My 87 300SDL is getting 21 mpg at 90mph. that includes going up and down 6000' mountain passes on long trips. It gets about 24mph driving around town at the speed limit. Town is at 5000' altitude.

Hatterasguy has suggested that something must not be right, it should do quite a bit better than that.

I was satisfied with the mileage I was getting, until now.

I recently replaced the overflow hoses between the injectors, they were weeping a little fuel. I don't see fuel leaking anywhere else.

Any ideas?

My 86 300 sdl gets 25mpg consistently with driving half in town half on the interstate. At steady 70mph I get about 25mpg. At 60mph I get about 27 mpg.
My car has 86,000 miles on it.

John

fyi, last road trip in my 300sdl resulted in 30+ mpg at a steady 65 or so mph. oh, the bugger is showing just short of 190k on the odometer.

You drive 90 mph on long stretches? There must not be any cops around your part of the woods. The most I did was a short stunt of 90+ mph on route 5 near Bakersfield - there are too many cops around, and have seen cars stopped for speeding all the time .
I do not have an 87 300SDL, but my 87 300D gives me a consistent 28 mpg on combined city/highway, and around 30-32 mpg on highway with cruise set at 78 mph.

It might depend on your driving habbits. I know we have different engines but my mpg drops from about 26 to closer to 22 when I really romp on it. Most of the time when I'm driving on veg I lead-foot it but when I don't have any filtered or have to run on dino for whatever reason I tend to take it really easy and consequently get better mileage.

__________________
Seth

1984 300D 225K
1985 300D Donor body
1985 300D Turbo 165K. Totaled. Donor Engine. It runs!!!
1980 300SD 311K My New Baby.
1979 BMW 633csi 62K+++? Dead odo

Last week, I drove from Calgary Alberta to Twin Falls Idaho, about 850 miles in 12 hours. Cruise control was set on 90mph. I only slowed down for curves in the road where 90 was too fast and twice for the radar detector. Went down I-15, passed through Montana in less than 5 hours.

From Twin to Carson City, I slowed down a bit, to 85. I didn't want a ticket in Nevada. Other states don't share data with Nevada, so getting a ticket elsewhere doesn't affect points off my NV license.

I thought 21mpg at 90mph for 12 hours was doing pretty good for an oil-burner.

That's darned good for any car.

Leave 6 hours early for your next trip and try it at 60mph. If you get 25mpg or better then you're doing as well as can be expected.

Hatterasguy was suggesting that something is not right with you, not your SDL

Sixto

Hmm...
850mi/21mpg = 40.47gal
850mi/25mpg = 34.0gal

the difference is 6.47 gallons of deisel.

6.47gal x $3.05gal = $19.73

I can't drive for 18 hours in a row and a motel costs more than $19.73 for a night, thus it costs less to drive 90mph (so long as there is no speeding ticket).

Besides 90 is only 15 over. The posted speed in Montana is 75.

I meant that there isn't much information on the expected mpg at 90mph. Drive it at speeds for which folks around here have experience then we can advise you on whether your car is in a good state of tune. Any car that can hold 90mph for 12 hours is in a good state of tune IMO. Have you entered it in the Silver State Classic?

Sixto

First time I've heard of the Silver State Classic. Looks like fun, but my car tops out around only 116mph. Racing isn't my thing.

I drive fast because I like it, the SDL is an autobahn car and can handle it, and 90mph shaves 3hrs off of a 9hr / 540mi trip at 60mph.

It makes sense to go fast on long trips.

In the USA there are a lot of unconstitutional laws that restrict freedom to mitigate risk. Creating risk is not criminal, check your Constitution to verify. Its only criminal to cause actual damage to life or property.

90mph is a nice slow cruise for a W126.

Well I didn't know you were running 90 at 5k feet. I average high 27-28 but I keep my speeds from 70-80, also I am at sea level. The cops tend to frown at 90.

How many miles though? When was the IP timing and crank/cam timing last checked? When were the injectors last checked?

21 is probably about right at those speeds. Just for kicks slow the next tank down to 75 or 80 and see if it makes a difference.

__________________
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1969 280SE
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2007 Tiara 3200

I'm curious to see EGTs during a long hard 90mph uphill pull at altitude. I remember a hard run up the grapevine section of I-5 had my temp gauge pegged at 110 (it went from 90 to 110 pretty quickly then stayed at 110). I can only imagine what the turbo sees. In a gasser turbo this type of driving leaves the turbine housing aglow

Sixto

So the ambient air pressure makes a difference? I have had the car only a year and haven't checked the IP, the timing or the injectors.

Its got 207k miles on it. It seems to run really well; what is the line between good enough and anal attention to detail? It gets 24 - 25 mpg when running between 40 and 70, thats average small town driving with some freeway time to the big city, Reno.

So it probably could be tweaked for some improvement, but at what cost? $500? $1000? Depends on if I do the work, and/or if it needs new injector/s.

Sometimes, better is the enemy of good enough.

The EGT would be interesting, I don't have one. I was watching the coolant temp very closely. It would usually run between 80 - 90C, but when climbing hills, it would go just a little past 100C. The outside air temp wasn't bad, 50-70F. I didn't run the A/C and had the sunroof open a bit, mostly to chuck out the pistachio shells.

Also I'd hold the camera-phone up out the roof to take photos, once in a while. The first time I did it, I darn near lost the phone to the 80mph wind. They are here: http://www.nemitz.net/photos

That's my question too - how sensitive is the ALDA to altitude? Presumably the ALDA has its roots as an altitude compensation device. Does increasing it's operating range to cover 0-30 psia mean it's less sensitive to changes in the tenths of a psi range?

Hatterasguy has you all paranoid. Folks who squeeze better mileage than that out of an SDL can squeeze as much out of a 560SEL. Now I retreat to my corner and wait for Brian to rebut

Sixto