folks put aluminum tape on the cooler, as recommended by Norm Colvin in his book.

Posted 5/27/2019 - 3 years ago
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I wrote the 24-hr Preheat article, and the follow up based on Tanis President's update.
The important thing seems to be to keep a warm top, and then 'yes', let the warm humid air escape.
I also made (might have been an ABS article) a PVC ring/collar with a red "Remove me" tail to be that 1" spacer.
Works great.

Posted 5/27/2019 - 3 years ago
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Oil Filler Cap On or Off for prolonged Pre-Heating