Oil cooler flush

by Neil Cooper in 912 / 914 Technical Questions 7 years ago

I'm about to change all my oil hoses, but am wondering if I need to clean out the aluminium oil lines and oil cooler with some sort of flush. Is there a product that is acceptable for this sort of job?

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Re: Oil cooler flush

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.96k

It all depends on WHY you are changing the Oil Hoses.
Is this just routine preventative maintenance?
Or, have the hoses disintegrated and fouled the oil system?

If there is no reason to believe there is contamination in the Oil,
You can drain the hard lines and cooler, Blow them out with air, or do nothing at all.
The amount of Oil in the lines is minor compared to the total volume of oil.
You are essentially just doing an Oil change and replacing a few feet of hoses in the process.

If there is known contamination in the Oil; The cooler will need to be replaced and everything else removed and thoroughly cleaned.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Re: Oil cooler flush

by Neil Cooper » 7 years ago

Neil Cooper

23 67 92

I don't think there is contamination. I am just doing it as part of the five year rubber replacement (although this engine has had them since 2004, previous owner did minimal maintenance) I have been trying to source a small oil leak that has appeared in recent weeks though, and though replacing the oil hoses would be a good start. I've also noticed a drop in oil pressure as oil temp increases which is different to what the indications used to be. I've checked the gauge earth and am going to replace the sensor. It doesn't seem to be going through any oil either.
My readings are:
Indicated Temp (°C) indicated pressure (bar)
89 - 2.9
94 - 2.8
100 - 2.5
110 - 2.2
115 - 2.1
120 - 1.8
125 - 1.7

Previously the oil pressure would be around 2-3 bar at typical oil temperature od 110 - 120°C

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Re: Oil cooler flush

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.96k

If you "feel the need", blow out the lines or just drain them.

Are your pressure readings at idle RPM or cruise RPM?

If at idle, as the Oil warms up, it "thins out".
At idle speeds, The Oil pump does not move an excessive amount of oil.
Does the pressure increase with rpm?
As the engine ages, the clearances within the engine increase and more oil passes easier through the bearings. The pressure will tend to drop as the engine heats up.

If your reading were at cruise RPMs, and the PO did minimal maintenance, the engine wear may be higher than might be expected for the age. How old is the engine and how many hours are on it?
A recent oil change may have cleaned up the engine causing the Oil an easier trip through the system.

What engine is it?
And where is your Oil Pressure Sender located? <---<<< !!!
The Oil Pressure regulator controls the pressure as the oil leaves the pump.
The pressure within the engine will differ from the pump pressure.

Before you start replacing parts for no valid reason, Remove the sender and screw in an actual gauge to confirm the pressure.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

Thank you said by: Neil Cooper

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Re: Oil cooler flush

by Neil Cooper » 7 years ago

Neil Cooper

23 67 92

The pressure readings are at cruise RPM of 5200. The pressure does not seem to change with rpm but it does with temperature. At cruise in cooler air of say 22°c the oil temp will be 110° with a pressure reading of about 2.2-2.3 bar perhaps, but as soon as I climb at full power (5500rpm) and the temp goes to 120° then the pressure drops to 2 bar or less (indicated) I have a 912ULS built in 2004 and has 530 hours and yes, I did a recent oil change. I change the oil every 50 hours but never run avgas nor has the engine ever has avgas run in it. My oil pressure sender unit is screwed into the oil pump housing. I am waiting for a mechanical gauge I have ordered to check the actual pressure.
The engine would have the old ball bearing type oil pressure regulator, but not sure if this should be upgraded.mthought I was possible the spring kinking problem in the old regulator would have anything to do with it ?

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Re: Oil cooler flush

by Roger Lee » 7 years ago

Roger Lee

125 5.12k 4.53k

You should do the 5 year rubber replacement. All hoses. Fuel and oil in fire sleeve which is reusable. The carb diaphragms, engine mounts, the carb balance tube 66mm hose, rubber carb sockets & "O" ring,

What oil are you using? If it is Aero Shell Sport Plus 4 then move on.
Double checking the gauge with a mechanical one is a good thing to do. Depending on what this tells you these are a few things to consider.
Your oil pressure issue may be a couple of things. It can change with temp especially at warm up from cold, but should be fairly stable at normal running temps. It could be the VDO oil pressure sender. It could be just a poor ground not making a good solid contact. This said this usually causes changes with rpm. As rpm increases the pressure drops and as rpm decreases the pressure increases. It could be the oil pressure plug, spring and ball bearing setup in which these should be replaced.

Always start with the most common and cheapest thing to work on or replace. Rarely is something an exotic problem.

If and when I blow an oil cooler out I run carb cleaner backwards through it and then follow that with high pressure air backwards.

p.s.
You should rarely ever see 120c (248F) and never 125c (257F) oil temps. Your system should be set up to avoid the high temps.

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

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Oil cooler flush

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