Rotax Parts Supply Problems

[fallowdeer]

Mate put one of these on his Savannah. Reckons it works a treat.

[danny_galaga]

Since his oil is generally running too hot, I can't see that could do anything but run it slightly hotter at best.

 

But, it looks handy for my plane so thanks for the heads up 😀

[RFguy]

skippy said : "200%  agree!!! Air flow/cooling is , for those without a wind tunnel and all sorts of sensors, a dark art."

Skippy how can you 200% agree on something ?
Surely this means you never properly measured your agreement correctly in the past if this is a 200% agreement ?

Edited June 21, 2023 by RFguy

[skippydiesel]

GREAT NEWS!

 

B Flood can now supply the Rotax Extra Large Oil Radiator 886107.

 

It would seem their staffing levels have risen by 100%,  there are now 2 people working there.

 

My thanks to one & all for all of your constructive suggestions.

 

I will now have to work out where I can locate the oil cooler for best effect. I may end up with a cowling like this one;

 

 

[danny_galaga]

That cowling looks the goods. Have you contacted that owner to see what they've done, and how successful and also to get some drawings?

[skippydiesel]

3 hours ago, danny_galaga said:

That cowling looks the goods. Have you contacted that owner to see what they've done, and how successful and also to get some drawings?

I have tried to make contact - so far no luck

[skippydiesel]

Good News!

 

The changes I have made to the cooling system seem to be doing the job 🤣

 

Put the girl back in the air Sunday week ago for a 60 minute test - 30 +C on ground 22C @ 6500 ft Oil temp 105C on Climb Out & 97C in Cruise, Cylinder Heads (coolant) 85 C.

 

Since then have done a 2.4 hr in similar ambient temps - same result - delighted.

 

I guess the next problem will be winter overcooling. I have plans to address this, using the Cowl Flap (CF), currently removed (Linear actuator; faulty). My idea is to modify the CF  so that it will act  as a movable restrictor (hopefully speed up) the exit air.

 

Changes are:

• Coolant Radiator - Has moved from bottom of firewall, exposed to/restricting  ALL cowling exit air, to a forward position under gear box/front exhaust pipes. Now fed by ambient air temperature (fresh) nose air scoop. At this point no special sealing/ducting around radiator.
• Oil Cooler - replaced  Rotax Large, located under gear box , supplied with ambient air and separate ducted in/out air circuit,  with Extra Large cooler that has been located in the cowling exit air stream - no sealing/ducting.
• Cowling - Installed a forward air scoop.

 

 

 

Edited December 19, 2023 by skippydiesel

[RFguy]

Skip, in my opinion, that oil is still  too hot.  by about 10 deg C.... 

but, getting there.  water temps seems OK, something is wrong with your oil cooling... or biased too much one way., IMO.

[skippydiesel]

1 hour ago, RFguy said:

Skip, in my opinion, that oil is still  too hot.  by about 10 deg C.... 

but, getting there.  water temps seems OK, something is wrong with your oil cooling... or biased too much one way., IMO.

I beg to disagree - 

 

10 C degrees lower would make Climb Out 95 C - far too low.

Cruise would be around 84-87 C  this would be fine, although I would prefer a nice neat 90 C

For these relativly unsophisticated engine installations, it all about acceptable compromise. 

 

• Rotax recommend to get the oil temp above 100 C for a sustained period (?) at least once in an operating day.  For most aircraft this will occur during climb out. This is to drive off contaminates (H2O, fuel and combustion residues) in the oil.  If the oil is below 100C it will take longer to drive off the contaminants and some may not reach a sufficient temperature to be removed at all.
• The oil is a multigrade, designed to have the lubricant characteristics of a thin oil when cold and a thicker oil when hot. Mid 90 C is a three bears engine temp, neither too hot or too cold, just right - the oil should be operating  well within its designed operating range. I would expect a few degrees cooler in winter.

