W123 280E Fuel Usage and Trans shifts.

[cheapold280ce]

That's 25 cents a mile how far is your commute?

[79Mercy]

Not far, maybe 10 miles max.

[todds]

That's almost as cheap as the subway! Gas mileage isn't everything. That said, a car that gets less than 15mpg can be pretty painful on any kind of long (in other words fun) trip!

I'm not getting much better in an old carb'ed 2.3L six which revs to the sky. It's pretty solidly around 16-17 and city or hwy makes little difference. Neither does it matter much if I am gentle or not. I get into the secondaries all the time with the tiny primaries on the Webers. I could probably approach 20 with a better diff and some fiddling and also lower the stress factor on the hwy.

I've heard nothing but positive comments for going to a more suitable diff on an old Mercedes, if you can get your hands on one. You said your guages are broken anyway right? So at least you won't have to worry about them being off ;-)

[280EZRider]

Sorry, I forgot to mention one minor detail when quoting my 20mpg on the highway - 80 mph

[tc20]

I recently bought a 280E auto (euro obviously) and have done a couple of check on the consumption -

mostly highway driving (averaging 85mph) 24mpg

town driving/short commutes (5miles each way daily) 21.5mpg

The gallons im talking about are Imperial measure (1 Imperial gallon = 1.2 US gallons)

Also, petrol (gas) is €1.31 per litre here, which works out at US$ 9.22 for an Imperial gallon

I have to say tho, the car is a beaut to drive, with bags of power, and feels like it was hewn from granite

[t walgamuth]

Originally Posted by 280EZRider

Sorry, I forgot to mention one minor detail when quoting my 20mpg on the highway - 80 mph

This I would say is impossible unless you have undersize tires and haven't corrected for them.

And the fellow claiming over 20 with a 380 I say the same thing, inaccuracy in calculation is the only possible explanation unless he has found a 1.5 gear ratio to swap in.

Sorry.

Tom W

[Mark DiSilvestro]

Originally Posted by tc20

I recently bought a 280E auto (euro obviously) and have done a couple of check on the consumption -

mostly highway driving (averaging 85mph) 24mpg

town driving/short commutes (5miles each way daily) 21.5mpg

The gallons im talking about are Imperial measure (1 Imperial gallon = 1.2 US gallons)

Also, petrol (gas) is €1.31 per litre here, which works out at US$ 9.22 for an Imperial gallon

I have to say tho, the car is a beaut to drive, with bags of power, and feels like it was hewn from granite

That works out to 20 and 17.9 miles per US gallon respectively.
Also, keep in mind that US versions had 5 mph bumpers and were almost always fully equipped with power-windows, electric sunroof, cruise-control, automatic tranny and automatic climate control, causing them to be somwhat heavier than their European counterparts. This, coupled with lower compression (8:1 US vs 9:1 Euro) tends to reduce fuel economy as well as performance for a US-market 280E.

Incidentally, My '84 Euro 300TD (Non-turbo, 5-speed, 3.46 rear end ratio) averaged out to over 30 mpg on my last tank in mixed city-highway driving.
Unfortunately, I have to deduct about 15% off my speedometer/odometer readings because I believe whoever originally imported this car replaced the kmph speedometer with mph one for a US turbo 300D/TD (3.07 ratio) and the speed / mile readings are now too high. So my calculated actual mpg is 26.

Happy Motoring, Mark

[t walgamuth]

With my 280e euro and five speed with a 369 rear I had trouble exceeding 23 hiway.

I don't see how you could get 26 for a mixed tank unless there was a lot of 45 mph running without any stop signs.

Have you checked the speedo and odo against the mile markers and the stopwatch?

Tom W

[Mark DiSilvestro]

Originally Posted by t walgamuth

With my 280e euro and five speed with a 369 rear I had trouble exceeding 23 hiway.

I don't see how you could get 26 for a mixed tank unless there was a lot of 45 mph running without any stop signs.

Have you checked the speedo and odo against the mile markers and the stopwatch?

