I watched every single race of him in F3 including live timing, you really would like to know about all his DNF's that year? Its really funny because people always tend to think that seeing DNF in the list means that most likely the driver had a lot of problems caused by himself. Just be honest, did you followed F3 that year?
I bet you didn't.
Here you have the exact reasons for each and one of his DNF that year. Silverstone and 2nd race Pau was due to himself, 3th race of Pau can be debated and the rest is/was mechanical failures. After Pau his career took a flight, his real career basically started during the Norisring weekend and before that only 2 big mistakes by himself.
In order:
Race1 -Silverstone Race1 - Suspension (Max fault)
Race4 -Hockenheim Race1 - DNF due to electrical failure
Race5 -Hockenheim Race2 - DNS due to electrical failure
Race8 -Pau - Race2 - Spin (Max Fault)
Race9 -Pau - Race3 - (Ocon squeezed Max into the pitwall causing a bend wishbone, raced with bend wishbone which eventually snapped and made him crash. Official warning given to Ocon)
Race10 -Hungary - Race1 - DNF due to Clutch failure
Race20 -Moscow - Race2 - DNF due to defective alternator
Race26 -Nurburgring- Race2 - Engine failure (Engine replacement caused him a 10 place gridpenalty for the next 3 races)
Race28-Imola-Race1 - Crash - Suspension (Max fault)
Max was in a new team with VAR, they didn't had good enough F3 Euro Series experience which hampered the team especially in some of the mechanical failures like the electrical problems they had during the Hockenheim weekend which they couldn't solve in time and caused a DNS for race2. Also the clutch gave problems for them. Besides of that Max suffered from a Engine failure when he was leading the 2nd race at Nurburgring. Not only he lost that race, he also was given a grid penalty for the next 3 races of 10 places due to mounting a new engine. The best part is, he took those penalties in Imola and was still on the podium in race 2 and 3. There you have the IF and what could have been.
Prema was an established team, they knew all the ins and outs compared to VAR for who it was all new with inexperienced drivers at that point. Looking at what VAR and in particular Max has achieved that year considering the amount of mechanical failure they had to deal with I think they couldn't have done it much better than they did. take next in consideration, New team, New driver that steps into F3 straight from karting in what was anticipated as one of the most competitive F3 fields in years. Ocon is good but......
Not that it changes anything for you, just saying.