1998 E300TD Low Mileage Problem - PeachParts Mercedes-Benz Forum

jayres · #1 05-06-2008, 11:00 PM

1998 E300 TD w/129k Averaged 30 mpg for the last 10k miles. Changed the fuel lines to 10mm plastic and viton, added coolant heat exchanger to heat fuel and mileage dropped to 21 mpg. Just finished installing Elsbett kit with second filter and proper re-routing of fuel lines and mileage has stayed around 20-21 no matter how I drive. 250 mile trip last weekend with extended freeway driving netted 22 mpg.
Just replaced water pump/thermostat (broken impeller) and radiator. Car has all viton fuel lines and no leaks anywhere. Engine is dry. New air filter. New synthetic (Amsoil) oil and filter. New MB coolant. New drive belt. Just ran two tanks of straight WVO and mileage is still 21 mpg.

Meanwhile throughout all of this the power of the car has been Oustanding! Extremely fast and powerful easily outrunning most cars on the road. In fact the power output has increased while the mpg has dropped.

Help!

ramtony · #2 05-07-2008, 11:01 PM

same thing happen to my 99 e300 152k miles after i change the fuel return lines, no one here thinks that fuel return lines have anything to do with fuel economy and at first i didn't either, but now the return lines is the only thing i can think off.

by the way what kind of kit do you run your wvo with?, ith diesel at 4.15 i'm thinking of converting my car to wvo

TMAllison · #3 05-07-2008, 11:36 PM

21 mpg in 1998 E300TD HELP!

If you are leaking at the return lines i can understand a reduction in economy. There is a LOT of fuel not being used and flowing through those lines.

If you've ever done a DP you'll understand how much extra fuel the IP is provided. A similar overage is sent to the inj's.

jayres · #4 05-08-2008, 12:01 AM

I replaced all but two fuel lines with new Viton lines and at the same time replaced all of the o-rings with Viton o-rings. I had the injectors sonically cleaned and recalibrated to 5 bar higher than stock, per Elsbett instructions.
Since I have meticulously done all of the work slowly over a 3 month time-frame, I have carefully watched the results of each change. I have never had any fuel leaks at any time anywhere. The entire car is dry as sand, front to rear.
I am just searching for something that I might have missed that would so drastically decrease the mileage which seems to be still dropping. Drove 80 miles today in gridlock freeway to high speed to in-town and car not only runs flawlessly, it absolutely screams with performance and outruns most anything off of the line. Just totally high fuel consumption.
My next step would be to return the fuel routing to stock and see if the mileage returns.

TMAllison · #5 05-08-2008, 01:21 AM

Quote:

Originally Posted by jayres

it absolutely screams with performance and outruns most anything off of the line.

What ARE you using for fuel?

I drive 110 miles a day on D2 mostly and sometimes B99. Its 80mi at 75-80mph and 30 mi at 5-15mph. I get 30-31mpg consistently on D2 and 27ish on B99. I don't get on it too much unless I need to smoke out a tail gaiter. My turbo does come on a LOT more burning B99 compared to D2 even during normal acceleration.

My guess is you are enamored with your turbo in city driving, are doing a lot more slow and go than I do, and are using a fuel type that provides less energy than what the fuel system was designed for.......you could always put it back to stock and see what happens.

P.E.Haiges · #6 05-08-2008, 05:38 AM

The old rule still holds true: "If it ain't broke, don't fix it".

P E H

KarTek · #7 05-08-2008, 06:44 AM

My gut tells me that I wouldn't be heating regular Diesel fuel, only VO. My GF's Golf actually has a fuel cooler. This is just me guessing though... Doesn't heating fuel lower it's energy density?

LUVMBDiesels · #8 05-08-2008, 08:05 AM

was the 10k miles also done on WVO? Remember that with WVO there are no standards and you could be running some particularly weak oil.
If your mpg went down when you switched from D2 to VO, I can understand the drop.

Hatterasguy · #9 05-08-2008, 10:59 AM

Revert it back to stock and see what it does. You can't fix a problem on a modified car, there is no way to know if its the car our your mods.

P.E.Haiges · #10 05-08-2008, 11:00 PM

KarTec,

I never heard of fuel cooler. How does it work?

P E H

KarTek · #11 05-09-2008, 05:42 AM

It just looks like a heat sink inline with the return fuel line and mounted under the car. I think I've read somewhere about people buying them and putting them on other diesels for a small gain in power but don't quote me on it...

It's really for engines that run the fuel through the head to unit injectors to keep the fuel down to a reasonable temp.

uberwgn · #12 05-09-2008, 07:20 AM

Quote:

Originally Posted by P.E.Haiges

KarTec,

I never heard of fuel cooler. How does it work?

It looks similar to a transmission cooler on an American car. The fuel coolers are only fitted to VW TDis equipped with automatic transmissions.

frankstallone · #13 05-09-2008, 07:47 AM

Quote:

Originally Posted by KarTek

My gut tells me that I wouldn't be heating regular Diesel fuel, only VO. My GF's Golf actually has a fuel cooler. This is just me guessing though... Doesn't heating fuel lower it's energy density?

What year did the VW Golf come with a gas cooler? I have never heard of that.