456 or 550 which cost less to drive per mile

It is not much of a difference. The only thing I can think of is the non-M 456s don’t have hydraulic valve lifters, so the clearance should be checked from time to time. The 550 is lighter but run higher rpm at the same speed. Both are thirsty. A good thing. Because if they were not that expencive to run, a lot more would be seen on the road. I feel the quality is better on the 550 than 456, but the M is engineered and build two years later than the 550, so maybe that is better. I don’t think there is much of a difference. They are all beautiful and great !!

 

Not much difference and the maintenance schedules are pretty much identical, except for the necessity to adjust the tappet clearances with shims every 15,000 miles on the 456 and 456M, both of which have solid lifters. The 550 has hydraulic lifters. The self-leveling rear suspension system may require a little extra attention, too.

 

Once I got my M GTA sorted, it’s been very reliable and trouble free.
It is thirsty though, especially in the city.

 

My 2002 456M GT gets close to 15MPG using Shell V-Power 93 octane.

 

On my 2001 M, the pop up lights have been an irritant for the last 3 or 4 years.

Power windows also a mild irritant - don’t think the 550 has the same issue.

I think the 456 was a more attractiveness design when new, and has aged better. Of course this subjective.

Finally, as a family of 3, the 456 has been integral to many adventures.

 

Door windows and hydraulic rear suspension are issues the 550 doesn't have. They can be fixed, but they will need fixing again. The power seats on 456 have always been more trouble but I suppose it depends on how many of the functions you care to keep operating. Also in costs per mile even at current prices I think long term the resale will be better on the 550.