Low oil temperature on 915iS.

fara

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It is not about Rotax engine, it is about Magni oil thermostat and position of the oil radiator below oil tank.
Pephaps if oil radiator on M-24 were above the oil tank, as on M-16, the water would accumulate not in oil radiator, but in the oil tank, from where you drain it every oil change and not even notice.

Oil radiators in almost all Rotax equipped aircraft will be below the oil tank and at best at the same level. That is not the problem. Oil is heavier than water and water should not accumulate at the bottom of the radiator but pass through the radiator as it will be at the top. Most of the Mocal or Permatax thermostats are for 185 deg F.
Every 100 hours Rotax requires that oil change is accompanied by taking all oil out, cleaning the oil tank inside and refilling the whole system with new oil.
Getting the oil temp to 212 F for a minute can and likely should be done after a flight on the ground by running up the engine stationary. If in cold weather, you can cover a part of the radiator for the winter if necessary. Making a system that works in the middle-east and in frozen places without overheating is not easy. The lowest common denominator wins. You'd rather run a little cooler than overheat an engine

Edit Add: duh oil floats on water usually. I have them backwards. But if the flow is correct and the oil radiator is made correctly there should not be accumulation of water at the bottom. It should flow through and then if you get the oil temp up to 212 for a couple of minutes that water should evaporate
 
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Tyger

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Oil is heavier than water
Are you sure about that??
A gallon of water is about eight pounds. Most motor oils are only about seven pounds per gallon.
Looking online, I see that 1 cubic centimeter of SAE 15W-40 is 0.87 grams. Water is, of course, about 1 gram per cc.
 
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Burrengyro

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Are you sure about that??
A gallon of water is about eight pounds. Most motor oils are only about seven pounds per gallon.
Looking online, I see that 1 cubic centimeter of SAE 15W-40 is 0.87 grams. Water is, of course, about 1 gram per cc.
Hi Tyger & Abid,
Potentially, water, residue and other "muck" could accumulate at the bottom of the oil radiator? Should we be draining the oil radiator, the oil reservoir and also the turbo oil sump to do a thorough oil change, followed by a full oil system purge? Would this be overkill? If we are only draining and cleaning the oil reservoir at 100 hours, is a full oil system air purge necessary?
I am stuck with covering a portion of the oil radiator to get the temp up to burn off any water vapour from the oil, especially during winter as I have no thermostatic valve. Looking forward to Inquiring Mind's tests on the new thermostatic valve system. An effective thermostatic valve could be very useful.
Many thanks, John H.
 

Tyger

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Hi John H,

I can imagine water accumulating in the low point of the system, but I would think proper oil pressure (actually suction, at the cooler) would keep all liquids moving pretty well through the cooler. Water is not that much more dense than the oil, which obviously needs to flow through there pretty freely.

In my case, the low point of my oil system is my oil tank. I have never seen any water in it, as I mentioned earlier in this thread. But the tank is exposed to the atmosphere, whereas an oil cooler cannot be.

My schedule for actually disassembling/cleaning the oil tank is every 200 hours. That's mostly to check for lead sludge if you use much 100LL. I only use 100LL when flying away from home (and then I add Decalin), so my oil tank has been quite clean each time I have checked it.
CLEANING THE OIL TANK
General note
This procedure is optional and requires purging of the oil system. See Chapter 12–20–00 section Purging the oil system. If using leaded fuel it is required to clean the tank every 200 flight hours. It is only necessary to clean the oil tank and the inner parts if there is heavy oil contamination.
(MML: 12-20-00, pg 49)


In my system, however, with the oil tank below the engine, it cannot be any more necessary to do a purge when removing the tank than when simply draining the oil during an oil change. In both situations both the IN and OUT oil lines are left dangling in air (perhaps if the tank is higher up such a purge might be necessary).
Where you do want to be quick to avoid having to purge, I think, is when changing the filter. Have the new one ready to go on as soon as the old one comes off. Same goes for the magnetic plug check.

I agree with most of what Abid just said; I think he's right that if you run it up a little once you have landed (not much air streaming past your cooler) it should get your oil temp up to a good enough level for dealing with water in the system. Remember that the minimum temperature for simply running the engine is only 50C, and that's mainly for proper pressure/viscosity.

