20 mpg...this is not right...I need help!
 

20 mpg...this is not right...I need help!
I just purchased a 1981 300D (non turbo) with 255+++ miles. Engine still runs strong but my only complain is...how come I am only getting 18 to 20 miles/g. I've had an 84 300D TURBO, a 190D 2.3 and they were great on fuel...30 to 35 mpg. I have purged it already and it made a noticeable difference. I NEED HELP FROM YOU GUYS BADLY. I am a gas engine technicain so I am lost..................... S.O.S.!
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Thats all I've been getting on recent fillups. But, I must admit I drive in "S" most of the time (third gear) and my foot, is actually a solid, pure, shiny block of lead, not a human foot. :D ;) Lately I've been smelling a diesel fuel smell drifting from yon-back area of my car when I get out, perhaps that could be why I am getting 20ish most of the time....I think the little rubber hoses that come out of the tank are oozing. I'll have to back up some ramps soon and find out....

You'll need to drive the car though several tankfulls before you make any conclusions about the mileage. You'll also have to fill the tank all the way up to the neck because I can put an extra gallon in the tank after the pump clicks off to be as accurate as possible. Check to see if your odometer is slipping and or if you have correct size tires. Those factors (I have oversize tires) will all affect fuel economy other than the obvious driving habits and engine condition etc.

The 84 shouldn't be getting 30-35mpg I believe it shouldn't do any better than 27-28mpg unless you have a massive tailwind and have no radio or AC on going 43mph on level ground with extra air in the tires.

Welcome to the forum.

Since you just purchased the vehicle, you may, or may not have checked and adjusted the following:

1) Air pressure in the tires.
2) Valve lash
3) Camshaft timing.
4) Injection timing.
5) Injector spray pattern.

All of these items are important for maximum economy on a diesel.

Additionally, remember that winter fuel is in use for the next several months. The best 300D turbos get 28-30 on summer fuel and this typically drops to 25-27 on winter fuel. Many folks don't achieve these numbers due to improper engine and/or vehicle settings (see 1-5 above), or driving habits (heavy city driving or 70+ on the highway).

I would urge you to obtain sufficient knowledge to verify all of the aforementioned items are correct. Then, you can complain about poor mileage and we can sympathize. Some of them simply don't get the expected mileage..........no matter what you do to them...........but, it's a rare situation.

Ok, let's say 28mpg. That is still 8 numbers difference on what I am getting. And believe me, it is accurate. I know my daily route adn I am pretty sure, I am getting those bad numbers. I know my gauge was acting up so I replaced it. The car ran out of fuel without giving me any warning light. So far I don't smell diesel outside but I do feel and hear my engine make a gargling sound driving on a slight incline at 65 to 70 mph while stepping on the gas. Smooths out when I back off a bit on the pedal.

I would definitely read Brian's post and review it.

When was the valve adjustment done last? Excessive timing chain stretch will affect timing along with the IP timing. If the injectors are cloggled or unbalanced you will get reduced power and therefore, economy. You also have to remember that the turbo 617 is more efficient than the 617 NA motor.

Have you diesel purged the motor? Are you using #1 diesel? #1 has less energy than #2. I can't compare #1 since nobody requires it in CA. :D My car has less than new compression :D but the injectors are new and it runs like a top but even being a 240D it only gets 21-23mpg around town and some freeway at no more than 65mph.

My car also starts making a tappa-tappa-tappa sound from the passenger footwell when the cetane is low (33% SVO and 67% ULSD or #2) if you back off it goes away. Dump in some cetane booster or B100 and sure enough it goes away.

The Turbo OM617 gets better milage than the non-turbo by a pretty big factor.

Dave, I've heard the same, but have no data for them. Have any data for the "typical" fuel economy on the n/a engine?

If the "best" 617 turbo engines can get 28-30 on the highway, what's the reduction for the n/a engine? I would take a WAG and say 2 mpg reduction, but, it could be more.



Anybody get better than 26-28 mpg on the highway with a n/a 617?? Not a guess.........some good data.........thanks.

I only get about 400 miles on a full tank, its an 85 300tdt, is that normal? I always fill it right up. I have never had the fuel light come on because the car is new to me and I don't want to run out of fuel.

Peter

Make sure your filters are clean too.

The EPA published these figures for the NA 617 diesel in the 1980 300D.

EPA numbers were 23 city/28 highway.

At least as was mentioned in an earlier thread.

EPA figures are inflated.
 

My son's naturally aspirated 300D only got 24 at best, usually more around 21-22. That was in a car that had 30K on a professionally rebuilt engine when we bought it.

The car was t-boned, the engine lives on in a friend's car and he also gets about 22mpg in highway use. It's now got about 100K on it, just broken in, runs like a Swiss watch. It won't get any better.

Turbo= more effeciency. My '84 turbo gets as high as 24-25, more like 21-22 when I drive it with a heavy foot. Still not 28-29 like you (or I) want, but it has 307,xxx on the odo and still runs strong.

I know some get better mileage, but part of the charm of these cars is the stone-axe reliability of the OM617, not just good fuel economy.

And let's talk driveability.

Don't forget, when these cars were first introduced in the mid '70s, smog-laden Detroit sedans typically got 12 city, 17 highway and driveability was horrible, especially when cold.

The CHP got suckered into buying some full size Dodge St. Regis sedans for their cruisers in 1979, and if they started at the bottom of Cuesta Pass outside of San Luis Obispo, they would not break 60 when they got to the top of the hill. That's how bad it was then.

Just check out some Consumer Reports from that era in the library, and see how far ahead the 617 was in terms of being able to run smoothly without stalling when cold.

Go ahead and follow thru with previous posts about things to check, they are all valid and may buy a couple of MPG-- but that will be about all.

Oddly enough,the SD will typically get better MPG even though it's heavier. My brother-in-law consistently clocked 27-29 on his 1979, and once I get my '82 on the road, I'll post results.

That's exactly what I get.

Danny

Remember also, diesel fuel of the late 70s and early 80s had better than 45 cetane. Today, you'll be lucky to get something that measures 40 cetane.

Check tire pressure too; these vehicles are responsive to properly inflated tires.

if the diesel purge helped, I consider running some good doses of dieselkleen.

Also, you odometer might be slipping a bit, mine works when its warm but not when its cold. this is a common problem.

do you have oversize tires on it?