I have a 99 with close to 150k miles. runs great. Super fast and strong, no smoke unless I mash on it. I have had it a bout a year and and have always thought the mileage was subpar. I get 300-350 gal on a tank. I avereage out the last 4 tanks and with mostly stop and go LA traffic, with a little open freeway here and there, I got an average of 18mpg.

I have recently changed the oil and trans oil + the fuel and air filters. I have also replaced all of the fuel deliver lines.

What else can be going on?

My best guess is that it has to do with another thread I am going to post later this week, but I'll put a bit of that here maybe it will help.

From the day I got the car I always thought the rear end was loud. I bought it with bald back tires, so I went out and replaced all 4. In 6 months my rear tires were down to threads ( I drive the car pretty nice and do not burn out or put on high miles). Since I bought the tires used I figured I must have been ripped off and not paid attention to the thread depth. I put another set on the back and now 5 months later they are almost bald. I have seen evidence of some sort of repair work to the trunk, so I am thinking it has been in a wreck. And I am now thinking that the rear end is not straight. The tires are work evenly, so it's not camber or toe, but I think if the whole axle were tweaked sideways that would give me the noise, the tire eating and most likely enough drag to cause the bad mileage?

Do I have this checked at a body shop or an alignment place?

Thanks for ANY input.

- Dylan

18mpg is really low.


Have you had the car alighned? If not bring it to the dealer and see what they say, sounds like you have some rear end issues which I doubt are helping.

Other than that check the usual stuff; make sure the tire pressure is right, the brakes are not dragging, you don't carry a ton of crap in the car, etc.

Take a look at the plastic lines on the IP and make sure they are not leaking.

If all else fails I would have the injectors tested and time it.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

18mpg is more likely a fuel leak.

What rpm is the engine turning at 60mph?

Sixto
87 300D

And I thought 25mpg average was low for mine...

I agree, sounds like a fuel leak. Does your garage smell like diesel/biodiesel?
In any case I'd have the alignment checked out.

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99 E300 TD -- sold
01 540i 6 spd

Cars with independent rear suspension have to have the rear aligned as well as the front, and the rear has to be properly set up before you can properly do the front.

I doubt that the fuel economy problem is related, sounds like two separate problems. Our '96 has averaged about 26 MPG since we've had it, mostly driven around town.

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

I had a similar experience when the ULSD changeover happened - big fuel leak from the delivery valve seals. I am assuming that you have not noticed a puddle of fuel under the car - try taking off the rear 'belly pan' and look for a nice shiny coating of diesel fuel on the heat shields.

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Scott C.

2006 E320 CDI (120k miles)
FOR SALE: 1998 E300 Turbo Diesel - Black w/Tan Leather - Euro delivery (236k miles)

I agree with the others that it is hard to imagine an aligment issue causing this though going through tires like you are you should have it aligned. If you had a brake dragging you surely would have noticed it by now I would think, but you might just check to see the car rolls OK and that each wheel is turning freely. I would also have to conclude you have a fuel problem somewhere, either a severe leak (most probable) or something else going on in the fuel system.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Hmmm - fuel huh? I did have a leak at right after I bought it, I fixed that and had the all the clear little fuel lines replaced. This was literally my first tank of fuel. I guess he could have done something wrong when putting it back together, but since then I have had great performance, and no diesel smell (other than from the tail pipe at idle).

The car does leak oil a bit, this is from the IP and I planned on (finally) getting that fixed next week. It's possible that this is not oil but fuel...

Is there any kind of diagnostic tool that can hook up to tell me anything? The only major work I have had done was to remove the IP, replace an o-ring, and reinstall it - they timed the engine when they did that.

I get about 300 miles on the odometer before the fuel light, what are you guys getting?

My reserve light goes off at ~580-600 miles. I drive 110 miles a day; 20 of that is slow and go.

You are in heavy stop and go traffic so your mileage will differ.

Usually a leak at the IP is fuel; although could be oil.

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Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)

580-600? I have been driving this car for 13 months and the only time I see over 350 is I took a LONG trip on the freeway. Wow, if I could be in the 500's that would change everything.

The IP leak is not where it connects to the block, but on the back of it (I already fixed the one between the IP and the block). The mechanic showed me where the leak was, and said the could probably get to it from underneath on a rack, with out removing the intake up top. If this was a fuel leak ( it might be, the spots are not very "thick" and I never seem to run low on oil, but it is pretty black) then things would start to really make sense.

I'm getting my alignment done in the morning and I'll try and get the leak done this week. Ohhh that would be sooooo coool.

IP Timing can be the cause...I'd be looking at that. If they removed the IP and didn't time it correctly when it was reinstalled that might be it.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

It got the same mileage before and after the IP removal - it was done at Mr. MB here in LA, a very highly rated shop. If anyone can set the timing right I trust it's him.

Also, power is good, and there is only smoke if I floor it, and even then there is not much. If the timing was bad, wouldn't I lose power and gain smoke?

Let's start with some basics...are you running stock tires/wheels on the car or some odd oversized ones? Have you ever checked the accuracy of the odometer and speedometer?

It is really hard to fathom getting 18 MPG. The absolute worst I ever saw was about 22-23 MPG in the dead of winter right after I bought the car and before I did any work on it or blew the crap out of the engine. Now I never see less than 26 in winter and average darn near 30 in summer with mixed driving. Straight highway driving at 65-70 will get me 32. Yours has something seriously wrong with it, ask your mechanic why it is getting such poor mileage...if he is so good he ought to be able to find the problem!

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

The car does have 18' AMG wheels and SportPilot tires on it. Yes these will throw the odometer off, but not by the scale we are talking about here.

As you state, something is very wrong. I will redo my mileage calculations maybe I messed something up. I can tell you that in pure city driving I get an average of 300 miles before low fuel light comes on.