Blow out run
 

Why is there a procedure for a blow out run?

I have always thought that this is done when you had an unsuccesfull engine strat to get rid of the ecxess fule in the comustionchamber before another start-attempt, but now somebody told me also to this when you a hot start.

Please enlighten me....

Without identifying what aircraft your on, it is difficult to say.

Hot start on the B737 is will usually mean a RTG (return to gate). If you haven't exceeded any limits then technically you could attempt another start.

Perhaps they have a procedure where if the start was hot, the fuel control selector is placed to cutoff position but the starter is left engaged allowing the engine to continue turning over which blows cooler air through the engine for a longer period of time and reduces temperature.

Might be better than letting the engine sit there with a higher than necessary temperature. On some engines during a turnaround, you may notice how the still warm engine temperature decreases as rpm increases prior to lightoff. So motoring/blowout etc does cool the engine.

However, usually the approved method for a Blowout cycle(as it was called it on one aircraft type) is a separate starter engagement after it having been disengaged.

Dry motoring the engine also brings down the EGT faster so that another start attempt can be made.Normally EGT is required to be below 100deg. before introducing fuel. There should never be an actual "hot start" as monitoring EGT against RPM will show an impending hot start and fuel shut off to prevent it.