Mileage. Miles per gallon. Fuel efficiency.

[Nevadan]

http://img594.imageshack.us/img594/7269/tdarticle.png

Per this excellent article originally posted by v8volvo these engines are rated to get 29/37 mpg.

I've put over 3,000 miles on my revitalized '85 745 (manual tranny with O/D) mostly on long trips (200 and 500 mile trips) traveling 75 - 80 mph with the A/C running and get between 26 and 29 mpg (U.S. Gallons). The engine has a rebuilt head, Monark style Bosch 273 nozzles, a remote air to oil cooler in addition to the stock water to oil cooler. I have not done a compression check but the engine starts easy and runs VERY good; there was still cross-hatching on the cylinder walls when I removed the head. I did block off the EGR flow at the exhaust manifold. Everything else is stock. I need to continue tweaking the the LDA and fuel screw adjustments since I can't seem to match the fuel delivery to the turbo boost, but it is close and does run good.

So my question is what "miles per gallon" are you getting from your vehicle running the D24T?

Am I expecting to much to get in the 30 - 35 mpg range?

I get 38 - 44 with my 1.6TD in the Jetta traveling the same speed and that engine is pretty worn out. I understand the 745 weighs about 1,000 pounds more so maybe that's the answer, I'm just looking for comparable mileage figures from similar usage.

[petercz]

I think 37mpg is a little dream cons with D24Txx. I have 27mpg mixed city/highway, but it's auto. Friend with 940 d24tic manual get average 32mpg, best 35mpg on long trip 60-70 mph, without A/C

[745 TurboGreasel]

Igot 27.5 US at 80 MPH last trip. at 55, I think 37 would be possible, but I can't see doing 55 for that long.

[anders]

I get a consistent 29mpg commuting with my 745 with auto. The best I have got with that car is 32mpg.
My 244 d24tic/m46 that's modded will do 34mpg on the same commute and the best I got was 36mpg on the trip to the Swedish car show, 36 is impressive since I was running 70-75mph and the the OD did not want to work the whole trip.

[Nevadan]

Thanks for the feedback.

I just wanted to make sure there wasn't something I was missing, like dragging an anchor or towing a parachute, that was burning up fuel, but it sounds like I'm in the ballpark.

I know my 1.6TD Jetta gets 2-5 mpg better in the winter than the summer (not running a/c, cooler oil, etc.) so I'll see what happens this fall and winter when the temperature is cooler.

If anyone wants to make a 200-400 mile 55 mph trip to see what they get I'd be interested, but I, like 745 TurboGreasel, can't drive that slow.

[Nevadan]

Here's some data from the SAE paper number 790206 titled "New 5 and 6 Cylinder VW Diesel Engines for Passenger Cars and Light Duty Trucks" dated March 1979. It's for the non-turbo engines but at least provides a guideline for the turbo engines.



The most interesting thing to me is the relationship between vehicle weight and maximum MPG.

[v8volvo]

Another interesting thing is the acceleration figures -- like the 60.2 seconds that the LT28 is quoted for 0-100km/h! Makes a 240 Diesel or a Rabbit look like a rocket by comparison....

Every one that I have had has always averaged in the high 20's. I have also noticed 240's seem to do a little better than 700s for some reason -- hard to figure out since the 700 has a better aerodynamic profile and weighs about the same, and uses the identical tranny, driveline, rear axle, etc. Automatics and manuals seem about equal for the 700 series. My automatic 745TD averages about 26-27 in mostly urban driving. I sometimes see 30+ on the road but it drops off again if you're cruising faster than 70 or 75. On a trip through Montana last spring in a 745TD with M46 I did a couple hours with the cruise locked on 85, think I saw 26 or 27 mpg then. The engine didn't mind it but aero drag at those speeds starts to play an increasingly significant role -- its force increases in proportion to the square of velocity so every additional mph starts to have a large effect.

The Volvo is lot heavier than a Rabbit or Jetta and the RWD adds a bunch of extra joints, bearings, and inertia that the FWD VW doesn't have, plus bevel gears in the rear end which are a big efficiency sucker. Probably the drivetrain difference is almost equally as significant to the MPG number as the weight is.

Worth noting, though, that a similar size and weight Mercedes from the same era only gets about 22-23 most of the time -- it's hard to see a Volvo matching those EPA numbers from that article but measured against their alternatives they're OK. I guess a Peugeot probably does a little better with about the same space inside, but owning one of those would probably make finding parts to keep a D24T going seem like a piece of cake....

[Nevadan]

All true, and thanks again for your experienced input.

I did have a 1983 Mercedes 300 N/A that got between 20 and 25 mpg, but if I drove it 75 mph with the A/C on it really worked that engine hard and only got about 20 mpg.

After driving my "new" Volvo 745 it's initial 3,000 miles I am VERY impressed with both the power and the mileage. This is, and will be, my long distance luxury car (Although I'm sure I'll be hauling an engine, tranny or other parts in it!). It's big enough to sleep in and I love the big feel of it at speed on the highway.

[ngoma]

34 MPG from my '85 M46 745, 27 MPG from the '85 4HP22L 740. After correcting for 2-3% overoptimistic speedometer. City/Hiway mixed, mileage always better during warmer weather, A/C nonop in both cars.

One of the reasons for the better mileage from the M46 is the ability to shift into overdrive at lower speeds during low-load situations, sometimes as low as 35MPH. Sort of a hypermiling tactic.