MB-BOB

Here's a new topic (I think). Each time you refill your gas tank, your system recalculates the miles remaining for the new tank. Invariably, my MFD "Range" screen says 405 miles. Of course, it starts to drop immediately once you get to the first stop light.

Yesterday, I filled my tank, then immediately got on the Interstate and within 5 minutes (5 miles), my "After Start" display said I was making 25.3 mpg. So, I said to myself, "That's nice. I wonder how many miles I can go with this tank?" Checking the Range screen it said 405 miles. What? I would have thought it would say more, like 415 miles or something. Anybody else notice this? I'm wondering if there's a maximum reading that the system will display.

So, now I'm curious to know what your Range screen says after a fill-up? Please answer by specifying which C you have, and whether it's a stick or auto tranny. I think we all have the same size tanks (16.2 gal), but the C240 range might be higher than my C320, and the 4-Cyl. Coupes quite a bit higher. C32 AMG readouts are probably lower, yes? It would be funny if they all read 405 miles. And, no, this would NOT be lemon law material.

Related question: How far have your driven your C on a single tank of gas? Again, specify which car, please?

Yes, it's an off the wall topic, but I'm tired of reading about Buellwinkle's mighty Audio 10, OK? :p

revstriker

I have not checked this other than when I first fill up, or as I get close to empty. I wonder though what it is using to calculate the miles. Would it use the MPG after start, or after reset? I normally reset everything when I fill up. Next time I fill up I will take a look.

MarkL

I've checked the range occasionally just after fill up (2002 C240 6-spd), and I think it's around 385. BTW, my mpg screen usually shows around 19.6. I usually fill up when I'm just under 1/4 tank with about 230 or so travelled miles. Just recently I drove about 220 highway miles and my mpg went up to 29.9! That's the only time I saw my range value go over 400.

MB-BOB

One time I forgot to reset the "after reset" computer and the "Range" computer reset itself anyway. I'm thinking that the Range computer is not related (initially) to the trip computers, but maybe to the fuel level sensor. In other words, if the fuel level float senses a full tank, it resets Range to some default (like 405 miles), then the trip computer takes over and begins recomputing with usage. That rationale may be completely off base. But that's why I'm asking what everyone sees when they fill-up.

Fuzzo

on my car that range number switched more times than madonna's hair.. it woudl always start from 405 and always go up and down depending on my driving.. i did enjoy the time when i saw it at zero.. it was the day before I sold the car.. id idn't want carmax to have my has...so i drove it in wiht the light on and the range reading zero

dontwakemeup

I'm fairly positive that my range has read more than 405 but I'll have to check again during the next fill up. By the way can anyone beat my 530 miles on one tank personal record? I actually ran the range meter down to zero before filling up again. The best "after start" mpg was 34.0 for me.

Rick

My best mileage to date was a road trip to Canada for the Schumacher show...I mean F1 race.... in June. 35.5mpg on the highway (AC in EC mode, windows up, roof closed, cruise set at 74mph)
Range was (you guessed it) 405 miles with a full tank, immediately dropping to 368 miles when I got up to highway speed. The effective range before refuelling in Saratoga Springs was around 385 miles(~11+ gal refill, I'll have to check the reciept)...but thats with the 4cyl in my coupe.

You 6cyl folks might have different results.

trench

Nope, your rationale is 100% correct that's exactly what it does.

My coupe resets itself to 405 as well. One time driving back from LA I got the range up to about 450 miles after a fill up (I think the car calculates some percentage of the recent mileage into the next range calculation once it gets going again). The furthest I've ever gone is 370 miles on a tank - I usually fill up around 1/4 tank. In the older models with fuel injection it was possible to get air into the fuel lines via pump cavitation if the car was run too close to empty and one undertook vigourous maneuvers. Although considering peoples propensity to push things to the limit I could see where fuel pump development has reached the point that this is probably no longer a problem with newer cars.

Cheers, BT

zpeed

My gas warning light came on this morning so I switch the display to see the range = 35. I have to go to the jobsite before work so I was watching the range changing from 35-24-75-84. The road to the jobsite was up and down the small hill. As soon as I get on the Hwy it show steady at 30 and come down.

MarkL

I never thought the range was directly connected to any "reset". I think it just uses the amount of fuel currently in the tank times the average gas mileage. That value will fluctuate continuously based on the two measurements. You'll ask why it always seems to start from the same value, so maybe there's another factor in the computation.

Harris

I can only share my figures on the mpg side as I never fill up 100%. I only fill up 1/2 each time (dont want the car to carry too much weight).

The C32 has a "real time" fuel indicator because it moves so quickly. I've to refuel every other day. The mpg is very poor! But for a car with so many horsepower, thats kinda expected.....

I'll see what mpg figures I'll get over few days. Will keep you posted.

revstriker

This is what I think too, although I question where it gets the Avg. MPG from. It could be from the after start, or after reset, or from somewhere unseen. I'm pretty sure my car reads about 405 after fill up too.

Lynn

My uneducated opinion is that the range calculation doesn't use average MPG, but rather uses instantaneous MPG based on fuel flow. Acutally instataneous probably isn't right, more like a smoothed average of a number of fuel flow reading over a short period of time.

tommy

Unfortunately, I'd have to agree with Lynn. My driving range has gone from 10 miles in a bottleneck to 20-40 miles once the highway gets started again, and that's too much of a gap in the range to be explained by overall mpg, which wouldn't have been affected that much by a 10-minute bumper-to-bumper situation.

dswildfire

yeah, 405 is the default setting that it gets reset to. but it does change with your mileage. last night driving home from alta loma to encino, about 60 miles, i managed a top mileage of 42.7 mpg, at which point my range indicator said 585 miles, but as i got closer to home and altitude changed, my mileage started dropping and stuck aroun 35 mpg, at which point the range indicator said something like 420 or 430 miles left.

trench

I agree with both of you tommy and Lynn - I think that somehow the car meters the fuel flow to calculate the current gas mileage at the time, considering how the car updates the mileage every few seconds. The float reading probably isn't super-accurate the car just guess how far the range is from the rough reading from the tank combined with the fuel flow (which it should know with higher accuracy); I'm sure the system is designed to err on the side of caution. I've also noticed that if the MPG is calculated via miles traveled since fill-up vs. gallons added that it is usually slightly off what the car thinks the mileage was over the same distance.

Cheers, BT

MB-BOB

...you bet, I've driven my sedan 5-miles after the range gauge said "0" and still made it to my fav gas station...

I don't mind parking my Benz on the side of the road and thumbin' for a ride! :o :o :o

revstriker

Or you could press your button to activate your $260 tele-aid.

MB-BOB

You mean press the button labelled, "See, you should've renewed your Tele-Aid!"

WebGuyNJ

On Mondays or fridays when I fill up with around 420 miles on the tank. Its says 405 after refill. Usually by the time I get home the projection is 460.