Rotax Coolant stuff

[Wilfred]

 

 

 

 

 

 

 

 

 

 

After an investigation into a few isolated field reports, it was discovered that in some instances conventional 50/50 water - glycol coolant mixture could begin to boil off before the maximum cylinder head temperature was reached.

 

 

 

 

 

To address this issue and maintain the highest level of flight safety, Rotax issued the initial version of Service Bulletin SB-912-043 /

 

 

 

 

 

SB-914-029 in September 2004. This bulletin changed the coolant specification for the 912 & 914 engines from a 50 / 50 water - glycol mixture to a 'waterless' coolant with a much higher boiling point. This change was made to insure that coolant boil off could not occur in any circumstances provided that the engine CHT limits were respected.

 

 

 

 

 

Subsequent to the initial release of Service Bulletin SB-912-043 / SB-914-029, Rotax has continued to examine this issue, and now recognizes that for some 912 & 914 engine installations conventional 50/50 water - glycol mixture coolant may be a viable alternative.

 

 

 

 

 

Conventional 50/50 water - glycol coolant solution is inexpensive, readily available and has excellent heat transfer properties.

 

 

 

 

 

Understanding the benefits provided by conventional water - glycol coolant in some applications, Rotax has now released a new revision of Service Bulletin SB-912-043 / SB-914-029. With the release Service Bulletin SB-912-043 R2 / SB-914-029 R2, use of conventional 50/50 water

 

 

 

 

 

- glycol coolant is once again allowed, provided certain conditions can be met.

 

 

 

 

 

In order for a 912 or 914 series engine to be safely operated with conventional water - glycol coolant, SB-912-043 R2 / SB-914-029 R2 mandates that both cylinder head temperatures AND coolant exit temperature must be monitored at all times. Coolant exit temperature must never exceed the boiling point of 50/50 water - glycol coolant mixture AND engine cylinder head temperatures must never exceed the maximum permissible values set out in the appropriate engine Operators Manual.

 

 

 

 

 

To meet these requirements a coolant temperature sensor and cockpit mounted coolant temperature gauge must be installed in addition to CHT instrumentation. The coolant temperature sensor must be installed in the coolant line between the outlet of the expansion tank and the inlet of the coolant radiator (please refer to the Cooling System section of the appropriate engine installation manual for more details).

 

 

 

 

 

Installation of the coolant temperature sensor must not impede or restrict the coolant flow. The installed coolant temperature gauge must be appropriately marked with the maximum allowable coolant exit temperature.

 

 

 

 

 

Installation of the coolant temperature sensor and gauge will allow the pilot to monitor the coolant temperature throughout the entire engine operational range. If for any reason the coolant temperature approaches or exceeds the maximum permissible value (approx. 120 C (248 F) in a cooling system pressurized to 18 psi (1.2 bar)) the pilot will be able to take the appropriate action (reduce power setting and / or terminate flight).

 

 

 

 

 

Once again, installation of a coolant temperature gauge DOES NOT alter the requirements for the monitoring of engine cylinder head temperatures and respecting published CHT limits.

 

 

 

 

 

In some aircraft installations, the liquid cooling system may not be able to maintain a coolant exit temperature below the boiling point of conventional 50/50 water - glycol coolant. This may be due to the size of the coolant radiator, the design of the engine cowling, operating profile, or other related factors. In applications where the coolant exit temperature may exceed the boiling point of conventional water - glycol coolant, SB-912-043 R2 / SB-914-029 R2 requires the use of 'waterless' coolant only.

 

 

 

 

 

When 'waterless' coolant is used, monitoring of the coolant exit temperature is not required. The boiling point of the 'waterless'

 

 

 

 

 

coolant is higher than the maximum allowable cylinder head temperature, therefore the coolant cannot be boiled off without exceeding the engine CHT limits.

 

 

 

 

 

Use of 'waterless' coolant DOES NOT alter the requirements for the monitoring of engine cylinder head temperatures and respecting published CHT limits.

 

 

 

 

 

In cases where 'waterless' coolant is used and engine cylinder head temperatures exceed the maximum permissible values, the coolant system must be repaired or modified in such a manner as to increase the cooling capacity of the system.

 

 

 

 

 

More information regarding coolants for 912 & 914 series engines, including recommended brand names, can be found in Rotax Service Information SI-912-016 / SI-914-019 (August 2006). All owners & operators of 912 & 914 series engines should obtain a copy of this Service Information document.

 

 

 

 

 

If there is any question regarding the selection of the correct coolant for a particular engine installation, the engine owner / operator is strongly encouraged to contact the nearest authorized Rotax Service Center or their aircraft manufacturer.