T
 

fara

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Are you sure about that??
A gallon of water is about eight pounds. Most motor oils are only about seven pounds per gallon.
Looking online, I see that 1 cubic centimeter of SAE 15W-40 is 0.87 grams. Water is, of course, about 1 gram per cc.

May be not but I have never seen water accumulated at the bottom of an oil radiator in 350 aircraft with 91X I have been involved in, trikes, Apollo LSA, Searey, gyroplanes
Edit: Yes duh oil floats on water usually. I have them backwards. But if the flow is correct and the oil radiator is made correctly there should not be accumulation of water at the bottom. It should flow through and then if you get the oil temp up to 212 for a couple of minutes that water should evaporate
 
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Are you sure about that??
A gallon of water is about eight pounds. Most motor oils are only about seven pounds per gallon.
Looking online, I see that 1 cubic centimeter of SAE 15W-40 is 0.87 grams. Water is, of course, about 1 gram per cc.
This would, of course, be the reason that when an offshore drilling rig or a tanker ship produces an oil spill on the ocean, it sits at the surface and threatens the birds and the beaches until they surround it with floating booms for eventual clean-up. If heavier, the oil would sink to the sea floor and create entirely different problems.
 

fara

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Here is a US purpose made thermostat for 912/914
Its a bit more expensive

However, honestly Permacool and Mocal thermostats at $75 are very good as well and if you simply use a slight cover over your radiator they will get the job done even in very cold environments. Like I said, a manufacturer is designing for a very large range of operating weather temps and they have to service the lowest common denominator. In the 915iS the coolant temp is also very touchy. You run the oil too hot and it starts to match the coolant temp closely but ideally you want the coolant temp in the 180 to 210 F range in flight. Taking oil to 212 for the whole flight will not do good for your coolant temp. So 212 F is a number you want to get to just for a few minutes and its best done on the ground after each flight.
 

fara

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Here is a US purpose made thermostat for 912/914
Its a bit more expensive

However, honestly Permacool and Mocal thermostats at $75 are very good as well and if you simply use a slight cover over your radiator they will get the job done even in very cold environments. Like I said, a manufacturer is designing for a very large range of operating weather temps and they have to service the lowest common denominator. In the 915iS the coolant temp is also very touchy. You run the oil too hot and it starts to match the coolant temp closely but ideally you want the coolant temp in the 180 to 210 F range in flight. Taking oil to 212 for the whole flight will not do good for your coolant temp. So 212 F is a number you want to get to just for a few minutes and its best done on the ground after each flight.

This oil thermostat is likely not fit for 915iS because its openings are not large enough as 915iS uses AN10 size instead of AN8 like 912/914. So I would not recommend it for 915iS
 

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This oil thermostat is likely not fit for 915iS because its openings are not large enough as 915iS uses AN10 size instead of AN8 like 912/914. So I would not recommend it for 915iS
Hi Abid and Tyger, Thanks for the great info. A thermostatic oil valve may speed up the warmup time in a Rotax 914 turbo and help maintain a better operating temperature. But does it prolong the cool down time before shutting down the Rotax 914 in respect of ensuring the turbo is cooled enough to prevent coking of the oil in the turbo? Maybe I'm overthinking this? Thanks, John H.
 

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Oil is heavier than water and water should not accumulate at the bottom of the radiator but pass through the radiator as it will be at the top.
Are you sure? :)
Oil-water.jpg

P.S. I have not seen the post #42 of Tyger before posting that pic.
 
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Inquiring Mind

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Potentially, water, residue and other "muck" could accumulate at the bottom of the oil radiator?
It did in my gyro.

Should we be draining the oil radiator, the oil reservoir and also the turbo oil sump to do a thorough oil change, followed by a full oil system purge?
Not if you keep the oil at 100C or higher inflight.
 
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fara

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Hi Abid and Tyger, Thanks for the great info. A thermostatic oil valve may speed up the warmup time in a Rotax 914 turbo and help maintain a better operating temperature. But does it prolong the cool down time before shutting down the Rotax 914 in respect of ensuring the turbo is cooled enough to prevent coking of the oil in the turbo? Maybe I'm overthinking this? Thanks, John H.

you are overthinking it. But I would suggest anyone with a turbo idle about 5 minutes before shutting the engine down. I did see on one MTO Sport 2017 with 914 that the after muffler installed was so close to the turbo oil reservoir that it cooked that oil and the guy almost lost the engine and Rotax basically told him not their problem because after muffler is not a Rotax part nor their recommendation
 

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.

