Legin

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Well my first post. I am looking to buy a used SLK 55 around 05 plate.
I wasnt sure about the car due to the auto box so decided to hire one for a day just to be sure, the MPG averaged 15 but I have decided its for me, if somewhat softer than my usual buys. I have some questions. First the hire car roof wouldnt detach from the windscreen so back to the dealers, I hope this isnt a reflection of inherent roof reliability problems, is this a known one ?
Are there any other issues I should watch for, reliability in general ?
What mpg can i expect with more normal driving pattern ?.

etyu

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Welcome legin. Please let us know your location as options and features are different in different countries.

I've had a prior 280 for about 18 months and the 55 for 11 months. Both are without any roof issues. My average mpg is 18mpg (city and highway).

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Eddy

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Legin

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Im in the UK

DansSlk

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No real roof issues to be aware of other than some housekeeping such as the importance of running the roof ideally monthly because the fluid contains the lubrication (like the AC system does), the need to keep the roof's alignment protected (very easy to put it out and cause rattles or leaks) oh and keeping the seals lubricated.

In my modified 55 i can return 30 MPG, if you where using an auto mode on a hire car its asking for trouble with an adaptive gearbox.

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Legin

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Not sure I understand what you mean using auto mode on a hire car = trouble ? Can you clarify, I tried it in C /S/M modes.

cyberdrakon

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the automatic transmission has a learning function based on your driving input...not very good for test driving as it might have been babied or harshly driven.

FishtailnZ

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In "easy" (I won't say "normal" ) around town driving I average right around 20 mpg, and with cruise set to 65mph on the highway I get 27-28mpg. Of course, dip heavily into the throttle and all bets are off .

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- Bill

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R.I.P. 2006 SLK55 Caspian Blue/Beige
Stock 1/4 mile results: ET 12.72, trap 110.80, 60' 1.80

Some guys they just give up living and start dying little by little, piece by piece. Some guys come home from work and wash up and go racin' in the street... - B. Springsteen

DansSlk

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Thanks buddy!

Legin - thats what i mean, like they say nothing drives like a hire car and when the car is learning all that its consumption is going way up.

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linuxpro

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I don't understand how anyone could get this kind of fuel mileage on an SLK55.

With my SLK350, my average mileage (50/50 city/highway driving) has been around 18-20mpg. And I've got the Green filters installed. How is it possible that I'm getting worse mileage on my V6 than people are getting on their V8s?

FishtailnZ

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Heavy foot? Those city numbers aren't "my" norms either, but I have gone easy on the car for a week or so at a time just to see what I could achieve. The highway one is common though, as I just stick the cruise on 65 and leave it there on those long distance highway trips. I've seen some 350 owners post about 30+mpg numbers, so it is doable...just not as much fun!

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- Bill

Waiting on a 2009 C63 Fire Opal/Alpaca Premium+Media

R.I.P. 2006 SLK55 Caspian Blue/Beige
Stock 1/4 mile results: ET 12.72, trap 110.80, 60' 1.80

Some guys they just give up living and start dying little by little, piece by piece. Some guys come home from work and wash up and go racin' in the street... - B. Springsteen

linuxpro

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A week or so after buying my SLK350, I took it on a drive from Seattle to Spokane (about 300-400 miles). As an experiment, I put it on cruise control at speeds of 60, 65 and 70mph for 1 hour each. At all 3 speeds, I was driving in 6th gear. I was driving in a completely straight line, at an elevation of approx 1-2k feet above sea level. There was no braking or change in speed during those periods. I recorded fuel mileage rates of:

60mph for 1 hour: 25.4mpg
65mph for 1 hour: 26.1mpg
70mph for 1 hour: 25.8mpg

I am an engineer. When I test a theory, I use a repeatable process to verify that my results are reliable. I find any claims of 30+mpg fuel mileage on an SLK350 to be rather specious (and extremely doubtful).

My girlfriend's 1997 Toyota Tercel, which has a 1.8L 4-cyl engine (half the displacement of the V6 in the SLK350) w/ variable valve timing, gets an average 25-28mpg in mixed city/hwy driving with her driving (conservative). I have recorded fuel mileage rates in her car under the same test conditions described above at approximately 34-35mpg, which are the best fuel mileage rates I have ever seen in any gasoline-powered car. There is no way that any V6 or V8 will ever see mileage rates anywhere close to this. For a quick comparison, my mother owns a 2007 Toyota Camry with a 2.4L 4-cylinder engine with variable valve timing and an extremely conservative A/F tune that gets, at best, 26-28mpg on the freeway.

I would consider any 27+mpg mileage claims on the SLK350 to be rather dubious. Perhaps if you were to tune your A/F mixture extremely lean, you could get around 27-28mpg, but then you would be risking engine damage.

And any claims close to this on any V8 would be implausible. As the displacement of an engine increases, fuel mileage will always decrease. There is simply no possible way to burn a greater amount of fuel at a fixed speed and somehow burn less fuel. The only way to reduce the amount of fuel being used is to decrease the displacement, or reduce the amount of fuel in the A/F mixture being used by the engine (going "lean"). Modern engines do accomplish this with a mix of variable valve timing and ECUs that can adjust the A/F mix on the fly, but it still will have a limited impact on your fuel mileage. Decreasing the injector droplet size (or vaporizing the fuel), heating the fuel, and other tweaks that are currently being experimented with by auto mfr's, could theoretically increase mileage on modern engines, but all those things are experimental.

