CLK430 More MPG To Be Desired?
 

Hello,
I recently drove my 2000 CLK430 convertible to Florida and was disappointed to only get 22mpg with all freeway driving, is this normal? The motor only has under 60k on it, clean K&N filters, fresh oil... ?? Any ideas on what can be done to improve the fuel mileage? Thanks!!

Sounds normal to me.

I would be VERY leery of a K & N on that car! oil on the air mass sensor will cost $400+

The restated EPA rating on the car is 15 city and 22 highway. How fast were you going? There's quite a mileage difference between going 60 and 80.

Thanks for the quick reply Doc.

My Corvette that had 1.4L and 100hp more also got 50% more mpg on that same trip... ah well. To bad 6 speed manual wasn't an option.

I wouldn't have chose the K&Ns, they were on the car when I bought it. I heard some green filter is supposed to be good, never really looked into it.

I was going between 60 and 80 the whole trip, probably closer to 75 for an average. I guess I was just expecting more, the car really could use another gear for expressway use.

The vette dosent weigh anything though.

I don't know the coefficient of drag for the convertible. Air resistance would dominate at those speeds. I assume the top was up. With the top down the MPG would suffer quite a bit I would think. You would do a lot better at 65 of course.

While the Vette weighs less and sets lower that to me is still no reason why a sleek yet smaller RWD V8 powered car got essentially the same mileage as my fat, offroad, 4wd, can drive through anything and tow 7500lb at anytime (and probably has about a .4 Cd) truck can, which also has a 1L larger motor with more power.

Yep, that was top up the entire way. I put a can of injector cleaner in it and cleared out the mileage for the last short partial tank, it got 23.3 on that tank of just flat beautiful Florida land. :cool: I'll run another can through it to make sure it is clear but that to me is just crazy that it can't hit at least 25 with stop-less driving.

It is not crazy if you are going 75 and the soft top has greater drag than a hardtop which is a reasonable assumption. Air resistance increases at the square of the speed. So from 65 to 75 the air resistance increases 37%. Without the drag coefficients it is hard to say how significant the soft top is but it could be significant.

For what it is worth, I calculated the mileage on the way back... there were three tanks used; 23.4, 24.5, and 25.9mpg! Quite a notable improvement, the strange thing was the best tank was going through the mountains.