Om606 TERRIBLE MPG
 

My car runs perfectly fine but I’m getting 22mpg 70% highway 30% city. Awful. 215k, I have original injectors. Probably time to send them to greazzer when I get a chance, but can’t imagine worn nozzles would cause such terrible mpg. My compression is great, I tested it before when I did glow plugs out of curiosity. Doubt timing chain stretch is a thing since it’s had Mobil 1 synthetic oil changes since new (family owned since day 1 and maintained) at 5k intervals.

Any ideas? My tire pressure is set all even. It’s literally a waste of money in fuel. I don’t drive over 75 which is about 2700rpms.

I’m also calculating the fuel from about a little above half a tank to right before the reserve light comes on I fill it up to get back to where I was with $30. I calculate the miles travel by the gallons to refill to the previous spot my fuel gauge was at. Wonder if that skews my results by not adding a full tank?

Also I have minimal smoke if any. I’ve gotten as low as 18mpg doing the same traveling. It’s despicable.

I am guessing that you would do better filling it all the way up. Check over three or four tanksful for a more accurate estimate of mileage. For example fill it up, punch the mileage to zero and drive three hundred miles. Fill it up and repeat. Calc mileage each time.

The part where you're trusting a VDO gauge and sender to actually have half a tank of fuel when they say they do is your main issue.

Fill it all the way up, run it down, fill it all the way up, then divide it out. Guessing from spots on a gauge will never work. I've tried it myself and either I'm getting 16mpg or 60mpg, it never works.

You need to measure your fuel consumption more accurately before jumping to any conclusions

I try the same, but run it down to a quarter tank and then fill with 5.25 gals(tank holds 21 so divide by 4). Then use your mileage when it drops back to a quarter tank. The fuel gauge is wonky and 'appears' to fall faster between the hash marks than when its close.

Depending on city/highway ratio I can get 550-600+ per tank or about 26-28. Not the 30+ touted by others and in the for sale listings, but hey for a 19+ year old car not bad.

Mileage sounds about normal to me.

You get apparent great gas mileage on the first quarter tank because you have to burn enough gas for the level to drop below the float before it even registers. The float cannot move if it is buoyed against the top of the tank by gas (or diesel fuel).

Not bad at all. Gonna try the tips everyone mentioned and fill it up to the top and see.

Pretty awful for the 606 if it is the case. About right for the 617 maybe. My 603 got 28 highway.

Yeah, I was thinking about the 617.

You cannot measure fuel economy accurately unless you start with a fill up, the drive til it is lowish, keeping track of your miles traveled, then fill it again and divide the mileage by the gallons traveled.

It's winter.

You really need several tankfuls accurately measured and from the same pump to draw any sort of conclusion. As it stands, you simply don’t have enough data. For what it’s worth, my 98 got 26.5 miles per gallon over the course of 12,000 miles… If I were just measuring using winter diesel, I would expect around 23 or 24.

Winter diesel is a couple few mpg less. I get 27-29 MPG summer diesel and about 25 winter diesel with my 617.

Cat might be clogged. Take the down pipe off and blow a shop vac (in leaf blower mode) to see how well it’s flowing.

Mine got about 21-22 in city driving and 27-28 highway.

If you do all of the above, and still confirm very low mileage, check that your thermostat is not stuck open. I had one stick open on my CDI and mileage dropped to 17 confirmed over 400 miles. The temp never reached 60C. Diesels like to run hot (or at least NOT cold).

And how long does our guy let the car warm up? Idle = 0 MPG

I have a Chrysler product with an average MPG display, in winter the MPG drops 3 MPG running the same route vs middle of summer. I don't let the car warm up more than 30 seconds or so in the winter.

Snow increases tire to road drag, tire pressure drops causing more tire drag, oils are thicker causing more drag , engine takes longer to warm up , rear defroster takes electricity ( though this is somewhat offset by the rad fan running less ) , heater blower might be running longer / higher speed taking more electricity, maybe more time sitting in traffic due to road conditions.

Same thing happens with my 606 at 91.000 miles. Summer or winter - it makes no difference, I get 8,5L/100km at 70mph on tempomat while other owners report 6,5.
Everything seem to work fine on the car.

Look under intake manifold and see if there are any leaks.

I vote winter blend fuel 1st.... then see if any leaks

99 e300td- gets around 30 mpg... Only driven in summers -92k miles

my 05 cdi-- 31 mpg winter... 34 mpg summer-- 39 mpg all hgwy

87 sdl-- 29 mpg Only summer...

No leaks, when I put new orings I also replaced the rubber fuel lines. Everything is dry.
I drove it across Europe and fueled in many places. Last summer it wasn’t doing any better. I bought it with 82k on the clock

I might pull the injectors and have them checked. Standard Mercedes maintenance at 100 thousand miles. Cat deterioration as mentioned I think was a good thought. Anyway to check them other than as mentioned?

Air filter, alignment, tire pressure, outside temperatures, speed will all make a difference. For winter a big factor on the highway is that the air is more dense so it requires more energy to move it. Do you give it the old Italian tune up and go full throttle to high rpm? That helps too.

Diesels can't run rich like a gasser can so if you are not being followed by a plume of smoke you are burning the fuel injected properly. Squirting injectors, dragging brakes, plugged air filter, etc. etc. can hurt mileage a bit but only on the margin. I typically get about 23 in normal driving and about 30 on a trip in my non-turbo 606 which is geared down to make up for it's low power. Make sure you don't have a major fuel leak that you are not noticing. I suspect your mpg calculation technique is your problem.

I would like to "check" the cat by removing it if it's going to make a difference. I don't have an injector pop tester and the original one is not cheap. I should send them to a workshop...

I fitted a new air filter just in case a while ago, nothing changed. I use 4 new Michelin Alpin 6. Sometimes I kick it a little but I don't think it was more than 100mph+

There is no smoke behind this car no matter how I drive it. It rolls fine if I put it in neutral before a red light and calipers are "cold" (I can touch them). Before I left Romania for UK car was lifted and I removed the shields in order to check its overall condition. Apart from the shaft drive bearing - the rubber is a bit tired all is nice and clean. I record the miles/liters when I fill the tank. In almost 10k I had time to check this several times.

News: I bought the parts and fitted the EGR defeat system. Car feels more responsive, I wonder how the mileage will be influenced. Still no smoke.