Rotax 9 oil cooler orientaton

[skippydiesel]

To Rotax 9 aficionados and other interested parties

 

Reference: "The oil tank must also be mounted in the correct position and within the set limitations of the Z & X axes on the engine (See Rotax installation manual Section 79-00-00 Page 20. https://www.rotax-owner.com/pdf/IM_912_Series_Ed3_R0.pdf.)"

 

The Rotax instructions, above, advise that the oil cooler should be mounted horizontally (in relation to the engine) & near vertical. The instructions go on to talk about air entrapment with the advise against having the in/out ports located below the oil cooler .

 

I have strayed from this advise & have my oil cooler mounted longitudinally with the in/out ports on the (aircraft) right side. The oil cooler is angled sharply up (probably 25 degrees), so the out port is well above the in.

 

I have no air entrapment concerns with my oil cooler installation - are there other potential problems that I have not considered?

[IBob]

Hi Skippy, I couldn't open your link, but was able to open Edition 3 here:

https://www.rotax-owner.com/pdf/IM_912_Series_Ed3_R0.pdf

 

So, Edition 2 said mount the oil cooler below the oil pump, but if that wasn't practical mount it above, but the cooler ports had to be on the top of the cooler, regardless. And the Edition 2 illustration showed that.

Edition 3, however, says the oil cooler must be mounted below the oil pump, no mention of mounting it above. (And the ports must be on top.) But the illustration still shows it both below and above: so I guess they forgot to alter the illustration.

 

Apart from that, I cannot see any other references to the orientation of the oil cooler.

 

So, provided it is mounted below the oil pump, and the oil cooler ports are on top, it looks as though you are complying with Ed 3 directions.

For greater clarity, I suggest you post a pic?

And you have some means of directing adequate cold air flow through the cooler in that location?

 

 

[Yenn]

mounted horizontally (in relation to the engine) What does this mean Skippy. Is it horizontal or not and what does it's orientation to the engine have to do with it?

It seems that people nowadays mix up horizontal with parallel.

[skippydiesel]

1 hour ago, Yenn said:

mounted horizontally (in relation to the engine) What does this mean Skippy. Is it horizontal or not and what does it's orientation to the engine have to do with it?

It seems that people nowadays mix up horizontal with parallel.

All true Yenn - if you open the Rotax Manual that I posted you will see what I mean. Essentially the cooler is to be mounted with its long axis in the same plain as the pistons (across the engine) with the in/out ports on top.

 

 

[skippydiesel]

5 hours ago, IBob said:

Hi Skippy, I couldn't open your link, but was able to open Edition 3 here:

https://www.rotax-owner.com/pdf/IM_912_Series_Ed3_R0.pdf

 

For greater clarity, I suggest you post a pic?

And you have some means of directing adequate cold air flow through the cooler in that location?

 

 

Don't know why that link would not open but as you have found out  this https://www.rotax-owner.com/pdf/IM_912_Series_Ed3_R0.pdfwill get you to the document & then search for the relevant page.

 

 

[IBob]

Skippy, maybe we are looking at different documents, but I can't see anywhere it says the cooler must be mounted in that orientation.

The only references I can see are on Page 22  of 79-00-00:

1. Mount the cooler below the oil pump.

2. Mount the cooler with the fittings upwards.

If I'm missing stuff here, I'm happy to be corrected........?

[skippydiesel]

1 hour ago, IBob said:

Skippy, maybe we are looking at different documents, but I can't see anywhere it says the cooler must be mounted in that orientation.

The only references I can see are on Page 22  of 79-00-00:

1. Mount the cooler below the oil pump.

2. Mount the cooler with the fittings upwards.

If I'm missing stuff here, I'm happy to be corrected........?

Seems to me that I have somehow read into the oil tank location/orientation the same info for the cooler - brain cells not getting ant sharper. Thanks for pointing out my error (had me worried for a while)

 

However I still have the cooler in/out lets at very different location to the Rotax sketch (ideal?) - I cant see why the in/out lets must be on top as long as I am confident (which I am) thet there is not air bubble trapped in my oil cooler.

[IBob]

Okay, saw your pics now.

I am certainly not any sort of engine or Rotax expert, but I cannot see any problems with the way you have it mounted.
 

I would think that the Rotax reference to having the ports on the top is to avoid anyone having them on the bottom, which would/could lead to varying amounts of air trapped, and the oil passing only through the lower part of the cooler, resulting in varying and inadequate cooling.

