drchpeteros

2009 e350 4magic wagon

does anyone know the highway speed for optimum gas mileage for this car

CaliBenzDriver

50 to 55mph with properly inflated tires are the top official answers. Also get your 2x upstream oxygen sensors replaced so your V6 can reach peak efficiency again.

dvenneman

I’ve often wondered if the engine was “tuned” for max efficiency based on the Autoban and say 120 or 140km/hr as minimum speeds. But physics must dominate and I get 27 mpg - maybe 28 for periods of 65 mph and drafting and silly efforts like that which cannot be sustained.

I appreciate the O2 sensor suggestion above. Camshaft magnets and VVT solenoids and air filters and clean oil and waxed car also make a difference (?)

CaliBenzDriver

I forgot to mention tight old brake calipers that don't release well.

Test: Lift your wheel off the ground and rotate it to see that its really free-spining.

Results: obviously none of the wheels will be held crazy tight by released brakes. You'll find them to be more it less tight.

Fix: service caliper pin with new clean silicone lube to help release easily and quickly.
Clean brake fluid helps prevent internal rust that prevents caliper piston seals helping to retract pistons when released.... so flush fluid with new Dot3/4.

Modern luxury calipers feature multiple pistons in each brake caliper. More friction, more service!

drchpeteros

All good suggestions. Would changing the sensors really make that much difference? I changed my plugs for the first time at 122K (1000 mi ago) and I swear my mileage went down, at least around town, from 18-20 to 17-18. On the highway the best I get is 24 but usually 23 ish. It seems to actually do a tiny bit better at 72 than 65. Evey highway is different in terms of hills so it's hard to tell. I will definitely check the tore spin as well.

Is it bad (other than safety) to shift into N when gliding down long hills? I've done this several times on long hills and it gives a noticeable boost in MPG. The car is really held back by the gears but I'm not sure how good it is for the tranny to shift into N while gliding.

CaliBenzDriver

Good luck squeezing mpg out of your 2009 engine. I hope your not serious about saving money by coasting in Neutral.

The net tesult is you'll spend money to save gas, does that make sense?

Idling your transmission ATF oil pump and converter downhill guarantees a rebuild tranny in your near future.
Shaft bearings need to be lubricated and oil circulated to cool through the radiator loop....

Where on earth did you get that idea to save mpg?

Have you heard about the magic magnets over gas lines to atomise particles - some ppl swear by it.

drchpeteros

"Idling your transmission ATF oil pump and converter downhill guarantees a rebuild tranny in your near future.
Shaft bearings need to be lubricated and oil circulated to cool through the radiator loop...."

That line would have been sufficient to answer the question. There are a lot of people like me who are newbies and don't know a lot about cars, which is why we are here... To learn. Comments about magic magnets just discourages some people from asking questions (and pisses us off). I / we do however truly appreciate the helpful input by people in the know and we appreciate you all taking the time to answer these questions, minus the insults.

Where'd I get the idea? Funny you should ask. About 10-12 years ago when gas prices were high, I saw a segment on a news show a guy did on how he challenged himself to get maximum mileage out of a tank of gas. He would turn the engine off at every stop light, try to time things so he rarely had to hit the brake, glide downhill in N and even shut the motor off when gliding down long hills in N and restart near the end of the glide. Crazy stuff but he was getting some insane mileage out of a tank of gas. So of course, I fooled around with it, purely as a challenge, and gliding seemed to be the only thing that was easy and practical. I did however wonder if it was bad for the tranny but never asked the question until now. I did it in my 2000 Maxima a million times with no trouble and I've done it in this car a number of times with no trouble, but I lost interest in the challenge long ago. It was never about saving money.

CaliBenzDriver

If it was ok in your Nissan then it could very well be ok with this car also.

I am mostly open minded but biased to fix problems, not to create them.

These transmissions use ultra-thin ATF fluid to save gas and shift early to keep rpm down low.

The E-class is a heavy chassis fit for highway security. No way to rival with a Prius economy.

Overheated

Worn front and rear wheel bearings grind and I believe impede speed, smooth performance, and to an extent milage.

drchpeteros

How would I know if the wheel bearings need attention?

How long / how many miles can one expect out of the bearings?

Should they be changed as a matter of maintenance at a certain mileage?

drchpeteros

I agree with fix and not create problems and based on what you've enlightened me to I guarantee I'll never coast in N again.

dvenneman

So, I have a half mile or so downhill on my commute to work and I put my wagon in neutral and you do get better mileage. I keep my foot off the gas and pull it back to drive just before the flat.

based on the “ATF” quote above, I still don’t by the “buying a transmission” for this practice. Neutral to drive is not demanding anything extraordinary as compared to 4th - 5th. As evidence of this reasonable practice, we have a GLB 250 loaner right now and in ECO mode, Mercedes’ has the 8 speed auto trans do it for you - it literally outs the car in neutral when you go down hill.

So, maybe it isn’t so dumb. I have regularly serviced this transmission 3 times in my ownership and also by report on this and other forums, the 5 speed auto trans in the W211 is “bullet proof”.

I will say it is very tough in a commute to get over 23 mpg - I also note the other contributor above citing 72 mph seems to deliver better mpg than 50 - 65 and I’m not entirely sure that is wrong. I’m pretty sure however that you will do better at 55, 60, or 65 if you can stand it - but I’m stuck at 65 as my low tolerance.

well, let’s see what folks say now?

Overheated

Raise the front wheel off the ground. It should spin easily and without much drag or noise. Grasp the wheel by the sides and try to move it side to side. If there's play, inspect the bearings. There are DIY's here and elsewhere. Front bearings should be of uniform color and finish, not pitted or discolored. Grease should be thick packed green. The spindle should polish up without blemishes. They may simply need repacking and tightening, but may need replacement.The rears can be tested by checking spin and play, but replacement is a different ball of wax.

drchpeteros

Phew.. now I don't feel so stupid for the glide in N practice. Thank you for the input.

drchpeteros

And can I rotate the fronts with the car in P like I'd normally have it when jacking? Definitely going to check this. I have no grinding but I do get a "woo-woo woo-woo" sound at low speeds which I thought was just the tire wear on the inside edge as I was once told by my indy. Didn't really make sense to me but that's what he said.