Coolant

We installed a 914 new in our Europa back in 2005 and ran it for 1200 hours.  We replaced it with a new 914 in 2023.  We always used Evans in the old engine.  The new engine has the new cylinder heads so we are using DexCool as specified. There were no changes to the cooling system except to replace the old worn baffles that ensure air flow to the radiators. Strictly a maintenance item.

We have a GRT EIS so we monitor CHT using their supplied ring style CHT probes, mounted under the VDO probes on the original engine and screwed into the castings of the new engine. On the old engine we monitored coolant temp in the hose leading to the expansion tank.  The new engine we use the supplied sensors in the heads for coolant temp. We now have over 100 hours on the new engine.  What we notice is that the coolant temp on the new engine limits our initial rate of climb to keep within limits and at shut off, coolant temp immediately goes past redline. 

Here is some data:

Old Engine Coolant temp T/O 220 F  Cruise 190 F

                    CHT 230/240 F   Cruise 160/210 F

New Engine Coolant Temp T/O 245 F (higher if allowed) Cruise 210 F

                      CHT 210/220 T/O  Cruise 175/200 F

Older Rotax literature approved Evans while newer literature doesn't and of course it is prohibited with the new cylinder heads.  But it appears some are using it and we wonder if it would help our climb situation.  The old literature explained how boiling can cause pockets of vapor which prevent heat transfer while the higher boiling point of Evans prevents this.  Would it make sense to go back to Evans?