Engine Dehydrator

[outermarker]

"I built an engine dehumidifier a few years ago using a Peltier cooler and aquarium pump."

My limited understanding of a Peltier is one side is cold, and the other side is heat...depending on the amount of current you push through it. In order to maintain 90 degrees engine/oil temp I would think you would have to have a pretty large power supply and amps of current? 

[Pinecone]

On 4/14/2025 at 9:52 AM, N201MKTurbo said:

The ideal condition for your engine is low moisture (dew point) and high temperature. I did a bit of research and humidity seems to be what drives corrosion not moisture content. So the perfect engine preserving machine will both remove moisture from the air and heat the engine. The engine could be heated by external heaters or pumping hot air into the engine. 

 

Hmm, sounds like what a basic standalone dehumidifier does.  Blow that air into the cowling and add some way to pump a bit into the engine and you get warm and dry.

[Pinecone]

18 hours ago, outermarker said:

"I built an engine dehumidifier a few years ago using a Peltier cooler and aquarium pump."

My limited understanding of a Peltier is one side is cold, and the other side is heat...depending on the amount of current you push through it. In order to maintain 90 degrees engine/oil temp I would think you would have to have a pretty large power supply and amps of current? 

He used to the cold side to remove the moisture from the air.  Not the hot side to hear the engine.

[DXB]

On 4/14/2025 at 9:52 AM, N201MKTurbo said:

The ideal condition for your engine is low moisture (dew point) and high temperature. I did a bit of research and humidity seems to be what drives corrosion not moisture content. So the perfect engine preserving machine will both remove moisture from the air and heat the engine. The engine could be heated by external heaters or pumping hot air into the engine. 

In areas with high humidity and warm temperatures, removing the moisture is your best bet. In cold places, or during the winter warming the engine will be more effective than removing moisture. 

Or you could move to Arizona. We do all that naturally.

I think it may be important to qualify the role of high temps. At a given relative humidity, higher temps will increase corrosion rate.  However, below about 40pct relative humidity, there is minimal corrosion irrespective of temperature.  In winter, heating the engine uniformly (both cylinders and sump) will drastically lower the RH as long as there's a path for moisture toe escape, so the increase in temp doesn't matter - this is a great strategy in cold parts of the country. Here the heat is a very effective dessicant.  (Think of your dry skin when running the heater at home in winter).  I'm not certain, but in wet humid parts of the country, running the engine heater in the summer may be less effective at keeping down RH, and in presence of high moisture the high temps may become counterproductive. A dehydrator may make more sense - it would be nice to see some data on this.  

On a related note, I'm pondering either the Black Max or the Drybot for summer use.  The cost delta is significant in favor of the Black Max, but I like that the Drybot can plug into either oil filler or the breather.  Any guidance from folks on pluses and minuses of these two options?

https://www.rpxtech.com/drybot.html

https://flyingsafer.com/2065

 

 

 

[Mooney-Shiner]

12 minutes ago, DXB said:

I think it may be important to qualify the role of high temps. At a given relative humidity, higher temps will increase corrosion rate.  However, below about 40pct relative humidity, there is minimal corrosion irrespective of temperature.  In winter, heating the engine uniformly (both cylinders and sump) will drastically lower the RH as long as there's a path for moisture toe escape, so the increase in temp doesn't matter - this is a great strategy in cold parts of the country. Here the heat is a very effective dessicant.  (Think of your dry skin when running the heater at home in winter).  I'm not certain, but in wet humid parts of the country, running the engine heater in the summer may be less effective at keeping down RH, and in presence of high moisture the high temps may become counterproductive. A dehydrator may make more sense - it would be nice to see some data on this.  

On a related note, I'm pondering either the Black Max or the Drybot for summer use.  The cost delta is significant in favor of the Black Max, but I like that the Drybot can plug into either oil filler or the breather.  Any guidance from folks on pluses and minuses of these two options?

https://www.rpxtech.com/drybot.html

https://flyingsafer.com/2065

 

 

 

Read my pirep on Black Max. Bottom line: build your own in a fraction of time /cost

[glenn reynolds]

I have been using the blackmax for a year and half.  I can add some operational observations:

1) my blackstone oil analysis has not shown a silver bullet success.  my iron corrosion levels are higher than blackstone would like, which is of course contrary to what I had hoped for.  I have ordered a humidity sensor to allow me to monitor the output of the blackmax to see if the machine is actually drying the air.  

