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  #11  
Old 12-07-2017, 03:11 PM
JBPILOT JBPILOT is offline
 
Join Date: Nov 2007
Location: Jesup, Iowa
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Default Yes - - -

Another design of mine. Many call it the "Bender Baffle". That is why I can fly comfortably, even at 4 degrees outside temp. Nice warm air comes from the rad. by forcing the temps up, and slowing the flow down. It also helps warm the entire engine.
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Flying RV-12 - Serial #120036
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  #12  
Old 12-07-2017, 05:12 PM
mwardle7 mwardle7 is offline
 
Join Date: Oct 2009
Location: Utah
Posts: 60
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Thanks for the input. I'm still confused though. If Rotax wants the temp sender on the oil pump, and specifies a recommended range of temperatures, why would you be comfortable flying below the recommended temp at the oil pump? You can get the water out of the tank, if the tank oil is hotter, and that is good. But aren't there other reasons why you would want the oil temp at the oil pump to be within Rotax specs? Does the temp affect the flow characteristics of the oil? If the oil is spec'd to be at a certain temperature before it enters the engine, there's gotta be a reason I would think. Thanks again for your patience with my questions!
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  #13  
Old 12-07-2017, 08:23 PM
JBPILOT JBPILOT is offline
 
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Location: Jesup, Iowa
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Default Will try - -

I don't believe Rotax needs the oil at the spec temp going into the engine, just need it to warm up at some point to stop moisture build up. They want the oil at 122F to take off at WOT, so 153 is fine in this cold air case. The Thermostasis is great for warm or cold weather warm up. The oil will certainly get cooled off by only slowly going thru the cooler, but it will still blend as needed to keep working well.

Also, adding this. I don't think Rotax ever planned on someone like me adding a thermostat into the system. They wrote the oil temp spec assuming it would all flow thru the cooler and not go thru what I designed. It works, and works very well.
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Last edited by JBPILOT : 12-07-2017 at 08:30 PM.
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  #14  
Old 12-08-2017, 07:45 AM
Mich48041 Mich48041 is offline
 
Join Date: Apr 2008
Location: Riley TWP MI
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It seems to me that if the oil-cooler-bypass thermostat is set at 190 degrees F and if the oil temperature sensor is located relatively close downstream of the thermostat, then the oil temperature should be 190 degrees or more. Since the oil temperature is only 153, then it seems that the thermostat is not working right. Why is the thermostat not opening to bypass the cooler? Or am I not understanding how it works?
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  #15  
Old 12-08-2017, 08:22 AM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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The thermostatic valves typically used on Rotax installations are unable to shut off all oil flow to the oil cooler. This is a safety feature to prevent the oil in the cooler circuit from ever getting super cooled and potentially becoming so viscous that it would restrict oil flow if temperatures rose and the cooling capability was needed during the flight. A Lycoming engine oil cooler circuit works the same way.
So if the residual flow is being cooled too much because the OAT is very cold, even the use of a thermostatic valve will never bring the temp up to the normal range.

The Rotax 912 operating manuals says....

Avoid operation below normal operation oil temperature
(90 to 110 įC / 194 to 230 įF)


This temp is what you see on the gauge. Not what you think the temp is reaching in the tank.

The oil cooler cover plates were developed to give operators a simple means of elevating the oil temp. In very cold conditions it may still not be possible to achieve the minimum recommended, but the closer you can get to that, the better.
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  #16  
Old 12-08-2017, 10:52 AM
JBPILOT JBPILOT is offline
 
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Default Joe - -

INITIAL NOTE : The Thermostasis unit is considered a 98% bypass. Not at all like the automotive designs which are considered 10% bypass.

The Therm forces oil to go thru the cooler when the desired temp is reached. Oil comes back from the cooler TO THE THERM and is blended with hot oil from the tank and sent to the engine. The tank oil can be 200, but the blended oil going back can be 153 as you saw on my display when it was VERY cold outside.

I understand this is a confusing issue. There should be a tank temp option which would help everyone understand how a Therm affects the flow and blending.
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  #17  
Old 12-08-2017, 11:08 AM
Mich48041 Mich48041 is offline
 
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I understand that thermostat bypasses between 90 and 98 percent of the oil around the cooler and up to 10 percent of the oil goes through the cooler. My RV-12 does not have an oil thermostat. I suspect that if 90 percent of the oil cooler were blocked off, then the oil temperature would be greater than 153 F, even if it were 0 F outside. But do I want to fly in those conditions to find out?
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  #18  
Old 12-08-2017, 11:23 AM
rvbuilder2002 rvbuilder2002 is offline
 
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I do understand how it works John (we actually have one installed on the RV-12iS).

The valve is plumbed into the system so that the oil pump pulls oil either directly from the oil tank (when the oil temp is cold) or from the oil tank through the oil cooler and directly from the tank, with this ratio controlled by the variable valve within the unit.

Depending on the actual oil temp, the thermostatic valve varies the amount of oil sent through the oil cooler but if the OAT is very cold it can not shut it off enough to keep the oil temp within the green as the photo of your oil temp indicates.

Bottom line.... if the valve where able fully control the oil flow through the oil cooler it would be able to deliver oil at the valve rating of 190 F. (or at 205 F if that unit were being used).
Since it doesn't, it doesn't matter what the ratio of bypass is (BTW I have never seen 98% published anywhere).

So it can mean only two things....

- Either that the engine isn't able to heat the oil enough to get it up to 190 because of the cold OAT... even if the oil cooler is barely doing any cooling

or

- There is still too much cooling taking place at the oil cooler even if the thermostatic valve is installed and doing the best it can to bypass the oil cooler.

My opinion is that it is the second one because if you partially block the oil cooler it raises the oil temperature.
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  #19  
Old 12-08-2017, 12:40 PM
JBPILOT JBPILOT is offline
 
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Default Scott - -

You likely do not get to, or want to, fly in very cold weather, but here is what happens. Even in cold weather the 98% bypass Thermostasis directs almost all oil thru therm back to engine, with almost none going thru the cooler. After initial start up if you watch the oil temp in warm or cold weather you will see the oil temp go up to approx. thermostat value, then it pauses, and quickly starts back down. That is when the therm closes and forces some of the oil to go thru the cooler, which is why the indicated temp goes down fast, but then stabilizes, until it determines the blend level needed to keep the tank temps at therm value. From then on, you are seeing the blended return temp. The colder the weather, the lower the temp you see on the display. The tank is still at therm value temp.

I would suggest you call Thermostasis and talk to the owner. I am sure I have it correct.
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  #20  
Old 12-08-2017, 01:32 PM
Aircraft Specialty Aircraft Specialty is offline
 
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Default

Quote:
Originally Posted by rvbuilder2002 View Post
I do understand how it works John (we actually have one installed on the RV-12iS).
Scott,

Thatís awesome news to hear. It appears that Vans has come to the conclusion that a thermostat is a very worthwhile addition to the rotax engines in cold weather climates.

We have been selling a complete thermostat install kit since March, 2014 for the 912ULS rv-12 Aircraft. Unfortunately SLSA builders have repeatedly been told that there is no data to support installing a thermostat. Since Vans now appears on board with the idea of the Thermostasis, letís work together to make it available for SLSA customers. We are already utilizing the same thermostat and have figured out the hose routing and lengths to fit into the cowl well. Also, there is detailed documentation for the installation.

It would be a great way to allow all the SLSA owners in cold climates the option of installing a thermostat.

Steve
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