Tom W

Because my '84 Euro is a 5-cylinder diesel with a 5-speed, and 3.46 rear-end ratio.
Now I haven't yet taken a long enough highway trip with the TD to check it against the mile markers, but the seller admitted the speedometer read high on this car, and I compared the odometer reading on the TD (36 miles) against the one on my '98 Nissan Altima (31 miles) during the trips I made to College-Park, Maryland to see the TD, and bring it back to Mount Vernon, Virginia.
(I have checked the speedometer on my Nissan with highway markers, as well as roadside speed-enforcement radar warning signs)

Happy Motoring, Mark

[t walgamuth]

Originally Posted by Mark DiSilvestro

Because my '84 Euro is a 5-cylinder diesel with a 5-speed, and 3.46 rear-end ratio.
Now I haven't yet taken a long enough highway trip with the TD to check it against the mile markers, but the seller admitted the speedometer read high on this car, and I compared the odometer reading on the TD (36 miles) against the one on my '98 Nissan Altima (31 miles) during the trips I made to College-Park, Maryland to see the TD, and bring it back to Mount Vernon, Virginia.
(I have checked the speedometer on my Nissan with highway markers, as well as roadside speed-enforcement radar warning signs)

Happy Motoring, Mark

Sorry, I guess I thought you were speaking of a 280e. The 300d is a different animal. I can get 30 mpg highway with mine with the 307 and a four speed. I would think you can do that with yours setup too.

tom W

[cheapold280ce]

A manual for 1978 passenger cars USA versions has the fuel comsumption listed fot the 280CE and 300CD as follows:

For 280CE Federal version 16 mpg at 68 mph
280CE CALI version 15 mpg at 68 mph
300CD 20 mpg at 68 mph

For average cross country driving:

280CE 12-20 mpg
300CD 17-26 mpg

[sjefke]

Guys, be careful with the thermal expansion of fuel. mpg readings based on refills may have an error if you fill up during a cold morning and refill on a hot afternoon. You think you used less fuel than you actually did because the remaining fuel in the tank has expanded.

Bert

[Mark DiSilvestro]

Originally Posted by sjefke

Guys, be careful with the thermal expansion of fuel. mpg readings based on refills may have an error if you fill up during a cold morning and refill on a hot afternoon. You think you used less fuel than you actually did because the remaining fuel in the tank has expanded.

Bert

Was wondering if thermal expansion affects diesel as much as gasoline. In any case, my last refill with the TD was on a chilly afternoon. No such luck now as we're in for our first heatwave of the season, following yesterday's brutal thunderstorms that left me without electric for 26 hours. I'm hoping my TD will top 30 mpg on it's first highway trip. (And also hoping to find a correct replacement speedometer, so I won't need to perform extra calculations every time I want to tally my fuel mileage)

Happy Motoring, Mark

[sjefke]

I tried to find diesel thermal expansion coefficient before my post but could not find it. I was talking to a trucking company the other day that is working on getting better mpg (they are at 7 mpg...) and they mentioned that it can be significant. But then again, much bigger tanks and volumes.

To overcome speedo errors, try borrowing a GPS unit from somebody. We have a Garmin Nuvi and it gives very accurate speed and mileage readings. Can help calibrate your speedo.

Good luck,

Bert

[Mark DiSilvestro]

Originally Posted by sjefke

I tried to find diesel thermal expansion coefficient before my post but could not find it. I was talking to a trucking company the other day that is working on getting better mpg (they are at 7 mpg...) and they mentioned that it can be significant. But then again, much bigger tanks and volumes.

To overcome speedo errors, try borrowing a GPS unit from somebody. We have a Garmin Nuvi and it gives very accurate speed and mileage readings. Can help calibrate your speedo.

Good luck,

Bert

Well, I already know the error factor, which is 15%.
What I believe I need now is a speedometer from a non-turbo 300D/TD with a 3.46 rear end ratio. Or some way of determining (by part number perhaps) if one of my spare W123 speedometers is compatible with my Euro TD.

Happy Motoring, Mark