Thinking about buying a w251, but have questions...




I'm considering buying a w251 but wanted to ask you guys a couple questions first. I've tried to do some research but not sure that has cleared anything up for me. I guess the main question is which year/model do you think is the most reliable? When looking at these, what is the main thing to check up on? Right now, the lower mileage ones I've found are the older 2006-2007 models. I've seen a few with 60-80k. Ive also seen one or two 2011 and newer with a little over 100k miles. What are your thoughts on that?
Thanks in advance....
Stay away from the diesels. Lots of problems and very expensive to fix.
Either way common issues are rear liftgate latch problems (replace with cheap aftermarket) , Various SAM issues. AC issues. You will have to changer rear airbag suspension probably (get the Arnot, easy to replace yourself)
Do get it checked out by a good indy shop.




Stay away from the diesels. Lots of problems and very expensive to fix.
Either way common issues are rear liftgate latch problems (replace with cheap aftermarket) , Various SAM issues. AC issues. You will have to changer rear airbag suspension probably (get the Arnot, easy to replace yourself)
Do get it checked out by a good indy shop.
Tailgate latch and lift mechanism and water intrusion into the spare tire compartment are the other common trouble areas I can think of. Water intrusion is especially problematic with Keyless Go because the Keyless Go module sits at the bottom of the spare tire compartment.
Oh, and the HID projectors on cars with the bi-xenon option have a habit of burning out the reflector surface. I have a thread on how to replace the projector with a better one. The replacement works for halogens too if you want to upgrade to real bi-xenon projectors.
Last edited by Tsumi; Sep 9, 2021 at 06:37 PM.




Thanks again for the help...
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Stay away from the diesels. Lots of problems and very expensive to fix.
Either way common issues are rear liftgate latch problems (replace with cheap aftermarket) , Various SAM issues. AC issues. You will have to changer rear airbag suspension probably (get the Arnot, easy to replace yourself)
Do get it checked out by a good indy shop.




I've been thinking, i might want to get a R500. I'd like a little more power, but just want to make sure its reliable. Right now I'm open to either one, just want to get a low mileage(under 100k,) 2009-2011 350 or a 500. Must have keyless go(hard to find) and heated seats. There aren't very many for sale in my area, so I'm not really expecting anything soon....
One other annoying thing about the M113 engine is the tendency for the valve cover gaskets to leak. I've replaced it twice; the first time with Elring and the second with OEM Mercedes. Still leaks. I've seen some posts where they said they filed down the bosses on the valve cover to get it to seat tighter. Others mentioned using gasket sealer. I'm going to try the gasket sealer and see how it does.
Generally I leave the adaptive suspension in auto, and it comfortable enough most of the time. If I feel like pushing it through an off ramp at high speed or carving through some mountain roads, I'll put it in sport mode. I only use comfort mode for long straightaways, i.e. i-5 in CA. It's too boaty in comfort mode for commute driving but simply floats on straightaways.
I got the OEM hitch for it and had a local shop replace the Class II receiver with a Class III receiver. Super comfortable towing our boat and you can hardly feel it back there (boat + trailer weighs about 3700 lbs).




I know the air suspension has been mentioned as a big problem, but that is not something i need to worry about. First thing I will be doing is a coilover swap and lowering with wheels. With that said, should I still stay away from the 06-08 350's?
Thanks.
There are two types of air suspension on the W251s in the US: rear only for load leveling, and 4 corner with adaptive suspension. Honestly they're not that big of a problem. You just have to plan for it as a maintenance item rather than an expensive repair. Rear air springs are $60-160 on RockAuto, depending on the brand. If you notice your car sagging, you should replace them ASAP because it can burn out the compressor otherwise. Though like you said, you can swap to coil springs and not have to think about them at all.
06-08 have these two major problems to think about: balance shaft failure on the early M272 engines and conductor plate failure on the early 7G-tronic transmissions. If you buy into those years and none of those have been addressed, make sure you budget for these repairs. Everything else on these cars are basically the same throughout the years.




I thought the Balance shaft issue was only for MY2006 - mid/late 2008. Are you saying every year m272 has the issue?
The balance shaft (and any other part for that matter) can fail on any engine. Wear and tear will do that. 05-07 had a significantly higher rate of failure, hence the lawsuit.
I know the air suspension has been mentioned as a big problem, but that is not something i need to worry about. First thing I will be doing is a coilover swap and lowering with wheels. With that said, should I still stay away from the 06-08 350's?
Thanks.













Thanks!
As for the latch, the latch pulling mechanism might not be pulling it in all the way. Do you notice any differences in the tailgate gaps between when it does and doesn't give the warning?




To answer your question, No there were no difference in the gaps. I checked a few times to make sure it was fully closed when getting the warning. It was fully closed every time...