The simple fact is that you will be lucky to ever see the EPA mileage ratings for any engine with the drivetrain, ECU, etc as supplied by a manufacturer. The EPA rating on the SLK55 is 20mpg freeway. That means if you were to drive it very conservatively, you should expect a mileage of around 18mpg in 100% freeway driving at the most efficient RPM possible. You could possibly get 20mpg, but it is doubtful you will ever see that, since those numbers are generated on a test bench with zero drivetrain loss (and the engine running at a fixed RPM). I suppose if you were to tweak your A/F mixture, heat the fuel before it was injected into the engine, and run some kind of higher-octane mix (say some low mixture of E85 or something) you could probably achieve 20% better mileage, but that is just not going to happen.

If you are looking for realistic mileage expectations for any vehicle, the general rule of thumb is to subtract 10-20% from the EPA ratings for the vehicle and expect about that. If you were to do this with the SLK55, you should expect:

100% city: 13-14mpg
100% fwy: 17-18mpg
50/50 city/fwy: 14-15mpg

Those numbers would be under "prime" conditions; i.e, no traffic, no heavy braking/acceleration, etc.

DansSlk

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OK linuxpro with my quoted figures they are in UK MPG so they are going to look higher but with Legin being in the UK they are an accurate reflection of what he will see at motor/highway speed.

I wouldn't want to accuse the others of fudging figures mind you because the 55 can be a cruiser when she wants to be and I'm sure they can back the numbers up with proof

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linuxpro

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I'm curious, what modifications are giving you 30mpg on a 5.5L V8?

If this is true, I have a former mechanical engineering professor that would very much like to talk to you. When I was getting my engineering degree, our university was taking part in a US govt-sponsored program that offered a significant award (I believe it was in the neighborhood of $50mil) to any university that could develop a 4.0-5.0L V8 gasoline-powered engine capable of 30mpg (one of the requirements was that it must run, at most, 91-octane gasoline) in real-world driving conditions. Out of the ~40 universities that were participating at the time, 0 were successful. Our university had about 10 PhD mech engineering students working on it, most of whom went on to work for various auto mfr's due to some rather groundbreaking research involving exotic-alloy bearings, atomized vapor injector tech, continuously variable transmissions, pre-injection fuel heating mechs, etc. One of the students went on to Nissan, and helped develop their current CVT technology.

I'm wondering if perhaps there is a language barrier happening here. I've heard many Europeans give rather exotic MPG numbers for their cars, based on faulty calculations converting L/KM to MPG (or other unknown reasons). I'm thinking that this must be the case here.

linuxpro

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I would still be very interested in your mods, as I think my SLK350 could do a bit better. Would you be willing to share any info with us? Don't worry about MPG, if you knew your mileage increases by percentage, etc, that would be extremely helpful and interesting to me at least.

Thanks Dan!

FishtailnZ

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On my most recent highway (aprx 200 miles) trip the computer readout gave me a figure of 8.9L/100km on the end - that equates to 26.4mpg. I've gotten as low as 8.7L/100km, which is a bit over 27mpg. That's US gallons too using the following convertor:

http://www.onlineconversion.com/fuel_consumption.htm

Even my regular around town driving usually nets me in the 13.5L/100km range, or about 17.5mpg. Those EPA figures you posted are real bad, only on track days (or cruise nights in Mexico *L* ) have I seen numbers down in that range.

Is your car a manual or 7-speed? Maybe the auto is a big more efficient?

Other than that I don't know what to tell you - numbers on paper are one thing, but these are my real world figures, whatever the EPA has to say .

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- Bill

Waiting on a 2009 C63 Fire Opal/Alpaca Premium+Media

R.I.P. 2006 SLK55 Caspian Blue/Beige
Stock 1/4 mile results: ET 12.72, trap 110.80, 60' 1.80

Some guys they just give up living and start dying little by little, piece by piece. Some guys come home from work and wash up and go racin' in the street... - B. Springsteen

dltslk

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This is the only way I know to drive the 55! I average 16-18, oh well that's what I bought it for!

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David

dltslk

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Uhh, Dan doesn't have a 5.4L he has a 6.1L Brabus putting out >500HP IIRC.

If I'm mistaken please correct me Dan, didn't mean to speak for you mate!

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David

DansSlk

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Thats bang on the money mate

Linuxpro, i really don't know what to say man, i wish i could tell you i modded this, this and this to get the consumption figures i have but in reality i paid no attention to fuel consumption in my modding plans, everything was about horsepower and torque so the consumption is just what i was left with afterward.

The figures are about the same as the SLK was when stock so no real loss for me, I'm sure they would have decreased somewhat from the Brabus mod's but I'm using ultra-lightweight moving parts in the engine and tranny that i think help compensate for it but i can't be sure since they where for extra power output and strength also.

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