[Mac]

I've had both, and a couple of other diesel's over the years. It really depends on whether you need it for towing or not and how much you drive.

A CDI is complex engine with a turbo, inter-cooler, urea injection, running extremely high injection pressures, etc. Other than the balance shaft issues on earlier models, the gas engines are more reliable, simpler and less expensive to maintain. Other than oil and filter changes, the gas engine will go almost 100K miles with basic maintenance. The diesel is expensive to service because it needs fuel filter changes every 20K miles, ad-blue, etc. The fuel filter and air -filter service is expensive because it's a 1 hour job or more to get at the parts. A complete diesel service is $800-900. Diesels are also notoriously hard on batteries. Like the fuel and air filter, they are also conveniently located......under the passenger seat under the carpet.

I have a 320CDI. When I replace it, I'll get a gas 350 since we drive about 10K miles a year. The diesel pulls strong once it's fully warmed up. Short distances in cold weather, you have to take it easy and it's way down on power. One more thing to watch is fuel contamination. All you need is one idiot to put gas in a diesel at a full service station or a family member not paying attention and you've got a $5000++ problem not covered by the warranty.

I did a bit of research before ordering a BlueTEC. It will be my first diesel so, I do not speak from personal experience. However, based on what I've read the BlueTEC the highest resale value. A diesel is a more expensive engine because it has to be made better to withstand the higher pressures. A diesel is obviously more efficient but rather than compare the fuel economy to the gas-350 the better comparison should probably be to MB's V-8 --e.g., the diesel is getting about 10 mpg more on the highway. Diesels are renown for their longevity. From what I understand there is very little difference in service costs over the life of the car --e.g., there won't be a need for a tune-up at 100K miles. Meeting the blue state regulations to have a 50-state car may skew the service cost stat in favor of gas engines but still, with the diesel you do have the cleaner car. It definitely will be difficult to pump regular gas into a diesel but I suppose anything is possible.

 

[Mac]

I think you begin to consider purchasing a diesel when -- if not for the diesel option -- you would only have considered MB's 8-cylinder for your ML. For me, that's the real comparo -- not between the two 6s.