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rotax 4-stroke - coolant

912UL, 912A, 912F, 912ULS, 912S, 914UL and 914F Engines

what coolant should I use?

The aircraft cooling system is designed and tested by the aircraft manufacturer, and as such the coolant used should be that specified by the aircraft manufacturer.  In the absence of this information, refer to Rotax Service Information SI-912-016 on the selection of suitable operation fluids for 912 & 914 series engines, this document is available to download from the documentation section at www.rotax-aircraft-engines.com

Please contact the aircraft manufacturer for instructions on draining / filling & bleeding cooling systems.

All information provided here is correct at the time of publishing to the best of our knowledge, but Rotax recommendations may change at any time without our knowledge.  It is the engine owners responsibility to ensure that the engine is fit for flight at all times.  The information is provided here free of charge and with no obligation from us to the consumer.  To ensure that you have the correct and most up to date information, you should refer to the current Installation, Operators and Maintenance manuals for your engine.  The information provided here may not be valid for aircraft outside the UK.  Click here for ConAir SportsTerms& Conditions, including website usage policy.

* Rotax Service Information available to download from the documentation section at www.rotax-aircraft-engines.com

If your aircraft is not listed here, feel free to let us know and we will try to obtain the necessary information to add to our list..

what coolant should I use?

what radiator cap should I have?

do I need a coolant temperature gauge?

how often do I need to change my coolant?

coolant leaks

tell tale signs that an engine has been overheated

what radiator cap should I have?

Information regarding the suitable radiator cap for your engine / coolant combination is available in Rotax Service Instruction SI-???????

In brief, the pressure is stamped on top of the radiator cap.

     If you use Evans NPG+ you can use either 0.9 bar or 1.2 bar radiator cap.

    If you use 50/50 Glycol /water then only the 1.2 bar radiator cap should be used.

If you have another coolant or ratio combination, you will need to contact the aircraft manufacturer to find out  the correct radiator cap specification.

do I need a coolant temperature gauge?

Only if you use 50/50 glycol / water - please refer to Rotax Installation Manual orService Information SI-912-016.

Please note that the engine is NOT fitted with a water temperature sender.  The senders installed in cylinder heads 2 and 3  do not go in the coolant circuit - they are for Cylinder Head Temperature (CHT ) only.  To install a Water Temperature Gauge (WTG) you will need to install a sender in the water flow which can be achieved with a special T piece in one of the hoses on the cylinder head.

how often do I need to change my coolant?

Please check with the coolant manufacturer.  If in doubt, every two years would probably be advisable.  Evans NPG+ is a life time coolant and does not need to be replaced - just topped up.

coolant leaks

Water leaks are uncommon, but can be a sign of overheating.  The coolant elbows are threaded into an adaptor plate or directly into the head and the thread is sealed with Loctite.  Moving the elbows or overheating can damage the seal which can be repaired by removing the elbow and applying fresh Loctite.  If you experience a leak, check:

1) Hoses & clamps.  Hoses are 5 year lifed and if old may perish.

2)  The water pump has a small “leakage bore”.  If is located on the underside of the magneto housing.  If water is escaping for the leakage bore the carbon faced seal on the water pump shaft needs to be replaced.  

3) The water pump gasket between the housing and mag housing.

4) The water pump drain bolt - the lower bolt should be stainless steel with a copper gasket - the drain bolt will leak if the copper washer is damaged.

5) The cylinder head upper elbows are screwed into an adaptor plate and loctited in place.  The adaptor plate is then fixed to the cylinder head with 2 screws and sealed with an o ring.  If coolant is seeping from around the elbow, it is possibly where the elbow screws into the plate rather than the o ring seal.  If the plate is removed, the o ring should be replaced.

6) The Cylinder head lower elbows are threaded into the head - to remove them warm the head and unscrew.  Refit using Loctite 648.

7) The water pump housing elbows are threaded into the housing - to remove them warm the housing and unscrew.  Refit using Loctite 648.

WARNING - if the coolant fittings are leaking, it could be due to other factors, I.e. They were moved when the engine was fitted into the aircraft, or more seriously if the engine has been overheated (overheating damages the Loctite seal)  In the latter case, some additional checks may be necessary - refer to Maintenance Manuals.

tell tale signs that and engine has been overheated

- Melting of the black plastic material in the centre of the CHT sender, which in turn allows the brass connector pin to fall out.

- The valve cover leaking oil and not  seating properly when using the standard o-ring.

- Leaking of the aluminium coolant socket where it is screwed into the underside of each cylinder head or into plate on top of each cylinder.

- Oil leaking  from the pushrod guides which are located under the cylinder head.

- The cylinder head bolts are loose.

- The rocker arm shaft  shaft becomes jammed in the cylinder head and cannot be rotated and will not slide.

- The valve guides have moved out of position.

- Oil is leaking between the cylinder head and cylinder.

If overheating is suspected, the hardness of the cylinders and cylinder heads needs to be tested.  This test requires specialist equipment and removal of the heads.  An engine that has been overheated  will usually continue to run, but will exhibit some or all of the symptoms above until the “soft” heads are replaced.  The engine will also begin to lose power due to loss of compression caused by losses in performance of the valve train.