 

Remember; Rotax allow oil temps to Max 130 C  &  optimum to 105 C

 

I would like to see my coolant (CHT's) at or close to the current oil temperature (90-95C would be nice), as I suspect that in winter, the temperature will be much lower than my comfort zone. Similar oil/lubricant temps plays to my comfort and may reduce any potentially negative impacts from differing internal temperatures. I can adjust my coolant temp down by installing sealings baffles & up by some careful blocking of fin area or as mentioned having a modified cowl flap, that will restrict winter air flow to the whole cowling .

[Thruster88]

A cowl flap is the go for maximum speed.

I seem to recall some of us said the original cooling system would not be successful.  

[skippydiesel]

Skip, in my opinion, that oil is still  too hot.  by about 10 deg C.... 

but, getting there.  water temps seems OK, something is wrong with your oil cooling... or biased too much one way., IMO.

 

I beg to disagree - 

 

10 C degrees lower would make Climb Out 95 C - far too low.

Cruise would be around 84-87 C  this would be fine, although I would prefer a nice neat 90 C

For these relativly unsophisticated engine installations, it all about acceptable compromise. 

 

• Rotax recommend to get the oil temp above 100 C for a sustained period (?) at least once in an operating day.  For most aircraft this will occur during climb out. This is to drive off contaminates (H2O, fuel and combustion residues) in the oil.  If the oil is below 100C it will take longer to drive off the contaminants and some may not reach a sufficient temperature to be removed at all.
• The oil is a multigrade, designed to have the lubricant characteristics of a thin oil when cold and a thicker oil when hot. Mid 90 C is a three bears engine temp, neither too hot or too cold, just right - the oil should be operating  well within its designed operating range. I would expect a few degrees cooler in winter.

 

I would like to see my coolant (CHT's) at or close to the current oil temperature (90-95C would be nice), as I suspect that in winter, the temperature will be much lower than my comfort zone. Similar oil/lubricant temps plays to my comfort & possible that of the engine by reducing any potentially negative impacts from differing internal temperatures. I can adjust my coolant temp down, by installing sealing baffles & up, by some careful blocking of fin area or as mentioned, having a modified cowl flap, that will restrict winter air flow to the whole cowling .

 

My last 912ULS had, in Cruise, mid 90C for both oil /coolant &  105-110C in Climb Out (depending on OAT & load) - ran like the proverbial sewing machine and hopefully will continue to do so for its new owner. 

 

 Rotax Operators Manual:

 

"Oil temperature Oil temperature Max. 130 °C  Min. 50 °C normal operating temperature approx. 90 to 110 °C " 

 

"Coolant temperature: (coolant exit temperature) Max. 120 °C  Cylinder head temperature: Max. 150 °C "

 

"Avoid operation below normal oil temperature (90 to 110 °C ), as possible formation of condensation water in the lubrication system badly influences the oil quality. To evaporate possibly accumulated condensation water, at least once a day 100 °C  oil temperature must be reached"

 

Note: I have removed references to Fahrenheit equivalent temps 

Edited December 19, 2023 by skippydiesel

[skippydiesel]

24 minutes ago, Thruster88 said:

A cowl flap is the go for maximum speed.

I seem to recall some of us said the original cooling system would not be successful.  

True! It was worth giving the original builder a go - the workmanship was outstanding even if the concept was flawed - all wiser after the fact.

[RFguy]

that's all crap about oil having to be 100deg C. water doesnt suddenly start vapourizing at 100C.

rapid evap is well and truly underway at 80 deg C.  It does take a little more to evap water out of suspension/solution but not that much. Atmo pressure also falls with altitude, makes evap water easier...

[skippydiesel]

1 hour ago, RFguy said:

that's all crap about oil having to be 100deg C. water doesnt suddenly start vapourizing at 100C.

rapid evap is well and truly underway at 80 deg C.  It does take a little more to evap water out of suspension/solution but not that much. Atmo pressure also falls with altitude, makes evap water easier...

If I remember correctly from my Ag Science training (a squilian years ago) - it's not just water, it is other volatile  contaminants as well (mentioned earlier).

