84 300SD Mileage Woes - PeachParts Mercedes-Benz Forum

meltedpanda · #1 12-15-2004, 12:34 PM

Just seems like I should be getting better than 22MPG. Straight highway goes up to 24-25. Normal or not?
I am not a heavy foot driver although I do an italian tune up at least 1 time per week.
What do you all get for mileage?

Scott98 · #2 12-15-2004, 01:10 PM

There have been several threads in the past where people posted their mileage. It really varies. I get about 26 on the hwy in my '85 300D. Some people get 30, others 24. It all depends.

Scott

Brian Carlton · #3 12-15-2004, 01:26 PM

If you are suffering from the winter fuel, it's not too far off the mark. The SD would drop down to about 24-25 in the winter. This is about 90% highway miles. So, 22 with a good percentage city, is probably normal.

You can try for some gains by ensuring that the EGR is disconnected and plugged and that all the tires are running 32 psi.

I've also found that the Power Service conditioner pays for itself in improved economy on the SDL. Have not tested it on the SD, however.

vwbuge · #4 12-15-2004, 05:19 PM

You failed to mention how many miles on your SD. My car has about 300,000 miles and runs wonderfully. However, I only manage 22 MPG.

tenknots · #5 12-16-2004, 07:37 AM

My last fillup was yesterday (I do it every 4 days or so) and I got 29.7. Mostly hiway, 60ish with some traffic crawling thrown in. Winter fuel has had no effect. I think you should be getting better. Does your car smoke alot?

meltedpanda · #6 12-16-2004, 10:56 AM

my 84 300SD has 152K on it. I have the valves done per schedule and perform all maintenace intervals religiously. She does not smoke at all
great pick up and performance, just low (I think) mileage.

braverichard · #7 12-16-2004, 12:04 PM

I'm in the same position as you, though I have pretty much given up and I'll just stick with what I am getting. I have 156K on my '84 300SD and the only diesel sold here (summer or winter) is #2. My valves and timing are all properly set. Fuel filters all new and diesel purge was just done 2,000 miles ago or so after which I changed the fuel filters. Air filter is just 4,000 miles old. After driving 80% highway (65 - 70mph) and 20% in the city, the best I get somtimes is 24 mpg. In fact, usually I get around 22mpg. I've even used gumout diesel injector cleaner between fill-ups. At this point, I've done all there is to do so I've given up. I'll just keep my average 22mpg. Not bad for a 20-year old 4,000 lb, full size, rear wheel drive sedan. Just that I have a funny feeling that a 3.0L gas V6 engine with more power and torque would be getting better mileage if placed in this car. Oh well!!

meltedpanda · #8 12-16-2004, 01:21 PM

Quote:

Originally Posted by braverichard

. Just that I have a funny feeling that a 3.0L gas V6 engine with more power and torque would be getting better mileage if placed in this car. Oh well!!

but it won't sound as good or last as long, you can be assured!

Sounds like my mileage is average, thats OK, I am an average kinda guy

pawoSD · #9 12-16-2004, 01:58 PM

The way I drive I have been averaging 20.3 mpg on the last few tanks

Once however, I did drive very conservatively for an entire tank just to see how much better I could get, and I averaged around 25.8, mostly city too....so I guess that goes to show how lead footed I am

Our 3.0liter V6 van only gets 14-15 in the city with the way me and my dad drive it.....

its rated 19 city/23 hwy

braverichard · #10 12-16-2004, 03:12 PM

Quote:

Originally Posted by meltedpanda

but it won't sound as good or last as long, you can be assured!

Sounds like my mileage is average, thats OK, I am an average kinda guy

What kind of mileage do you average on that money pit of yours? Also state the proportion of city and highway driving and driving style. I know for sure the 603 is a much more efficient engine than the 617.

Hatterasguy · #11 12-16-2004, 03:27 PM

The 603's are not much better, I get a rock solid 23.5 every tank regardless of how I drive. One tank where I did a lot of highway I did manage 24.

Even on winter fuel I am not 100% sure yet but I think my mileage is only down to 23 or so.

braverichard · #12 12-16-2004, 04:30 PM

What's the deal with winter diesel being mentioned all over the board? Over here in Kansas City we have the same diesel all year round as far as I know: #2. The only exception being the truck stop just about 30 miles south of KC where you can get #1 between May and October.

Wodnek · #13 12-16-2004, 05:08 PM

Generally the pump still says #2 but it is blended with some additives including #1 to keep it from clouding or jelling up. I think that is for anywhere that gets below freezing but am not positive.

dannym · #14 12-17-2004, 09:30 AM

Hey,
I don't buy into the "just live with it" when your not getting the right mileage.
If your not losing compression then something just isn't right.
Maybe a clogged fuel filter or injector.
Clogged intake manifold. I've seen some pretty nasty pictures of that right here on this site. Clogged air filter.
Not tuned properly.

I'm no expert, those are just some things I thought of off the top of my head. The point I'm trying to make is if your not getting the right mileage then there is more than likely something you can do to correct it.

Danny

braverichard · #15 12-17-2004, 10:50 AM

I've checked everything there is to check, including even my valve clearances. There isn't anything else left. I'll have my mechanic check my brakes to make sure no calipers are dragging later today.

Anyway, I believe 23mpg is about as good as that 617.951 motor can do.