High oil temp on 912UL

by Gordon Grant in 912 / 914 Technical Questions 8 years ago

I am really struggling to find the cause of my 912 UL high oil temperature. On a relatively cool day (19C) it reaches 130C before I have reached 2000ft. Reducing power, levelling off and cruising for 10-15 mins eventually gets the temp down to just under 120C. A gentle climb at 90Kts and 200fpm will get me up to 2500ft but the oil temp goes back up to 130C. Eventually cruising at 100Kts with the pitch set for 4800RPM the temp will come down to 115C but no further. CHTs are also on the high side but stabilise at about 105C in the cruise.

So far I have done the following:
1. Installed a new Oil temp sender - no change;
2. Swapped the Oil and CHT gauges - same figures as before;
3. Checked the oil and water radiator matrix were not blocked;
4. Replaced all oil lines and firesleeve;
5. Removed and cleaned the oil tank - no sludge found;
6. Replace oil filter with new Rotax unit;
7. Filled with Aeroshell Sport Plus oil;
8. Conducted full oil system purge in accordance Rotax procedure (with thanks to Roger and others!)

My aircraft is a Europa Classic TriGear, 912UL and Airmaster Prop. These early Europas with the oil cooler located behind the left hand radiator are not fantastic when it comes to cooling, but I have never had this problem before. Yes it would get hot in the climb but getting to 2500ft was not a problem and a few minutes cruise would bring the oil down to 100C and CHT to 90C.

I have not changed anything and the engine starts and performs well. I am at my wits end as i am clean out of ideas and my aircraft is not really useable.

Help! All suggestions gratefully accepted.

Gordon Grant

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Re: High oil temp on 912UL

by Roger Lee » 8 years ago

Roger Lee

127 5.2k 4.78k

"pitch set for 4800 RPM" Do you mean you have it throttled back to 4800 rpm or the pitch of the prop is actually that course? What rpm do you see in climb?

I almost never see an Air master prop, but isn't that in flight adjustable? How many hours on the engine?

If you are over pitched with the prop the engine will run hot. If the engine rpm can achieve around 5600 rpm in level flight and then you throttle back then it's not an issue. If you cruise at 4800 rpm that runs hotter too verses rpms in the 5000's. What kind of oil has it been using over the years?
If you have some higher hours on the engine it may be time to have the oil cooler flushed. This does happen to people, but they never consider the cooler reducing the flow over time from garbage in the system. (i.e. lead from fuel, hose debris and sludge from water in the oil)
If you have changed any oil hose then a close look to see if the radius has been reduced in a bend?

If you changed nothing and this just happened out of the clear blue then think about the oil cooler. You can double check the oil temp sender by swapping the wire from a CHT (exact same sender) and take a flight and see if the temp is the same, but it will read on the CHT sender reading. You could swap the actual senders, but a wire is usually quicker and easier for a quick down and dirty test.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Gordon Grant

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Re: High oil temp on 912UL

by Gordon Grant » 8 years ago

Gordon Grant

3 7 15

The Airmaster is an electric constant speed unit that can also be used manually in flight. Mine is set for 5600RPM for Take Off and Climb and 5200RPM for Cruise. I usually leave it at that, but have found that setting it manually to 4800RPM at 27inches MFP gives sligtly better cooling.

The engine has done 474 hours and has always been run on the Rotax recommended oils (can't remember the exact make but it was the Shell motorcycle oil pror to switching to the Aeroshell Sport Plus). Oil and filter are changed every 6 months or 50 hours and I only use ethanol-free Mogas. The oil tank had no sludge when I cleaned it out.

I forgot to mention that I had already swapped the wires betwen the two temp senders and the high readings moved with the swap. I replaced the oil pipes in case they were collapsing/blocked internally and had my work checked and signed off by an LAA Inspector who said the pipes were routed correctly.

The oil pressure is 4.5 Bar at start and drops to 2.5 at 'normal' temps and then to 2.2 when temp rises to 130C. These figures are slightly lower than previous years - is it at all possible there may be aproblem with the oil pump? I will try flushing the oil cooler.

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Re: High oil temp on 912UL

by Roger Lee » 8 years ago

Roger Lee

127 5.2k 4.78k

Hi Gordon,

"I usually leave it at that, but have found that setting it manually to 4800 RPM at 27inches MFP gives slightly better cooling."

This would be more in line with what we see with only ground adjustable props here in the US. I don't have any in flight adjustable props here so I have no real rpm vs temp numbers to share.
Maybe some of the other owners here can chime in with some rpm and temp numbers with in flight adjustable props.

Your takeoff and climb rpms are fine, but higher rpms means more work and more work means more generated BTU's even though it seems the prop would be unloaded more. There must be a crossover point between unloading the prop and engine work that produces extra heat. Many in the US with only ground adjustable props have around 4900-5000 rpm on takeoff. Of course that can easily change depending how you take off. (i.s. flaps vs no flaps, hard climb with less speed vs shallow climb with speed)

Even though you changed oil hoses routing may not be the only issue. Anytime someone changes hoses and there is a change that is my #1 suspicion until proven otherwise. If they have a bend and it is a tad too tight the hose when it gets hot may start to flatten just a bit which reduces the oil flow which in turn raises temps. If you have any bends in the oil hose you need to check this while they are hot. If any are in question then either re-route the hose for less of a bend or install a spring inside the hose to prevent it from flattening. The spring will keep the hose in a round fully open shape and keep good oil volume flow. I have done this countless times with great success and never an issue.

I would also do that cooler flush. Do it backwards from the normal flow.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Gordon Grant

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Re: High oil temp on 912UL

by Gordon Grant » 8 years ago

Gordon Grant

3 7 15

Hi Roger,

I will certainly have a look at installing the springs to make sure the bends are OK.

Today I swapped the Oil and CHT gauges back to their original positions and checked and cleaned all the wiring connections, particular the earth, but I did not find anything obviously wrong. I went flying and although the OAT was the same as yesterday (19C) things were somewhat different. I climbed at full power to 2500ft and levelled off with the oil temp at 125C. Cruising at 5200RPM for 10 mins reduced the oil temp to 115C. Climbed to 3000ft, cruised for another 15 mins and the temp reduced to just under 110C. It would probably have come down further but I had to return to base as I was short of time. Interestingly, the oil and CHT temps dropped considerably during the descent, as they should, but recently this has not been happening. Could it be that an earthing problem has been causing problems with my temperature gauges?

Regards

Gordon

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Re: High oil temp on 912UL

by Arthur Götz » 7 years ago

Arthur Götz

6 31 1

Gordon, did the higher temperatures coincide with your switch to Aeroshell Sport Plus 4?

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High oil temp on 912UL

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