I couldn't believe my eyes when I filled up after a day trip. The only change from last years best run of 30.5 mpg was the change in oil. Usually I run Mobil One 10W30 but this time I had switched to Castrol Syntec 5W30.
FYI mods, M46, 3.31 rear gears, lowered, synthetic fluids all around, tires inflated to 38-40 psi. I also run a maintenance dose of Auto-Rx in the oil and run Lube Control FP60 in the gas. Also the air filter is an OEM paper unit.
1987 745T with 349,300 miles, engine has 66,700 miles on it.

I have run Mobil One with 5K mile oil change intervals since the day I fired it up. The change to Castrol Syntec was in the last 3K miles.

This trip was limited to a maximum 65 mph and in the 55 mph zones I was running 60-62 mph. I didn't use the AC at all during the trip. The weather was perfect in the 60's and no wind.

I one thing I did notice was how smooth the car accelerated coming out of the rest area up to speed with out using the turbo.

Your fuel economy improvement is most likely due to something other than the oil change. The difference in engine efficiency due to a change from Brand A 10W30 to Brand B 5W30 would be infinitesimal at operating temperature (ie: on the highway).

That's great fuel economy and obviously the car is in top condition...but there are so many variables in the MPG's of a given tankful, that a change of engine oil types would be buried behind more significant factors.
--
Bob (son's 81-244GL B21F/M46, dtr's 83-244DL B23F/M46, my 94-944 B230FD and 89 745 (LT-1 V8); hobbycar 77 MGB, and a few old motorcycles)

I noticed the same sort of thing. I did some tune up work (plugs, etc.) then two weeks later changed my oil from Pennzoil(I'm cheap and it's DUSTY here) 15-40 to 10-30 and saw a 2 mpg improvement from ~20 to ~22.

Since, it's dropped off again. More maintenance to be done. I can't imagine my misaligned P/S pulley (due to worn bracket. The new one is in my trunk) is doing my mileage any favors. Or the worn tie rod, which might be related to the wheel shimmy I have.

-Will
--
1990 740 Turbo, on its way to stock specs, maybe beyond

synthetic doesn't deteriorate like petro so there is no need to change it.I've gone a yr.on amsoil&its still ok,just change the filter

...but then again, I have a diesel!

I had an '86 745GL with ZF Auto tranny w/lock-up that got some of the best mileage of any Volvo I've ever owned (had 122s, 140's, 240' 740's 960's and V70's).

I got 32.5 mpg highway regularly, only to be outdone by my '04 V702.5T which did 33.1 mpg best
--
'89 245 sportwagon, destroyed by hit & run driver, RIP. '04 V70 2.5 T Sportwagon, 12k mi and '91 245 5-speed, 209k mi, replaced the '89

Ditto on my 87 744GLE w/ZF. Low 30's easy...
Precipitous drop with the 93 945 (no turbo) with whatever they put in for the trans..., 27 MPG at best.
27ish also with the V90 I have now, but the ride alone is worth it..And the power.. While the hills on the Taconic used to be a grind in the 93, the V makes them disappear..

Dr. Chip
Westchester County NY.
98 V90

Taconic! Great driving road. In '94 after I bought the '86 745 GLE (my mistake, it was not a GL, as only the GLE got the ZF w/lock-up) I drove from Texas to New England and on the way back, went from Albany down the Taconic Parkway, then the Saw Mill, acroos the Tappan Zee to US 209 along the Deleware Water Gap, then down the Skyline Drive, Blue Ridge Parkway through Atlanta, New Orleans and home. Combined mpg for the whole trip was a tad below 30 mpg. Considering the back roads, switchbacks, and round-about way we drove, that wasn't too bad. Nice ride, though
--
'89 245 sportwagon, destroyed by hit & run driver, RIP. '04 V70 2.5 T Sportwagon, 12k mi and '91 245 5-speed, 209k mi, replaced the '89

Sounds like a great trip. The Taconic to Delaware bit is some of the most beautiful driving in the North East. It is sometimes hard to reconcile that at no point are you more than 2 hours or so from NYC..You can even see the Big Apple from the Tappan Zee..

(BTW, my uncle built the Taconic for NYS in the 30's...)

As for the Volvos. I personally loved the ZF/744GLE combo. Even w/o a turbo, the car was relatively peppy, shifted nicely and returned amazing MPG's..

Never liked whatever was in the 93 945...

Best

Dr. Chip
Westchester County, NY.

I have a '93 940 (turbo) and the tranny might be shot, so... should I be looking to replace it with an earlier model to get better mileage?

How did you end up with the 3.31:1 rear end ratio?

The best I have ever got is just over 28 mpg with my 1987 745T. I've got that twice. My wife's 1986 745T often gets 27 mpg on the freeway.
--
john

Swap the rear end out when I changed out the AW71 to a M46. The original rear gears were 4.10's.

I thought your car was originally a factory turbo. Should have had 3.73:1 ratio rear end. The 4.10:1 ratio was used in B230F equipped 745s with AW70.

Is there something I am unaware of?
--
john

No with my car it came with either 3.90 or 4.10. I know the manual says 3.73 is what supposedly came in it. When I checked it the drive shaft rotated 4 times for one turn of the wheel. Not 3.75 but 4 rotations. Normally with the AW-71 I saw 3K rpms at 78 mph. 70 mph with the 3.31's and the M46 is 2450.
3K rpms will get me up to around 84 mph.

I've got the same setup and on a run to Ohio from Maryland and back last weekend I was getting high twenties and up. The last tankful from PA (without Ethanol) got me 420 miles on just over 15 gallons and I don't drive slow.
--
The Breadbox - 1989 740 GL Wagon in White