 

I would speculate, that water in an oil emulsion, may be a bit more resistant to evap/boiling off and as the Rotax advice is: "Oil temperature Max. 130 °C  Min. 50 °C normal operating temperature approx. 90 to 110 °C " - "and "at least once a day 100 °C  oil temperature must be reached" I can't see any down side to following their recommendations on this matter.

[RFguy]

My Kluger.. on my OBD in hot summer, never seen the oil go higher than 90 deg C. 

and i have never seen my Lycoming above 85C, sits a round 80-82C 

But, yeah I agree 90C-110C is probably fine, my point is that you are leaving some cooling on the table - that oil cooling is the low hanging fruit  to cool stuff in your engine. 

 

[BrendAn]

my man truck runs 127 degree oil temp all day.

 

[skippydiesel]

2 hours ago, RFguy said:

My Kluger.. on my OBD in hot summer, never seen the oil go higher than 90 deg C. 

and i have never seen my Lycoming above 85C, sits a round 80-82C 

But, yeah I agree 90C-110C is probably fine, my point is that you are leaving some cooling on the table - that oil cooling is the low hanging fruit  to cool stuff in your engine. 

 

I may try to raise the coolant temperature a bit, so that there is less of a gap between it and the oil temp.

"Coolant temperature: (coolant exit temperature) Max. 120 °C  Cylinder head temperature: Max. 150 °C "

The problem is, the only coolant measurement I have is CHT (in Rotax this is cylinder head coolant temp). I don't have coolant exit temperature - I presume this is as it comes out of the Radiator. There is no minimum temp or preferred range mentioned (stand to be corrected). The CHTof 85C seems a tad low.

Edited December 19, 2023 by skippydiesel

[RFguy]

Sounds like you need to change the balance of oil cooler airflow and coolant airflow. Skip what size ID hoses did you end up running between tank and oil cooler and engine ?

I'd keep the coolant below 110C, despite being an anti boil mix. rates of corrosion increase at higher temperatures. 

If you can measure coolant rise across the radiator or across the engine, that will give you lots of extra info. 

[aro]

10 hours ago, skippydiesel said:

"Coolant temperature: (coolant exit temperature) Max. 120 °C  Cylinder head temperature: Max. 150 °C "

The problem is, the only coolant measurement I have is CHT (in Rotax this is cylinder head coolant temp). I don't have coolant exit temperature - I presume this is as it comes out of the Radiator.

Coolant exit temperature is as it comes out of the engine i.e the maximum coolant temperature reached. It is to ensure the coolant isn't boiling in the engine.

CHT max is 150C for the 80HP but only 135C for the 100HP. My understanding is that this is for detonation margin with the higher compression.

[skippydiesel]

2 hours ago, RFguy said:

Sounds like you need to change the balance of oil cooler airflow and coolant airflow. Skip what size ID hoses did you end up running between tank and oil cooler and engine ?

I'd keep the coolant below 110C, despite being an anti boil mix. rates of corrosion increase at higher temperatures. 

If you can measure coolant rise across the radiator or across the engine, that will give you lots of extra info. 

Oil Hose ID -  Gates 8 GTH (GTH-8) ID  12.7 mm

[facthunter]

The temperature of the coolant  exiting the head won't give you the head temp. It will always be less and there can be  local hot spots as well. It will  tell you there's coolant in the system. (sort of) Nev

[skippydiesel]

7 hours ago, aro said:

Coolant exit temperature is as it comes out of the engine i.e the maximum coolant temperature reached. It is to ensure the coolant isn't boiling in the engine.

CHT max is 150C for the 80HP but only 135C for the 100HP. My understanding is that this is for detonation margin with the higher compression.

Hmmm!! - doesn't sound quite right to me.

• The CHT is head coolant temperature.
• Only the head(s) are liquid cooled.
• Ergo the highest temperature is surely the CHT. Max. 135 °C Coolant exit temperature Max 120 °C  - must be taken/sensed at a cooler point in the system.

