Other than the engine, there is really no difference in a CLK500 and CLK550. The M273 engine will likely not have any issues with leaky valve cover seals like the M113. It does, however, have issues with leaky cam plugs, oil centrifuge cover, and camshaft adjuster solenoid seals, but those are all cheap and easy to replace.

 

Be aware that the later ,,like 05 on, 500's have the seven speed trans 722.9 , same as the 550 , but perhaps more trouble and harder to service than the 5 speed 722.6.
That's why I went for a 2005 CLK55 . M113 with 722.6 ,,
I have not driven a M273 powered car , I am sure they would be good, but on paper the performance and fuel consumption did not appear to be all that much better than the older cars in my opinion.
M273 is more complex ,DOHC VVT etc more things to go wrong possibly ,but easier to change spark plugs than M113.

 

The 5.5l M273 engine is a monster. The CLK550 outperforms the CLK55. Yes, the 722.9 transmission is a concern, but the MY2008 and later versions should be fine and just as reliable as the 722.6.

 

0 to 60 times are the same , but the seven speed may give smoother shifting and uses about half a litre less fuel per 60 miles.
So it all depends what you prefer...:wink

 

I have to admit, I really do like the transmission in my GLK, it does shift better than the 5-speed in my w203. I've found an 07 CLK550 with an engine # that is outside the affected range. Given that the 7-speed was around in the CLK since 05, I'm assuming it should be better sorted by 07. It sounds like the 550 engine itself isn't that much more complex than the 500, easier spark plug replacement at least.

 

Hey, how did you find out that yours was outside of the affected range? I'm currently looking at an 07 clk550 as well and would really love to know whether it's inside or outside the affected range!!
WDBTJ72H87F209482

 

Actually, the 722.9 was still problematic in MY2007. I am not sure when it got better but definitely by MY2009, maybe by MY2008. The main issues is caused by bad internal speed sensors that will require replacement of the conductor plate. This also happened on 722.6 transmissions, but on those, the job can be a DIY and is not terribly expensive. On the 722.9, the ECU is internal, embedded int he conductor plate, which makes the part more expensive, but it also requires SCN coding as it is now a part of the anti-theft system. That pretty much makes it a dealer-only job and they charge around $1500.

 

A one-time expense of $1500 is livable, if that means better shifting and mpg for the rest of the ownership of the car.

 

Replacing the conductor plate likely won't improve shifting and MPG. It will correct the problems associated with a bad speed sensor, which will start out with the occasional limp mode, and progress to failure to shift into gear when cold.

 

I'm saying better shifting and mpg than the 5-speed, so that the potential expense of the 7-speed over the 5-speed is worthwhile.

 

Ah - I understand! You are exactly right!

 

MBZ's published 0-60 times are the same, but the CLK550 is faster. Even the cabriolet goes sub-5 seconds, where the CLK55 is about 5.1. The coupe is closer to 4.7. The reason for the gross understatement was so that buyers of MY2006 CLK55's would not be so angered to discover that they could have bought a MY2007 CLK550 that was faster, but for $20K+ less.