What is the best MPG to expect out of a w123 300 turbo Wagon? - PeachParts Mercedes-Benz Forum

MercedesOtto · #1 11-10-2008, 10:35 PM

My 300TD wagon only gets 20MPG . Is anything wrong or is that all I can expect. What could be wrong?
How about MPG on the 240D and 300D. How much better will it get having a manual transmission? It is a great car with only 174.000 Miles and new transmission but with the diesel cost I may have to let it go.

MTUpower · #2 11-10-2008, 10:40 PM

23-28 is average combined.

Chad300tdt · #3 11-10-2008, 10:49 PM

Quote:

Originally Posted by MTUpower

23-28 is average combined.

My wagon runs great and only gets 22 mpg, plus the AC doesn't work. I do mostly city driving though.

Maybe I should take off the AC belt until I get around to fixing it.

leathermang · #4 11-10-2008, 10:49 PM

When did you set the valves , check the timing... that sort of stuff ? Changed the air filter ?

#5 11-10-2008, 10:54 PM

Quote:

Originally Posted by Chad300tdt

Maybe I should take off the AC belt until I get around to fixing it.

There is no point, the clutch takes no power to spin when not engaged.

MTU got it, 23-28 is average combined. Maybe up to 30-32mpg with highway-only driving in ideal conditions (flat, no wind, 55mph cruise and vehicle/engine properly maintained). Claims of 35+mpg on eBay and craigslist are straight lies.

Chad300tdt · #6 11-10-2008, 11:00 PM

Quote:

Originally Posted by ForcedInduction

There is no point, the clutch takes no power to spin when not engaged.

One possibility ruled out.

Oh well ... I'm ok with 22 mpg anyway.

kerry · #7 11-10-2008, 11:10 PM

23-24mpg. Are you sure your odometer is not sticking?

t walgamuth · #8 11-10-2008, 11:20 PM

Quote:

Originally Posted by kerry

23-24mpg. Are you sure your odometer is not sticking?

This is what I would expect. 30 mpg might be possible on a test track at a constant 50 mph, not likely on the actual road, except possibly at high altitudes.

barry123400 · #9 11-11-2008, 12:02 AM

There are many reasons for sub standard milage. Most them are reasonably cost effective to check out. Basically develop a list for yourself to systematically check out. It is basically a tune up type of deal with a few things thrown in.

I can only suggest what I would do if I had a 300d turbo producing say 20 mpg on the highway.

Make absolutly sure the odometer is not hanging up first. Not uncommon. As already pointed out on this thread.

Check for fuel leaks and fix any found.
Make pretty sure a stream of air bubbles are not being processed through the primary filter.
Do a compression check.
Check fuel feed pressure at the injection pump with a gauge.
Check drip timing on injection pump and chain stretch. Check fuel pressure before doing the drip test. They interact to some extent. If the fuel pressure is far too low I think effectivly the pump is still retarded after the drip test.
Check valve clearances. Before the compression check or if any very tight valves with no clearance are found do it before and after adjusting the valves. You want to know what the cause of the low fuel milage was.
Pull injectors and have them checked.
Make sure air filter is pretty good.
Before any of the above verify brakes are not dragging and tires are at a reasonable pressure.

If all these tests do not uneath the problem consider a cheap injection pump from a pick and pull yard. You can stop the testing at any stage the problem is found of course. The injection pump is not totally speculative if all the above is covered first. The pump should be really cheap as there is not a positive certanty the old one is bad just a suspicion it might be at that point. Never pull a dry pump always one with fuel still in it. Just less risk.

turbobenz · #10 11-11-2008, 12:59 AM

Wagon should get slightly better mpg than a sedan

#11 11-11-2008, 01:07 AM

Quote:

Originally Posted by turbobenz

Wagon should get slightly better mpg than a sedan

From slightly better aerodynamics, yes. The extra 400lbs offsets some of that though.

turbobenz · #12 11-11-2008, 01:30 AM

Quote:

Originally Posted by ForcedInduction

From slightly better aerodynamics, yes. The extra 400lbs offsets some of that though.

true, highway should be a little better though, unless the extra weight is causing that much rolling resistance

Biodiesel300TD · #13 11-11-2008, 01:30 AM

In the 4 years I've owned my wagon the best milage I have gotten is 28 mpg. I pretty regularly get between 24-26mpg. I wouldn't expect the 300 sedans to do a whole lot better, maybe a mile or two better. The 240 manuals get the best, followed by the 240 autos. 20 mpg is too low. Some things to check would be:

1. Valve adjustment
2. Air filter
3. Tire pressure
4. Dragging brakes/Dragging e-brake
5. Fuel filters

MBeige · #14 11-11-2008, 01:43 AM

22mpg sounds a bit low. Check that the throttle linkage is up to spec. FWIW I got 22mpg and found out that the 10mm screw that holds two of the linkages together was loose. Tightened it and power came back, as well as better mpg. I kept flooring it just to get it going.

My lowest was 23mpg with A/C use and heavy city driving, and best at 29mpg with mostly highway driving and no A/C use (mostly at 75mph).

JimmyL · #15 11-11-2008, 01:45 AM

On the '85 I am usually in the 22-25 mpg range with AC being used. The best ever is 28 but that hasn't happened since about the first month I've owned it.
I haven't burned through the first tank in the '81 yet, but it started to dive down towards E {or is that R} much faster than I had hoped....