The impeller on the exhaust side of a turbo will glow red hot under load
The intake side remains relatively cool because of the large volume of intake air passing through it .
Both impellers are joined together on a common shaft with an oil-fed bearing between them.
Most turbos will last thousands of hours under load ... normally they will outlast the engine.

One of the main reasons an engine should be idled before shutdown is to let the red hot impeller cool down.
Otherwise the heat transfers through the shaft and over to the intake side.
This heat then damages the bearing and seals ... which were not designed to handle the heat.

The secondary reason to idle is because the engine oil pump keep feeding the center bearing
both for lubrication and cooling.

The turbine impellers continue to spin after the engine is shut down ... sometimes for several minutes .... if everything has slowed down and cooled down enough oil remains in the bearing so that no damage occurs.

I have worked with equipment operators who immediately shut down an engine when the coffee truck comes .... 10 minutes later you can still hear the whine of the spinning impellers .

Summary ... exhaust impeller heat is the enemy .... not so much the coolers or oil or oil lines..

.
EDIT to add .... my post is partly in response to Fara post 52 ... (He is correct)

.
 
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Burrengyro

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.

The impeller on the exhaust side of a turbo will glow red hot under load
The intake side remains relatively cool because of the large volume of intake air passing through it .
Both impellers are joined together on a common shaft with an oil-fed bearing between them.
Most turbos will last thousands of hours under load ... normally they will outlast the engine.

One of the main reasons an engine should be idled before shutdown is to let the red hot impeller cool down.
Otherwise the heat transfers through the shaft and over to the intake side.
This heat then damages the bearing and seals ... which were not designed to handle the heat.

The secondary reason to idle is because the engine oil pump keep feeding the center bearing
both for lubrication and cooling.

The turbine impellers continue to spin after the engine is shut down ... sometimes for several minutes .... if everything has slowed down and cooled down enough oil remains in the bearing so that no damage occurs.

I have worked with equipment operators who immediately shut down an engine when the coffee truck comes .... 10 minutes later you can still hear the whine of the spinning impellers .

Summary ... exhaust impeller heat is the enemy .... not so much the coolers or oil or oil lines..

.
EDIT to add .... my post is partly in response to Fara post 52 ... (He is correct)

.
Hi Martin W & Abid,
Thanks for the explanations and clarifications. Much appreciated. John H
 

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This heat then damages the bearing and seals ... which were not designed to handle the heat.
Just to note, the Rotax turbocharger does not have bearings or oil seals per se, but, rather steel bushings and steel rings that keep the oil in the central chamber of the turbo with the help of pressurized air.
The main problem with excess heat is the oil "coking". Preventing that is why it's a good idea to run oil through the turbo for a few minutes at idle speed before shutting down.

gives a pretty good description of how the Rotax turbocharger works internally.
 

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The main problem with excess heat is the oil "coking". Preventing that
Preventing (to the degree) an oil coking is very easy: use fully synthetic oil (Mobil 1 Racing 4T). That would require the use of unleaded gas, of course. Aeroshell Plus 4 - is semi-synthetic and thus more prone to oil coking. Been there...
 
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Tyger

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Unfortunately many folks don't have E0 unleaded available near them. And if you actually need to refuel at an airport, good luck finding one with mogas. If you use a semi-synthetic, you have options with the fuel; you just need to not abuse the turbo.
 

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Unfortunately many folks don't have E0 unleaded available near them. And if you actually need to refuel at an airport, good luck finding one with mogas. If you use a semi-synthetic, you have options with the fuel; you just need to not abuse the turbo.
Occasional use of 100LL is not a problem at all with fully synthetic oil. Just add Decalin to 100LL and change an oil more often.

 
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Tyger

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Yes, I always carry Decalin on cross countries. However Prof. Paul Shuch (LSA & Rotax guru*) claims the lead phosphate dust it creates and (mostly) ejects in the exhaust can cause problems with certain exhaust systems, particularly ones with flexible pipes. But he was using 100LL almost exclusively.
*http://avsport.org/webinars/videos/rotax_alive.mp4 (see minutes 73-76)
 
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Inquiring Mind

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"Make sure you remove and clean your oxygen sensor every 20 hours to remove these lead phosphate deposits when using Decalin RunUp."
 
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