D120 Oil Temp Bar Split?

[tevbax]

Co owner found this today after runup. Usually the bar is completely green after the oil warms up past 124. Any ideas?

The sender has been a bit erratic on temp, jumping high and low then returning to the 170 range. It’s most likely a loose connection somewhere.

 

[Tom Baker]

Oil temp will have that split until you get past 190°, then it will fill in with all green. Rotax says to get the oil temperature above 190° for each flight to help remove moisture from the oil.

[Anticept]

It turns completely green when you hit around 190.

It's to indicate if you have reached proper oil temp to drive out moisture from the oil in normal operation. If it's still black when you land and that keeps happening, your engine won't be happy.

[tevbax]

Got it, thanks guys! I've never noticed this before, but the logic makes perfect sense. 

[FredG]

I find all this a bit puzzling.  The vapor in the crankcase of every internal combustion engine is saturated with water, no matter the operating temperature.  Once the engine cools, that vapor will condense into liquid water and end up in the oil.  There is no doubt that the hotter the oil, the less water it will retain while the engine is running.  But, once the engine stops, it has water in it.

[Anticept]

The source of the water firstly is the combustion process. It's actually pretty crazy, you get somewhere around 30-40% of water from burning a gallon of gasoline! Most goes out the exhaust, but some blows by the piston rings.

The oil does have additives to help protect against small quantities of water and keep it in suspension. If it doesn't get hot enough, then with enough cycles, the water will begin to overwhelm the oil lubricating and protective properties as the water condenses and collects.

Water vapor takes up a huge amount of space (1600 times the space of water at the equivalent temperature), so when its vaporized, most is pushed out of the breather tube. What's left is extremely insignificant.

We're not really aiming for precision when we explain these things, simply because it's too complicated an answer for the question, and the specifics of which usually aren't covered in maintenance technician courses. We just get explained to us the end result of why in general terms

[Jim Meade]

It begins to sound like an old wives tale.  I wonder if George Braley has ever looked into this.

[Anticept]

It also could be a carry over from older days with old oils. Some oils sludge up when they get too much water in them.

You can also have a bit of fun with this: take out a little oil from your aircraft, and in a cup, see how much water you can add before it turns milky.

Then put it over heat. 180 degrees is actually the target temperature, 190 is the extra-conservative number. See how fast the water leaves the oil.

Then try again with it in a chamber (heat the entire chamber, the entire engine block is hot not just the oil). See how much water collects and condenses after sufficient time and compare to what you started with.

Mind you, in the engine the oil is being slung around like a bottled hurricane, so heating a puddle isn't quite the same for the experiment, but that's the gist of it.

[FredG]

Corey, yes, the main products of hydrocarbons (eg, gasoline) combustion are CO2 and H2O.  That is my whole point.  And, it doesn't matter a whole lot how quickly water is evaporated from 180 degree F or 190 degree F oil, once the engine stops running, there is plenty of water in the crankcase to replace it.  There is no eliminating water from the inside of the engine no matter how hot you get the oil.  

[ctbob]

I fixed an erratic, jumpy, temp problem by cleaning the sensor contact and wire and using RTV silicone to anchor it.  No problems since.

[Anticept]

19 hours ago, FredG said:

Corey, yes, the main products of hydrocarbons (eg, gasoline) combustion are CO2 and H2O.  That is my whole point.  And, it doesn't matter a whole lot how quickly water is evaporated from 180 degree F or 190 degree F oil, once the engine stops running, there is plenty of water in the crankcase to replace it.  There is no eliminating water from the inside of the engine no matter how hot you get the oil.  

 

The quantity matters a lot however, which is the entire point of encouraging people to get the oil warm. It would be absolutely silly to ignore the fact that there is a constant supply of water vapor from blowby. It's not about trying to make the oil absolutely water free, but rather to keep the water at low, manageable levels so that the engine oil can still perform what it was designed to do. There isn't much water vapor (relative to oil) inside of fhe engine anyways when it's all working correctly.

Cold oil would just rapidly cool the blowby, collect the condensate, retain most of it, and eventually turn the oil to a milky sludgy mess. Getting the oil temp elevated helps drive the water back out as well as keeping it from capturing more.

So coming back around to what you said, imagine someone does a lot of ground runs with good intentions for an airplane that isn't going to fly for a couple years, but they want to exercise it anyways.

They start it but don't let it warm up much. So when they stop it, that water vapor condenses and enters the oil. They do this twice a month every month. Everytime they start it and short run it, they get more water in the oil without much being driven out.

The inside of the engine is going to look like trash.

Now the other factor here is that 190 degrees isn't a done deal if there's already a lot of water in it. It still takes time for moisture to leave the oil. The theory is though if you're hitting 190 on each flight at some point, it goes back to keeping it manageable.

I hope that makes sense.

[CTSW Bob]

8 hours ago, ctbob said:

I fixed an erratic, jumpy, temp problem by cleaning the sensor contact and wire and using RTV silicone to anchor it.  No problems since.

Interesting…. My oil temp gauge is flawless on the ground then goes bonkers in the air.   I replaced the terminal connection, the sensor, the wire (single wire sensor), and even added a new ground wire and used a single point ground from the avionics to the engine with no luck.  Could it be as simple as a squirt of silicone?  I will give this a try.

Thanks for the tip CTBob, from another Bob

 

[ctbob]

Mine jumped around widely and being new to the aircraft at the time had me heading back to home shortly after takeoff.  I wasn’t particularly happy because I had to spend $6 for 0.0003cents worth of sealant to fix it , but it’s held for more than ten years.

[CTSW Bob]

Well, the cheap fix did not work.  Back to square one.  It has never been right once in the air, and likely will never be right.  

[GlennM]

Ground your Dynon case, not the rack, but the case.

[CTSW Bob]

Did that too.  No joy.