Checked my MPG...now what to blame? 300SDL - PeachParts Mercedes-Benz Forum

Abadjay · #1 06-26-2009, 01:18 AM

Well I filled up tonight at a station in Panorama City CA. While filling up I was looking at my fuel gauge and it read below half...funny cuz I only traveled 238.5 miles. After 12.686 gallons...my MPG was 18.80.... WOW!

I average about 22.5 MPG

Vehicle: 1987 300SDL Turbo OM603

I thought I divided wrong...but I did it again...

So now I have these things in mind:

-> Turn the ALDA back 1/2 turn (after 2 full turns CCW. See below*)
-> Change the Thermostat (See below**)
-> And of course the smaller things like no AC and less "flooring it"
-> I used to fill up my tank up to where I see the fuel sit on the neck (almost overflowing within a cup or so)...maybe I should stop doing that?
-> I doubt that there are any leaks in the system. I don't see patches of fuel on my driveway...so that's what I'm basin it on

(*I don't see much smoke, but I feel that I could turn back the ALDA some...good performance though =P)
(*3/4 of driving time spend under 80C and never higher unless ambient temperature is hot. I'm thinking that this is the main reason)

Tomorrow I'm off to Universal Studios, but I'm sure this won't leave my mind knowing I get low MPG...I might as well get an SUV...(I don't want to...but..sigh..)

Brian Carlton · #2 06-26-2009, 08:33 AM

What's the 0-60 time.

What's the maximum boost level?

snookwhaler · #3 06-26-2009, 08:39 AM

How long have you had the car?

What is your odometer error (if any) against a measured mile? (not speedometer error)

Brian Carlton · #4 06-26-2009, 08:52 AM

Quote:

Originally Posted by snookwhaler

What is your odometer error (if any) against a measured mile? (not speedometer error)

X2.

The odometer failure will present itself by slipping...........resulting in lower miles on the gauge than actually traveled.

awsrock · #5 06-26-2009, 08:54 AM

Check what Brian recommends; this way we will know if it could be a timing issue, no boost situation, etc. It would also help to confirm your odometer is accurate. In addition to these, however:

The ALDA shouldn't make much difference, unless you are really in the pedal all the time...but, with it turned up, you should theoretically need to use less pedal to do the same work.

I'd bet that your thermostat is one of, if not the, culprit. You should definately be up just over 80c..Mine warms up withing about 1-2 miles in the summer.

Another thing to consider, in addition to the thermostat, is that the fuel pump you went to may have "ripped you off"..I usually go to the same pump, but last fill up I went to a different one, and somehow got about 2 mpg less that I should have...the tank was reading just shy of 12 gallons, but somehow I managed to fill it up with 13.8..hmm. I know that the guages aren't the most accurate, but the whole time I was pretty darn sure that I was getting much better than what I got. oh well. Since then, I've been going to my usual pump and things have been fine.

pawoSD · #6 06-26-2009, 10:01 AM

Dragging brake caliper or parking brake perhaps? Its got to be either that or a slipping odometer simply not reading the miles.

Abadjay · #7 06-27-2009, 02:26 AM

Well I did get new rear brake pads...but I don't feel the car dragging...it FEELS fine...but as far as I know (and it's not a lot) it shouldn't be brakes...

Any good place to get a GOOD WORKING Thermostat? The one I have is rated at 80C Behr. But I guess I'll look elsewhere.

I hope to dear lord the odometer isn't slipping...I would keep my eye on it all times...but you know....How to check?

It currently (whether it be false or not) has 188,333 miles. So far since I filled up, it has 57.1 miles and the needle has already moved a lot (Not normal for me). The mileage traveled makes sense though. I calculated my traveled distance on Google Maps from the point of filling up to when I back home just 1 hour ago and it makes sense sense. The Odom reads 57.1 and the goggle maps is 56.4

I'd contribute the other 0.7 miles toward finding parking at the theme park and parking in Hollywood etc.

At least since last night, I'm confident that it's not odometer slipping...

t walgamuth · #8 06-27-2009, 09:18 AM

The behr stat is a fine stat. 80 is the right one too, as long as its functioning correctly. Since they are fairly expensive I would test it before simply replacing it.

snookwhaler · #9 06-27-2009, 09:43 AM

Quote:

Originally Posted by Abadjay

I hope to dear lord the odometer isn't slipping...I would keep my eye on it all times...but you know....How to check?

The only way to really know is to use a GPS that has an odometer function or find a road that has mile markers and check your odometer against that "measured mile".