2) my mooney ovation runs an io550 which has a combination oil filler and breather.  As the breather pipe under the cowling has an ice hole (vent hole in the breather pipe to preclude blockage in the event the breather outlet ices over) I was not able to insert the blackmax dryer tube via the breather tube.  The oil filler is the next logical location but has several considerations:  To use the oil filler the oil dipstick must be removed, this means there is an increased risk of the engine being run with the oil dipstick removed.  in an effort to reduce this risk, I have a firm policy that the dryer tube is inserted into the dipstick or the oil dipstick is inplace and I don't allow ANY deviation, distraction during preflight is a known evil.  I have a magnetic stand to hold the dipstick with a towel lined yogurt cup on the inside of the hanger door so the dipstick is on the door or in the engine, no other location.  I keep paper towel adjacent to clean the oil from the dehydrator tube and wipe the dipstick clean with. 

3) the top of the io550G engine oil filler is the normal oil cap diameter about an 1.5 inches HOWEVER, the breather vent connects to the sidewall of that opening so again this is not the place to have the foam plug of dehydrator tube inserted as I would be pumping air out the engine breather.  The oil dipstick hole is MUCH smaller and only about 5/8 inch in diameter.  The blackmax comes with two foam plug sizes to go on the end of the dryer tube, a large 1.5 inch and a small 5/8 foam plug.  I installed the small plug, used a step stool and flashlight and am able to insert the tube into the oil filler pipe.  with practice this can be done without the stool and flashlight but it takes practice as the opening is not tapered.  

4) after several months of use, I count myself as very lucky,  I was able to observe that part of my foam plug had come off and was left inside the oil filler pipe after I had extracted the tube!  this of course could have been a very significant issues to have a wad of foam roaming around the inside of the crankcase looking for an oil channel to clog!  I have subsequently ziptied below the foam plug so it can't come off.  I was able using a super long set of forcep pliers to extract the erant foam plug but this could be a real issue I call it to your attention as something that I take very seriously.  

[0TreeLemur]

19 hours ago, outermarker said:

"I built an engine dehumidifier a few years ago using a Peltier cooler and aquarium pump."

My limited understanding of a Peltier is one side is cold, and the other side is heat...depending on the amount of current you push through it. In order to maintain 90 degrees engine/oil temp I would think you would have to have a pretty large power supply and amps of current? 

Ambient air is pumped past fins on the cold side of the Peltier, condensing out water.  The ambient air has a dew point of 70F or more.  The unit outputs air with a dew point less than 50F.  That air with reduced water vapor content is then pumped into the engine.  Unless the engine cools to near 50 at night condensation won't occur.  In a place with dew points near 70, the nightly low won't get much lower than 70.  So the relative humidity in the engine stays at about 33%.

[Scottknoll]

I used the black max for about 4 years. I sent it back for service 3-4 times. Only way I knew it wasn’t working was occasionally a humidity sensor. I ended up buying a drybot about 9 months ago. The tube to insert dry air works a lot better. It is a 5/8 OD silicone tube, it slides right into the oil filler port below the tap off for the breather line. I can hear the oil gurgle and know it is pushing air past the oil into the crankcase. That was never the case with the Blackmax.

The drybot monitors its function and output. It is desiccant based and dries it as necessary. It’s not cheap but seems much more robust than the black max.

If making your own or using the Blackmax I’d recommend using 5/8 OD tubing for connecting to the engine. It makes a nice airtight fit down inside the filler port, past the breather tube. No worries of foam falling off. There’s also an orange dust cap that fits on top of the oil filler port, the tube passes through this dust cap.

Their website has pictures.

Only downside is I think it pushes oil up out of the oil pan and into the case itself. So when taking the drybot out, roughly a quart shows up about 15-20 min later. Oil reading seems about a quart low until this happens. The IO550 also hides a quart through the rest of the engine if it’s been flown recently. So it can show up to two quarts low until it all drains back into the pan.

I have a spare Blackmax if anyone wants to make an offer…