HereÂ’s my pull-out-all-the-stops procedure for ease of starting an IO-550N with the least possible engine wear. Mine is in a Lancair so the Cirrus crowd here might see some differences in the area of priming. Input welcome, there’s always room for improvement in all aspects of flying:
- preheat if available. CHTÂ’s above 100Â°F is best *
- battery side of master on, alternator side off **
- advance throttle 1" prime 5 seconds, (10-12psi on guage) with mixture 3/4Â” back from full rich ***
- throttle closed
- vapour suppression switch on ****
- engage starter, aim for 800 RPM for the first minute *****
- vapour suppression switch off immediately after start
- alternator switch on
- 900-1000 RPM once CHTÂ’s are above 150Â°F or so.
- (delay runup until at least 120Â°F oil temp, 150Â°F is best Â– the 75Â° in the manual is not enough for me)
- The hotter the better. Even if the engine will start fine at ambient temperatures, this will reduce post-start wear
** Keeping the alt switch off makes sure all electrical current goes to the starter, none to alternator field coils,
plus the alternator presents less drag torque when there is no primary field current.
*** 5 vs 7 seconds because the vapour suppression step provides the rest. Mixture 3/4Â” back on my plane because I have
my mixture set very rich and the 3/4Â” back position gives the best idle, which presumably also leads to the easiest start
**** some people use the boost pump, itÂ’s higher pressure and cuts out automatically. ItÂ’s too much fuel (=fire hazard and hydraulic lock risk) for my taste
***** this is another attempt to lower post start wear. If done very well, the voice annunciator will say that the alternator is off line even if youÂ’ve
set the alt side of the master to on during the start. I take this as a sign of a great start. Momentarily increasing the RPM to about 900 brings the
alternator on line.
If youÂ’re in really serious cold, there are 2 more things that could be done:
- hand turn the prop before the start to circulate some oil and unseat the moving parts,
- use an external power supply connected to the external power plug to get more cranking power and not use the on-board battery.
IÂ’ve never had to resort to any of these despite a couple of Â–25Â°C OAT starts.