Checked my MPG...now what to blame? 300SDL
 

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!:eek: 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..)

What's the 0-60 time.

What's the maximum boost level?

How long have you had the car?

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.

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.

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

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...

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.

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.

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?

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) :D

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.

OMG! THIS IS MOST LIKELY WHY!!!!
 

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?

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.

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.

And what is this anti-seize? Is that a brand name? Can I buy it at Walmart?

Pretty much any auto parts house will have it. Not sure about Wally World.

Permatex, CRC and others make it. Ask for it at the parts store and they will point you in the right direction. That is an important step that often gets skipped when putting steel parts into aluminum components.

Good job on the coolant! That is what I used. CarQuest carries it down here. Be sure you get all that green crap out. I just replaced my radiator this week and did the same. It was a little time consuming doing the flush, then flushing with fresh water, back flushing everything and un-hooking and re-hooking hoses. I also flushed with the thermostat out so it would not take as long (waiting for it to open). But, I think it was worth it.

And, THIS is why I do all my own work - I don't let "mechanics" touch my cars. What an idiot. *sigh* But no, AutoZone won't sell Wahler or Behr t-stats. You'll need to buy one from the dealer, an internet MB parts vendor, or a local European parts supplier. Bummer, dude.

Anyway - I seriously doubt this is the cause of your 19mpg. My first thought is also an intermittent odometer. That's tough to spot unless you're watching it all the time, or unless you can go on a long trip and compare to the interstate mile markers over several hundred miles. 19mpg is too low for an SDL. Replace the air filter and both fuel filters if they are not recent. Jack up the car and spin the wheels by hand to check for brake drag... front wheels should spin easily and keep rotating for a few turns. Also check for any fuel leaks. You should be getting at least 22-24mpg or so around town, and on the freeway, at least 24-28mpg. I assume power production is normal? 0-60 time is good at around 13 seconds? If not, you've got other problems...

Be careful with anti-seize... do NOT use a torque wrench, and normal torque specs, on fasteners with anti-seize applied. Otherwise you'll end up learning about Heli-coils and Timeserts. Anti-seize is great stuff when used correctly though. You don't need it everywhere. IR thermometers don't read properly on shiny surfaces such as aluminum (they read lower than actual), so be careful if you're using one of those.

BTW - don't forget to update your "low temp" thread with the holed t-stat photos.


:euro:

Do those GPS devices track your mileage as well? I'm a pretty ok navigator and didn't really NEED a GPS...BUT Tracking accurate mileage with a navigation system sounds cool. I never really looked into it.

ON another note, I had my brakes done prior to this whole thermostat meltdown. And I was getting the right MPG during the last days of May and the first of June. After I received my car from the mechanic (After thermostat housing bolt dilemma), I still clocked 23 MPG after filling up. Then on June 25, I clocked 18.80.

After you replace the t-stat, make sure none of the brakes are dragging, as I mentioned earlier... it's suspicious that this started soon after the brake job.

:nuke:

So I'm on my way to checking the brakes...

BUT! No boost? You mean to say that if I don't get a turbo boost, my MPG suffers? I'll check out the vacuum lines and report back...

Check out these videos and tell me what you guys think

http://www.youtube.com/watch?v=djvjj8tRDhE

http://www.youtube.com/watch?v=X2OmksyJwys

I could be wrong, but I think a little bit of brake pad noise is acceptable. The wheels are heavy and won't spin very much in general. Especially if you just replaced the brakes..the pads might take a few days to wear in. The rotation seems ok to me, but I'll let someone with more experience have their say over mine!

As for boost, your mpg shouldn't suffer too much. I went without it for a few months and my mpg was basically the same that it is now. However, if you want to go fast, you might use more pedal for a longer period of time since your power will be down, and this could theoretically reduce mileage. Having the boost will also increase the fuel the engine gets, but you'll get more power so you won't have to use as much pedal.

Incorrect fan?
 

You mentioned that you did some modifications to your clutch fan and fan. If you used the wrong fan or clutch, you could be over cooling your radiator. If the fan is always engaged the engine has to work harder to supply power to the fan. If the engine is working harder, it's consuming more fuel. Dave.

Looks pretty normal... there's a bit more drag than optimal, but nothing to cause a drop to 19mpg. The noise is nothing to worry about, probably just the new pads haven't fully set in yet. If you had any serious drag, the wheel wouldn't spin with your finger. Don't forget to check the passenger side too, btw...

Oh yeah - you ever check the 0-60 time with a stopwatch?


:beer:

The quest continues...to find better MPG
 

Greetings fellow MB lovers! I bring to you an update on what I've done so far.

-I've removed what's on the left of the vacuum pump
-Put in 80C Dealer thermostat
-Checked and reaffirmed for brake drag (seen in the videos)
-MOST RECENT (As of July 3 2009 at 0700) done a 0-60 in what I think is 13s. It's weird because I tweaked my ALDA and yet it's still 13s....hmmmm

Check out my youtube video of my 0-60 time and tell me what you think!

http://www.youtube.com/watch?v=D8C77oO_DpE

I believe I'm gaining MPG back. At the half mark, it's about 20 - 21. Better than 18.80...

A question! You know that thing on top of the overboost protection? the one that's connected to the ALDA and the intake manifold? Is that an adjustment to add more boost?

The 0-60 time seems normal - power output should be ok.



20-21 is still pretty bad. :(



Not sure what thing you're referring to, but if it's a little box with 3 hose fittings and 2 hoses connected, it's the overboost protection solenoid. It kills the boost signal to the ALDA when boost pressure is too high. It's not an adjustmen to add more boost. Adding more boost does not increase power, it just overheats the intake air. You need more fuel to make more power.


:nuke:

pull the wheel and see if the rotor is grooved, otherwise, it's perfectly normal to have that drag. BTW, all thermostadts are about the same. Don't knock yourself out trying to find a behr or whatever. Delco, Ford(Fomoco) , napa, etc, will do the same job if it's the correct diameter and got the same opening specs.
This is a great source of information on this site. Enjoy it and your car.