I found mine to be off by 20% and my odometer is not slipping. I pulled it and inspected it just to be sure. I think that my cluster is out of a car with a different rear end. Or maybe just because my tires are 1 size over. Putting new tires on the car can cause errors too (tires of a slightly different circumference).

IE: I thought I was only getting 21 to 23 MPG. But my corrected/actual mileage is 26 to 27 MPG.

If you already ruled it out then don't worry about it. This is something that is easily overlooked. Now, if you have owned your car for a year or 2 and you KNOW what the mileage should be after many tanks.... Then I could see your concern and would be looking elsewhere for the cause. That is why I asked "how long have you had the car" in the above post.

Abadjay · #10 06-27-2009, 11:15 AM

Quote:

Originally Posted by snookwhaler

If you already ruled it out then don't worry about it. This is something that is easily overlooked. Now, if you have owned your car for a year or 2 and you KNOW what the mileage should be after many tanks.... Then I could see your concern and would be looking elsewhere for the cause. That is why I asked "how long have you had the car" in the above post.

Nice car by the way!

Anyway, yeah I had the car for 2 years this September. I'm pretty sure that I know my distance traveled does not equal the Diesel used up. I'm really having issues with getting up to 80C. It sucks because I bought this Thermostat from Performance Products and I trusted them with their stuff. Now I did cooling system modifications back in earlier June which involved fan clutch and fan blade change as well as water and thermostat...

What I have now in mind is this:

-The water is wrong or has the wrong proportion of distilled and coolant
-The Thermostat is inverted
-Put in the OLD AND RUSTY thermostat that works more correctly.
-I also had this in mind...after my bolt was broken I took it to the mechanics. He put in the wrong water {green} in my system...so I have to flush it out. Could the wrong water be it?

pawoSD · #11 06-27-2009, 01:15 PM

I occasionally compare my odometer and trip meter to the mile markers on the freeway, so far they've all been dead on. (except my dad's with the diff swap, his is about 10% off)

Jeremy5848 · #12 06-27-2009, 01:58 PM

Quote:

Originally Posted by Brian Carlton

X2.

The odometer failure will present itself by slipping...........resulting in lower miles on the gauge than actually traveled.

X3 . . . that's exactly the problem I had with my '87 300D. The odometer would work fine for awhile and then simply stop turning. Speedo was fine. After awhile the odometer would start working again. Confirmed the error with a GPS, about 20% low miles recorded. Pulled the speedo, had the odometer rebuilt and no problems since.

Abadjay · #13 06-27-2009, 02:00 PM

I HAVE FOUND A BIG REASON WHY!!!!

As you know, I have had my thermostat housing bolt stuck...and I had my mechanic finish my "DIY" (that I obviously couldn't finish...)

So he fixed everything....or so I thought...

HE DRILLED HOLES IN THE THERMOSTAT!!!! (SEE PICTURES)

ARGH! I don't know what to say or tell him, but he's been my trusted mechanic for years. Now I believe my thermostat was good to begin with! It just now has 5 (count 'em) 5 HOLES!

Does Autozone sell the Behr ones?

snookwhaler · #14 06-27-2009, 02:36 PM

I'm not real familiar with that platform (W126 and 603). But, I would think that you would want at least 80C and a little above to get maximum mileage. Drilling holes in the thermostat would slow down your warm up times and allow more flow when the stat is fully opened allowing more cooling.

I'm thinking that if you were having problems getting to 80C, drilling holes in the thermostat was the wrong thing to do.

I think you should replace that thing with the correct one (w/no holes in it), fill it up with the right coolant and distilled water and see what you got.

Also, find someone that has one of those laser temp. gauges and shoot the thermostat housing after a 20 minute drive and compare that reading to what is indicated on your temp. gauge.

There could be other factors involved as well. But it seems that "where you are at now"... This is where to start.

Edit: Be sure to use anti-seize on the thermostat bolts when you put them back in there. When I did mine they made a "pop" sound because the last person did not use anti-seize. They were covered in corrosion when I got them out. I got lucky and they came out OK.

Abadjay · #15 06-27-2009, 03:57 PM

Quote:

Originally Posted by snookwhaler

I'm thinking that if you were having problems getting to 80C, drilling holes in the thermostat was the wrong thing to do.

I think that goes without saying

But I found it drilled from the mechanic. I didn't tell him to drill ANY HOLES! I didn't even think of drilling holes. BUT! Hypothetically(!), if I were to drill holes, I wouldn't start with 5 holes...

I was expecting to see my new thermostat fresh with no holes, but he drilled 5.

Currently I'm flushing the old remnants of the green coolant with distilled water. I'm preparing to put the good ol' Zerex G05.