 

I will refer this question to the Rotax Owners Forum for their comment.

 

ROTAX OPERATORS MANUAL

"2.2) Operating limits (912 S/ULS)"

"Coolant temperature: (coolant exit temperature) Max. 120 °C (248 °F) Cylinder head temperature Max. 135 °C (275 °F)"

 

 

 

[skippydiesel]

1 hour ago, facthunter said:

The temperature of the coolant  exiting the head won't give you the head temp. It will always be less and there can be  local hot spots as well. It will  tell you there's coolant in the system. (sort of) Nev

I do not disagree with your logic HOWEVER Rotax (in their wisdom) decided, many years ago, to change from metal CHT sensing , to coolant CHT sensing. They have continued to refer to the resultant  readings as CHT.

To the best of my knowledge all Rotax drivers have accepted this change, without too much concern ie it has become a convention.

Furthermore - most Rotax 912 installations only display the CHT, although I have seen the occasional sensor/readout plumbed into the (I think) water pump exit hose, using a T fitting.

As I am sure you will understand, adding another two joins in the hose, plus a sensor increases complexity/potential failure points/weight and unless the information received is going to significantly assist the pilot, in managing the engine, it's a wasted exercise.

[aro]

1 hour ago, skippydiesel said:

I do not disagree with your logic HOWEVER Rotax (in their wisdom) decided, many years ago, to change from metal CHT sensing , to coolant CHT sensing. They have continued to refer to the resultant  readings as CHT.

You are correct that the cylinder heads were changed to read coolant temperature not CHT. But Rotax do refer to this as coolant temperature, not CHT. If you are measuring coolant temperature the limit is 120C. Aircraft builders/manufacturers may or may not have made the change correctly.

 

The history as I recall:

 

• Originally, the sensors measured CHT and the limits were 150C for 912 and 135C for 912S. This was a bit hot for the coolant (particularly 150C), and coolant could boil in the heads, which was bad because a layer of vapor prevented proper cooling so it got even hotter and you had a vicious circle i.e. normal behaviour when a water cooled engine overheats.
• Rotax recommended waterless coolant which didn't boil at normal operating temperatures
• Unfortunately, the waterless coolant had less cooling capacity so engines ran hotter
• Rotax changed their recommendation back to conventional coolant, but required either measuring coolant exit temperature as it exits the engine, or change the CHT limit to 120C.
• Rotax introduced new heads which measure the coolant temperature, with a coolant temperature limit of 120C.

So the operators manual now lists CHT limits for engines with the old style heads (135C/150C CHT and 120C coolant), and coolant temperature limits for engines with the new heads (120C).

 

So you need to figure out which heads you have and what you are measuring to know which limits apply.

[skippydiesel]

ARO my friend,  I know which Rotax 912 ULS I have and I also know that Rotax still refers to the head temperature (now liquid/coolant) as CHT or "Coolant temperature limit measured in the cylinder head Engine types" see quote below and previous:

 

ROTAX OPERATORS MANUAL

 

"2.1) Operating limits (912 A/F/UL)" 

"Applicable for engine S/N without Suffix -01.....Coolant temperature: (coolant exit temperature) Max. 120 °C (248 °F) Cylinder head temperature Max. 150 °C (302 °F)"

"2.2) Operating limits (912 S/ULS)"

"Applicable for engine S/N without Suffix -01. Coolant temperature: (coolant exit temperature) Max. 120 °C (248 °F) Cylinder head temperature Max. 135 °C (275 °F)"

"Applicable for engine S/N with Suffix -01. .........Coolant temperature limit measured in the cylinder head Engine type Max. 120 °C (248 °F) 912 A/F/UL"

 

All of the above are, by convention, verbally & on your instrument panel, referred to as CHT.

 

Further - these are MAX temps - not to be exceeded. They are not normal running temps. So to some extent academic, as long as your engine is performing as expected, with Cruise coolant temps likely well below 100C .