[IBob]

PS that really is a poor illustration on Page 20.
The description specifically states that the oil level must not be more than 400mm below the Z axis............but the picture shows the oil level (2) below that.

[BrendAn]

my oil cooler is on the side with a scoop feeding it air. my oil tank is behind the passenger seat with hoses around 2 mt long.

[skippydiesel]

4 hours ago, BrendAn said:

my oil cooler is on the side with a scoop feeding it air. my oil tank is behind the passenger seat with hoses around 2 mt long.

Wow!

[BrendAn]

12 minutes ago, skippydiesel said:

Wow!

its 20 yrs old so it must work ok.

[BrendAn]

That's where the oil cooler is. I will take a photo of the oil tank tomorrow.

 

Edited September 26, 2022 by BrendAn

[pluessy]

FYI, Tecnam (on the P92 Eaglet at least) is mounting the oil cooler up-side-down eg the oil cooler ports at the bottom. It takes a bit more priming after the 5-yearly hose change to remove all air from the suction line & oil cooler.

I always crank it with the top spark plugs removed until I have positive pressure for at least 10s.

[IBob]

6 hours ago, pluessy said:

FYI, Tecnam (on the P92 Eaglet at least) is mounting the oil cooler up-side-down eg the oil cooler ports at the bottom. It takes a bit more priming after the 5-yearly hose change to remove all air from the suction line & oil cooler.

I always crank it with the top spark plugs removed until I have positive pressure for at least 10s.

So it does!

I don't understand why the oil would not pass across the lower radiator cores and out the other side, without displacing air that may be in the upper cores? Unless there is something tricky inside the radiator, like internal riser pipes from the ports???

[pluessy]

If you have an air bubble in the top part of the cooler, there will be no heat transfer happening there. To flush this bubble out can be tricky. I haven't had any problems yet when changing the hoses but I don't run the engine unless I had good pressure while cranking with the plugs out. If there is a large volume of air flushed out while running, you could lose oil pressure while the engine is under load.

[IBob]

12 minutes ago, pluessy said:

If you have an air bubble in the top part of the cooler, there will be no heat transfer happening there. To flush this bubble out can be tricky. I haven't had any problems yet when changing the hoses but I don't run the engine unless I had good pressure while cranking with the plugs out. If there is a large volume of air flushed out while running, you could lose oil pressure while the engine is under load.

Yes. So I wonder if the radiator has internal riser pipes, so the oil is arriving and leaving at the top, even though the external ports are at the bottom.
I did a quick search, but was unable to come up with any part number or detail on the radiator they are using.

[Thruster88]

My guess is because there would be much more resistance to flow in a tube filled with oil than air that all the tubes in the cooler quickly fill with oil.

 

Worked on a foxbat recently with oil cooler ports on the bottom.  

[BrendAn]

13 hours ago, BrendAn said:

That's where the oil cooler is. I will take a photo of the oil tank tomorrow.

 

 

[Blueadventures]

5 hours ago, IBob said:

Yes. So I wonder if the radiator has internal riser pipes, so the oil is arriving and leaving at the top, even though the external ports are at the bottom.
I did a quick search, but was unable to come up with any part number or detail on the radiator they are using.

I've got an oil cooler from a mate who accidently cut it with a cut off grinder (yep, bugger.)  I wasn't there otherwise the oil cooler would not have been cut.  He got a new one from floods and the old one is still in my hangar.  I'll cut the end skin off and see how the pipping runs.  I'll post the findings.

[Thruster88]

Cut the end off and fit a lexan window on the suction end, apply suction and make a video showing the oil flow. It would be good to see what happens. 🤔

[Blueadventures]

43 minutes ago, Thruster88 said:

Cut the end off and fit a lexan window on the suction end, apply suction and make a video showing the oil flow. It would be good to see what happens. 🤔

Interesting idea / suggestion.  Will try that, have to glue up the cut area carefully so as to allow its uninterrupted original flow.

Edited September 27, 2022 by Blueadventures

[RFguy]

skippy, you might also note well this tidbit in the rotax install manual 

 

"
At higher positioning of the oil tank, oil might leak through clearances at bearings back
into crankcase. Oil tank will be empty and all oil will be in the crankcase. If fitted too low
it might happen that the oil filter will be drained. In that case oil pressure will be too low
for the first seconds after starting the engine."

 

[skippydiesel]

Thanks RFguy - have measured my oil level relative to crank case , as per Rotax installation instructions, and find everything to be well within listed parameters.