Date registered: Sep 2010
Location: Valrico, Fl
Mentioned: 0 Post(s)
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I'm going to go ahead and say what some people may be thinking. This is not as simple or as easy as you may want it to be.
There is likely an engine in existence that would deliver the MPG and performance you would like. Mercedes might even make it. But it is not a simple, bolt in swap.
Even when you get the exact same engine your car came with, it is a tedious job to change it. One that I've heard even a lot of seasoned mechanics complain about. It's removing the entire power plant of the car.
Then we move into a different engine going in. Now you have to worry about a whole new group of things. First, the simpler things like motor mounts. Unless the engine you find was available from factory in the same body style car you get, the engine will need to be fitted into the car and at simplest, need custom fabricated motor mounts.
Then you have to see if that engine is compatible with your gear box, or you have to see if an adapter is available. If not, you have to get a gearbox that will bolt to that engine, and then see if it can be mounted to your drivetrain.
Those are just a couple of simpler mechanical things. Not to mention fuel lines, coolant lines, etc. Then you want to get a '98 E-Class. That car has a great deal of electronics all over it. I'm not going to pretend to know the exact workings or dealings of them, but I do know the engine is completely electronically controlled, and to try and swap in an engine that didn't come with the car would take a great deal of electrical work, if it was possible. You would also likely not be able to get many of the cars features to function properly.
On top of that, you have the initial cost of the engine, plus the great deal of money you would have to put into adaptation hardware, a transmission solution, wiring, ECU's, possible software alterations, etc. And with a car that big, you are going to be hard pressed to get a whole lot more than 30-35 mpg out of it. Whatever extra fuel mileage you did get would likely take longer than the life of the car to offset the cost of the swap.
Best of luck.